Dubbo2.7源码详解

Spring与Dubbo整合原理与源码分析

　　【1】注解@EnableDubbo

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
@EnableDubboConfig   // @EnableDubboConfig注解用来将properties文件中的配置项转化为对应的Bean
@DubboComponentScan  // @DubboComponentScan注解用来扫描服务提供者和引用者(@Service与@Reference)
public @interface EnableDubbo {

    @AliasFor(annotation = DubboComponentScan.class, attribute = "basePackages")
    String[] scanBasePackages() default {};

    @AliasFor(annotation = DubboComponentScan.class, attribute = "basePackageClasses")
    Class[] scanBasePackageClasses() default {};

    @AliasFor(annotation = EnableDubboConfig.class, attribute = "multiple")
    boolean multipleConfig() default true;

}

 

　　【2】注解@EnableDubboConfig

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
@Import(DubboConfigConfigurationRegistrar.class)
public @interface EnableDubboConfig {

    boolean multiple() default true;
}

　　　　1）DubboConfigConfigurationRegistrar类的作用

//因为实现了ImportBeanDefinitionRegistrar接口，spring容器就会实例化该类，并且调用其registerBeanDefinitions方法；
public class DubboConfigConfigurationRegistrar implements ImportBeanDefinitionRegistrar {
    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
        //执行DubboConfigConfigurationRegistrar;

        AnnotationAttributes attributes = AnnotationAttributes.fromMap(
                importingClassMetadata.getAnnotationAttributes(EnableDubboConfig.class.getName()));

        boolean multiple = attributes.getBoolean("multiple"); //默认值是true

        // Single Config Bindings
        registerBeans(registry, DubboConfigConfiguration.Single.class);

        if (multiple) { // Since 2.6.6 https://github.com/apache/dubbo/issues/3193
            registerBeans(registry, DubboConfigConfiguration.Multiple.class);
        }
    }
}

 

　　　　2）registerBeans做了什么

public static void registerBeans(BeanDefinitionRegistry registry, Class... annotatedClasses) {
    if (ObjectUtils.isEmpty(annotatedClasses)) {
        return;
    }
    ...
    AnnotatedBeanDefinitionReader reader = new AnnotatedBeanDefinitionReader(registry);
    ...
    // 利用Spring中的AnnotatedBeanDefinitionReader来解析annotatedClasses
    // 会解析该类上的注解，然后进行处理
    reader.register(annotatedClasses);

}

 

　　　　3）DubboConfigConfiguration类展示

public class DubboConfigConfiguration {

    /**
     * Single Dubbo {@link AbstractConfig Config} Bean Binding
     */
    @EnableDubboConfigBindings({
            @EnableDubboConfigBinding(prefix = "dubbo.application", type = ApplicationConfig.class),
            @EnableDubboConfigBinding(prefix = "dubbo.module", type = ModuleConfig.class),
            @EnableDubboConfigBinding(prefix = "dubbo.registry", type = RegistryConfig.class),
            @EnableDubboConfigBinding(prefix = "dubbo.protocol", type = ProtocolConfig.class),
            @EnableDubboConfigBinding(prefix = "dubbo.monitor", type = MonitorConfig.class),
            @EnableDubboConfigBinding(prefix = "dubbo.provider", type = ProviderConfig.class),
            @EnableDubboConfigBinding(prefix = "dubbo.consumer", type = ConsumerConfig.class),
            @EnableDubboConfigBinding(prefix = "dubbo.config-center", type = ConfigCenterBean.class),
            @EnableDubboConfigBinding(prefix = "dubbo.metadata-report", type = MetadataReportConfig.class),
            @EnableDubboConfigBinding(prefix = "dubbo.metrics", type = MetricsConfig.class)
    })
    public static class Single {}

    /**
     * Multiple Dubbo {@link AbstractConfig Config} Bean Binding
     */
    @EnableDubboConfigBindings({
            @EnableDubboConfigBinding(prefix = "dubbo.applications", type = ApplicationConfig.class, multiple = true),
            @EnableDubboConfigBinding(prefix = "dubbo.modules", type = ModuleConfig.class, multiple = true),
            @EnableDubboConfigBinding(prefix = "dubbo.registries", type = RegistryConfig.class, multiple = true),
            @EnableDubboConfigBinding(prefix = "dubbo.protocols", type = ProtocolConfig.class, multiple = true),
            @EnableDubboConfigBinding(prefix = "dubbo.monitors", type = MonitorConfig.class, multiple = true),
            @EnableDubboConfigBinding(prefix = "dubbo.providers", type = ProviderConfig.class, multiple = true),
            @EnableDubboConfigBinding(prefix = "dubbo.consumers", type = ConsumerConfig.class, multiple = true),
            @EnableDubboConfigBinding(prefix = "dubbo.config-centers", type = ConfigCenterBean.class, multiple = true),
            @EnableDubboConfigBinding(prefix = "dubbo.metadata-reports", type = MetadataReportConfig.class, multiple = true),
            @EnableDubboConfigBinding(prefix = "dubbo.metricses", type = MetricsConfig.class, multiple = true)
    })
    public static class Multiple {}
}

 

　　　　4）那么必然又会解析到@EnableDubboConfigBindings注解

//又是利用了实现了ImportBeanDefinitionRegistrar接口，在实例化该类会调用其registerBeanDefinitions方法；
public class DubboConfigBindingsRegistrar implements ImportBeanDefinitionRegistrar, EnvironmentAware {

    private ConfigurableEnvironment environment;

    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
        //执行DubboConfigBindingsRegistrar
        AnnotationAttributes attributes = AnnotationAttributes.fromMap(importingClassMetadata.getAnnotationAttributes(EnableDubboConfigBindings.class.getName()));

        // 拿到多个@EnableDubboConfigBinding注解
        AnnotationAttributes[] annotationAttributes = attributes.getAnnotationArray("value");

        DubboConfigBindingRegistrar registrar = new DubboConfigBindingRegistrar();
        //将环境变量注入
        registrar.setEnvironment(environment);

        for (AnnotationAttributes element : annotationAttributes) {
            // 逐个解析@EnableDubboConfigBinding注解，比如@EnableDubboConfigBinding(prefix = "dubbo.application", type = ApplicationConfig.class)
            registrar.registerBeanDefinitions(element, registry);
        }
    }

    @Override
    public void setEnvironment(Environment environment) {
        Assert.isInstanceOf(ConfigurableEnvironment.class, environment);
        this.environment = (ConfigurableEnvironment) environment;
    }

}

 

　　　　5）registrar.registerBeanDefinitions方法的调用情况

public class DubboConfigBindingRegistrar implements ImportBeanDefinitionRegistrar, EnvironmentAware {

    private final Log log = LogFactory.getLog(getClass());

    private ConfigurableEnvironment environment;

    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {

        //执行DubboConfigBindingRegistrar

        AnnotationAttributes attributes = AnnotationAttributes.fromMap(importingClassMetadata.getAnnotationAttributes(EnableDubboConfigBinding.class.getName()));

        registerBeanDefinitions(attributes, registry);

    }

    protected void registerBeanDefinitions(AnnotationAttributes attributes, BeanDefinitionRegistry registry) {

        // prefix = "dubbo.application"
        String prefix = environment.resolvePlaceholders(attributes.getString("prefix"));

        // type = ApplicationConfig.class
        Classextends AbstractConfig> configClass = attributes.getClass("type");

        boolean multiple = attributes.getBoolean("multiple");
        //针对配置分别进行注册成Bean对象，方法1
        registerDubboConfigBeans(prefix, configClass, multiple, registry);

    }

    //方法1，因为Single和Multiple都是走同一套逻辑，采用参数boolean multiple区分
    private void registerDubboConfigBeans(String prefix, Classextends AbstractConfig> configClass, boolean multiple, BeanDefinitionRegistry registry) {

        // 从properties文件中根据前缀拿对应的配置项，比如根据dubbo.application前缀，
        // 就可以拿到如下配置：
        // dubbo.application.name=dubbo-demo-provider-application
        // dubbo.application.logger=log4j
        Map properties = getSubProperties(environment.getPropertySources(), prefix);

        // 如果没有相关的配置项，则不需要注册BeanDefinition
        if (CollectionUtils.isEmpty(properties)) {
            if (log.isDebugEnabled()) {
                log.debug(...);
            }
            return;
        }

        // 根据配置项生成beanNames，为什么会有多个？
        // 普通情况一个dubbo.application前缀对应一个ApplicationConfig类型的Bean
        // 特殊情况下（配置两种协议），比如dubbo.protocols对应了：
        //        dubbo.protocols.p1.name=dubbo
        //        dubbo.protocols.p1.port=20880
        //        dubbo.protocols.p1.host=0.0.0.0

        //        dubbo.protocols.p2.name=http
        //        dubbo.protocols.p2.port=8082
        //        dubbo.protocols.p2.host=0.0.0.0
        // 那么就需要对应两个ProtocolConfig类型的Bean，那么就需要两个beanName:p1和p2

        // 这里就是multiple为true或false的区别，名字的区别，根据multiple用来判断是否从配置项中获取beanName
        // 如果multiple为false，则看有没有配置id属性，如果没有配置则自动生成一个beanName.
        Set beanNames = multiple ? resolveMultipleBeanNames(properties) : Collections.singleton(resolveSingleBeanName(properties, configClass, registry));

        for (String beanName : beanNames) {
            // 为每个beanName,注册一个空的BeanDefinition，方法2
            registerDubboConfigBean(beanName, configClass, registry);

            // 为每个bean注册一个DubboConfigBindingBeanPostProcessor的Bean后置处理器，方法3
            //这里存在的问题就是对应每一种配置都会产生对应的BeanPostProcessor，最多好像也就是10种左右
            //但其实一个就可以做的任务，拓展成多个貌似不太合理，结合处理逻辑都是同一套就很尴尬
            registerDubboConfigBindingBeanPostProcessor(prefix, beanName, multiple, registry);
        }

        // 注册一个NamePropertyDefaultValueDubboConfigBeanCustomizer的bean
        registerDubboConfigBeanCustomizers(registry);

    }

    //方法2，为对应的配置生成一个beanDefinition，并注入到容器
    private void registerDubboConfigBean(String beanName, Classextends AbstractConfig> configClass,BeanDefinitionRegistry registry) {

        BeanDefinitionBuilder builder = rootBeanDefinition(configClass);

        AbstractBeanDefinition beanDefinition = builder.getBeanDefinition();

        registry.registerBeanDefinition(beanName, beanDefinition);   // ApplicatinoConfig对象

        if (log.isInfoEnabled()) {
            log.info("...); //日志记录
        }

    }

    //方法3
    private void registerDubboConfigBindingBeanPostProcessor(String prefix, String beanName, boolean multiple,BeanDefinitionRegistry registry) {

        // 注册一个DubboConfigBindingBeanPostProcessor的Bean
        // 每个XxConfig的Bean对应一个DubboConfigBindingBeanPostProcessor的Bean
        // 比如，一个ApplicationConfig对应一个DubboConfigBindingBeanPostProcessor，
        // 一个ProtocolConfig也会对应一个DubboConfigBindingBeanPostProcessor
        // 在构造DubboConfigBindingBeanPostProcessor的时候会指定构造方法的值，这样就可以区别开来了

        Class processorClass = DubboConfigBindingBeanPostProcessor.class;

        BeanDefinitionBuilder builder = rootBeanDefinition(processorClass);

        // 真实的前缀，比如dubbo.registries.r2
        String actualPrefix = multiple ? normalizePrefix(prefix) + beanName : prefix;

        // 添加两个构造方法参数值，所以会调用DubboConfigBindingBeanPostProcessor的两个参数的构造方法
        builder.addConstructorArgValue(actualPrefix).addConstructorArgValue(beanName);

        AbstractBeanDefinition beanDefinition = builder.getBeanDefinition();

        beanDefinition.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);

        registerWithGeneratedName(beanDefinition, registry);

        if (log.isInfoEnabled()) {
            log.info(...);
        }

    }

    private void registerDubboConfigBeanCustomizers(BeanDefinitionRegistry registry) {
        registerInfrastructureBean(registry, BEAN_NAME, NamePropertyDefaultValueDubboConfigBeanCustomizer.class);
    }

    @Override
    public void setEnvironment(Environment environment) {
        Assert.isInstanceOf(ConfigurableEnvironment.class, environment);
        this.environment = (ConfigurableEnvironment) environment;

    }

    private Set resolveMultipleBeanNames(Map properties) {
        Set beanNames = new LinkedHashSet();

        // 比如dubbo.protocols.p1.name=dubbo的propertyName为p1.name
        for (String propertyName : properties.keySet()) {

            // propertyName为p1.name
            int index = propertyName.indexOf(".");
            if (index > 0) {
                // 截取beanName名字为p1
                String beanName = propertyName.substring(0, index);
                beanNames.add(beanName);
            }
        }
        return beanNames;

    }

    private String resolveSingleBeanName(Map properties, Classextends AbstractConfig> configClass,BeanDefinitionRegistry registry) {

        // 配置了dubbo.application.id=appl，那么appl就是beanName
        String beanName = (String) properties.get("id");
        // 如果beanName为null，则会进入if分支，由spring自动生成一个beanName,比如org.apache.dubbo.config.ApplicationConfig#0
        if (!StringUtils.hasText(beanName)) {
            BeanDefinitionBuilder builder = rootBeanDefinition(configClass);
            beanName = BeanDefinitionReaderUtils.generateBeanName(builder.getRawBeanDefinition(), registry);
        }

        return beanName;

    }

}

 

　　　　6）单个DubboConfigBindingBeanPostProcessor的展示（删减掉部分不怎么用到的）

public class DubboConfigBindingBeanPostProcessor implements BeanPostProcessor, ApplicationContextAware, InitializingBean, BeanDefinitionRegistryPostProcessor {

    private final String prefix;

    private final String beanName;

    private DubboConfigBinder dubboConfigBinder;
    ....
    private List configBeanCustomizers = Collections.emptyList();
　　....
　　
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {

        // 每个XxConfig对应一个BeanPostProcessor，所以每个DubboConfigBindingBeanPostProcessor只处理对应的beanName
        if (this.beanName.equals(beanName) && bean instanceof AbstractConfig) {

            AbstractConfig dubboConfig = (AbstractConfig) bean;
            // 从properties文件中获取值，并设置到dubboConfig对象中
            bind(prefix, dubboConfig);

            // 设置dubboConfig对象的name属性，设置为beanName
            customize(beanName, dubboConfig);

        }

        return bean;

    }

    private void bind(String prefix, AbstractConfig dubboConfig) {
        dubboConfigBinder.bind(prefix, dubboConfig);

        if (log.isInfoEnabled()) {
            log.info(...);
        }
    }

    private void customize(String beanName, AbstractConfig dubboConfig) {
        for (DubboConfigBeanCustomizer customizer : configBeanCustomizers) {
            customizer.customize(beanName, dubboConfig);
        }
    }

   ...
    @Override
    public void afterPropertiesSet() throws Exception {
        initDubboConfigBinder();        // 创建DefaultDubboConfigBinder
        initConfigBeanCustomizers();
    }

    private void initDubboConfigBinder() {
        if (dubboConfigBinder == null) {
            try {
                // 先从Spring容器中获取DubboConfigBinder，默认获取不到
                dubboConfigBinder = applicationContext.getBean(DubboConfigBinder.class);
            } catch (BeansException ignored) {
                if (log.isDebugEnabled()) {
                    log.debug("DubboConfigBinder Bean can't be found in ApplicationContext.");
                }
                // Use Default implementation
                // 生成一个默认的
                dubboConfigBinder = createDubboConfigBinder(applicationContext.getEnvironment());
            }
        }

        dubboConfigBinder.setIgnoreUnknownFields(ignoreUnknownFields);
        dubboConfigBinder.setIgnoreInvalidFields(ignoreInvalidFields);

    }

    private void initConfigBeanCustomizers() {
        // 得到之前创建了的NamePropertyDefaultValueDubboConfigBeanCustomizer
        Collection configBeanCustomizers = beansOfTypeIncludingAncestors(applicationContext, DubboConfigBeanCustomizer.class).values();

        this.configBeanCustomizers = new ArrayList<>(configBeanCustomizers);
        AnnotationAwareOrderComparator.sort(this.configBeanCustomizers);
    }
...
}

 

　　【3】注解@DubboComponentScan

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(DubboComponentScanRegistrar.class)
public @interface DubboComponentScan {

    String[] value() default {};

    String[] basePackages() default {};

    Class[] basePackageClasses() default {};

}

 

　　　　1）导入的DubboComponentScanRegistrar类做了什么

/又是利用了实现了ImportBeanDefinitionRegistrar接口，在实例化该类会调用其registerBeanDefinitions方法；
public class DubboComponentScanRegistrar implements ImportBeanDefinitionRegistrar {

    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
        //执行DubboComponentScanRegistrar

        // 拿到DubboComponentScan注解所定义的包路径，扫描该package下的类，识别这些类上
        Set packagesToScan = getPackagesToScan(importingClassMetadata);

        // 注册ServiceAnnotationBeanPostProcessor一个Bean
        // 实现了BeanDefinitionRegistryPostProcessor接口，所以在Spring启动时会调用postProcessBeanDefinitionRegistry方法
        // 该方法会进行扫描，扫描@Service注解了的类，然后生成BeanDefinition（会生成两个，一个普通的bean，一个ServiceBean），后续的Spring周期中会生成Bean
        // 在ServiceBean中会监听ContextRefreshedEvent事件，一旦Spring启动完后，就会进行服务导出
        registerServiceAnnotationBeanPostProcessor(packagesToScan, registry);

        // 注册ReferenceAnnotationBeanPostProcessor
        // 实现了AnnotationInjectedBeanPostProcessor接口，继而实现了InstantiationAwareBeanPostProcessorAdapter接口
        // 所以Spring在启动时，在对属性进行注入时会调用AnnotationInjectedBeanPostProcessor接口中的postProcessPropertyValues方法
        // 在这个过程中会按照@Refrence注解的信息去生成一个RefrenceBean对象
        registerReferenceAnnotationBeanPostProcessor(registry);

    }

    //核心方法1，注册一个对@Service注解处理的 BeanDefinitionRegistryPostProcessor
    private void registerServiceAnnotationBeanPostProcessor(Set packagesToScan, BeanDefinitionRegistry registry) {
        // 生成一个RootBeanDefinition，对应的beanClass为ServiceAnnotationBeanPostProcessor.class
        BeanDefinitionBuilder builder = rootBeanDefinition(ServiceAnnotationBeanPostProcessor.class);
        // 将包路径作为在构造ServiceAnnotationBeanPostProcessor时调用构造方法时的传入参数
        builder.addConstructorArgValue(packagesToScan);
        builder.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
        AbstractBeanDefinition beanDefinition = builder.getBeanDefinition();
        BeanDefinitionReaderUtils.registerWithGeneratedName(beanDefinition, registry);

    }

    //核心方法2，注册一个对属性赋值处理的AnnotationInjectedBeanPostProcessor且带有ApplicationListener事件监听功能
    private void registerReferenceAnnotationBeanPostProcessor(BeanDefinitionRegistry registry) {

        // Register @Reference Annotation Bean Processor
        // 注册一个ReferenceAnnotationBeanPostProcessor做为bean，ReferenceAnnotationBeanPostProcessor是一个BeanPostProcessor
        BeanRegistrar.registerInfrastructureBean(registry,ReferenceAnnotationBeanPostProcessor.BEAN_NAME, ReferenceAnnotationBeanPostProcessor.class);

    }

    private Set getPackagesToScan(AnnotationMetadata metadata) {
        AnnotationAttributes attributes = AnnotationAttributes.fromMap(
                metadata.getAnnotationAttributes(DubboComponentScan.class.getName()));
        String[] basePackages = attributes.getStringArray("basePackages");
        Class[] basePackageClasses = attributes.getClassArray("basePackageClasses");
        String[] value = attributes.getStringArray("value");
        // Appends value array attributes
        Set packagesToScan = new LinkedHashSet(Arrays.asList(value));
        packagesToScan.addAll(Arrays.asList(basePackages));
        for (Class basePackageClass : basePackageClasses) {
            packagesToScan.add(ClassUtils.getPackageName(basePackageClass));
        }
        if (packagesToScan.isEmpty()) {
            return Collections.singleton(ClassUtils.getPackageName(metadata.getClassName()));
        }
        return packagesToScan;
    }

}

 

　　【4】扫描@Service注解，并且进行处理

　　　　汇总说明：实际上便是通过处理器扫描@Service注解的类，生成两个Bean【类对应的普通Bean，与Dubbo中要用到的ServiceBean】

　　　　其中ServiceBean，是先根据注解上的信息填充对应的属性，后采用环境变量中获取配置的属性，来完成属性填充。

public class ServiceAnnotationBeanPostProcessor implements BeanDefinitionRegistryPostProcessor, EnvironmentAware,ResourceLoaderAware, BeanClassLoaderAware {

    ...
    //核心方法1
    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {

        Set resolvedPackagesToScan = resolvePackagesToScan(packagesToScan);

        if (!CollectionUtils.isEmpty(resolvedPackagesToScan)) {
            // 扫描包，进行Bean注册，核心方法2调用
            registerServiceBeans(resolvedPackagesToScan, registry);
        } else {
            if (logger.isWarnEnabled()) {
                logger.warn("packagesToScan is empty , ServiceBean registry will be ignored!");
            }
        }

    }


    //核心方法2
    private void registerServiceBeans(Set packagesToScan, BeanDefinitionRegistry registry) {

        DubboClassPathBeanDefinitionScanner scanner = new DubboClassPathBeanDefinitionScanner(registry, environment, resourceLoader);

        BeanNameGenerator beanNameGenerator = resolveBeanNameGenerator(registry);

        scanner.setBeanNameGenerator(beanNameGenerator);

        // 扫描被Service注解标注的类
        scanner.addIncludeFilter(new AnnotationTypeFilter(Service.class));
        scanner.addIncludeFilter(new AnnotationTypeFilter(com.alibaba.dubbo.config.annotation.Service.class));

        for (String packageToScan : packagesToScan) {

            // Registers @Service Bean first
            // 扫描Dubbo自定义的@Service注解
            scanner.scan(packageToScan);

            // 查找被@Service注解的类的BeanDefinition（无论这个类有没有被@ComponentScan注解标注了）
            Set beanDefinitionHolders = findServiceBeanDefinitionHolders(scanner, packageToScan, registry, beanNameGenerator);

            if (!CollectionUtils.isEmpty(beanDefinitionHolders)) {

                // 扫描到BeanDefinition开始处理它，核心方法3的调用
                for (BeanDefinitionHolder beanDefinitionHolder : beanDefinitionHolders) {
                    registerServiceBean(beanDefinitionHolder, registry, scanner);
                }

                if (logger.isInfoEnabled()) { logger.info(b...); }
            } else {
                if (logger.isWarnEnabled()) { logger.warn(...); }
            }

        }

    }

    //核心方法3
    private void registerServiceBean(BeanDefinitionHolder beanDefinitionHolder, BeanDefinitionRegistry registry, DubboClassPathBeanDefinitionScanner scanner) {
        // 处理扫描到的每一个BeanDefinition
        // 1. 得到@Service注解上所配置的参数
        // 2. 根据每一个BeanDefinition会再额外的生成一个ServiceBean
        // 3. 对于每一个被@Service注解的类（服务的实现类），会生成两个Bean，一个服务实现类对应的Bean（普通Bean，和@Component一样），一个ServiceBean（Dubbo中要用到的Bean，因为在ServiceBean中包括了很的Config）

        // 具体的服务实现类
        Class beanClass = resolveClass(beanDefinitionHolder);
        // @Service可以对服务进行各种配置
        Annotation service = findServiceAnnotation(beanClass);

        AnnotationAttributes serviceAnnotationAttributes = getAnnotationAttributes(service, false, false);

        // 服务实现类对应的接口
        Class interfaceClass = resolveServiceInterfaceClass(serviceAnnotationAttributes, beanClass);
        // 服务实现类对应的bean的名字，比如：demoServiceImpl
        String annotatedServiceBeanName = beanDefinitionHolder.getBeanName();

        // 生成一个ServiceBean，核心方法4的调用
        AbstractBeanDefinition serviceBeanDefinition = buildServiceBeanDefinition(service, serviceAnnotationAttributes, interfaceClass, annotatedServiceBeanName);

        // ServiceBean Bean name   ServiceBean表示服务，我们要使用一个服务应该拿ServiceBean
        String beanName = generateServiceBeanName(serviceAnnotationAttributes, interfaceClass);

        if (scanner.checkCandidate(beanName, serviceBeanDefinition)) { // check duplicated candidate bean

            // 把ServiceBean注册进去，对应的beanName为ServiceBean:org.apache.dubbo.demo.DemoService
            registry.registerBeanDefinition(beanName, serviceBeanDefinition);

            if (logger.isInfoEnabled()) { logger.info(..); }
        } else {
            if (logger.isWarnEnabled()) { logger.warn(...); }
        }
    }

...

    //核心方法4
    private AbstractBeanDefinition buildServiceBeanDefinition(Annotation serviceAnnotation,AnnotationAttributes serviceAnnotationAttributes,Class interfaceClass,String annotatedServiceBeanName) {
        // 生成一个ServiceBean对应的BeanDefinition
        BeanDefinitionBuilder builder = rootBeanDefinition(ServiceBean.class);

        AbstractBeanDefinition beanDefinition = builder.getBeanDefinition();

        MutablePropertyValues propertyValues = beanDefinition.getPropertyValues();

        String[] ignoreAttributeNames = of("provider", "monitor", "application", "module", "registry", "protocol",
                "interface", "interfaceName", "parameters");

        // 把serviceAnnotation中的参数值赋值给ServiceBean的属性
        // 如：@Service(test = "test") 
        propertyValues.addPropertyValues(new AnnotationPropertyValuesAdapter(serviceAnnotation, environment, ignoreAttributeNames));

        // References "ref" property to annotated-@Service Bean
        // 如：@Service(protocol = "P1")，这种就是要根据对应的值找到对应的P1的config对象里面的值
        // ref属性赋值为另外一个bean, 对应的就是被@Service注解的服务实现类对应的bean
        addPropertyReference(builder, "ref", annotatedServiceBeanName);

        // Set interface
        builder.addPropertyValue("interface", interfaceClass.getName());
        // Convert parameters into map
        builder.addPropertyValue("parameters", convertParameters(serviceAnnotationAttributes.getStringArray("parameters")));

        // 配置了methods属性，则给ServiceBean对应的methods属性赋值
        // Add methods parameters
        List methodConfigs = convertMethodConfigs(serviceAnnotationAttributes.get("methods"));
        if (!methodConfigs.isEmpty()) {
            builder.addPropertyValue("methods", methodConfigs);
        }

        /**
         * Add {@link org.apache.dubbo.config.ProviderConfig} Bean reference
         */
        String providerConfigBeanName = serviceAnnotationAttributes.getString("provider");
        if (StringUtils.hasText(providerConfigBeanName)) {
            addPropertyReference(builder, "provider", providerConfigBeanName);
        }

        /**
         * Add {@link org.apache.dubbo.config.MonitorConfig} Bean reference
         */
        String monitorConfigBeanName = serviceAnnotationAttributes.getString("monitor");
        if (StringUtils.hasText(monitorConfigBeanName)) {
            addPropertyReference(builder, "monitor", monitorConfigBeanName);
        }

        /**
         * Add {@link org.apache.dubbo.config.ApplicationConfig} Bean reference
         */
        String applicationConfigBeanName = serviceAnnotationAttributes.getString("application");
        if (StringUtils.hasText(applicationConfigBeanName)) {
            addPropertyReference(builder, "application", applicationConfigBeanName);
        }

        /**
         * Add {@link org.apache.dubbo.config.ModuleConfig} Bean reference
         */
        String moduleConfigBeanName = serviceAnnotationAttributes.getString("module");
        if (StringUtils.hasText(moduleConfigBeanName)) {
            addPropertyReference(builder, "module", moduleConfigBeanName);
        }


        /**
         * Add {@link org.apache.dubbo.config.RegistryConfig} Bean reference
         * 获取注解上配置的注册中心的beanName
         */
        String[] registryConfigBeanNames = serviceAnnotationAttributes.getStringArray("registry");

        List registryRuntimeBeanReferences = toRuntimeBeanReferences(registryConfigBeanNames);

        if (!registryRuntimeBeanReferences.isEmpty()) {
            builder.addPropertyValue("registries", registryRuntimeBeanReferences);
        }

        /**
         * Add {@link org.apache.dubbo.config.ProtocolConfig} Bean reference
         */
        String[] protocolConfigBeanNames = serviceAnnotationAttributes.getStringArray("protocol");

        List protocolRuntimeBeanReferences = toRuntimeBeanReferences(protocolConfigBeanNames);

        if (!protocolRuntimeBeanReferences.isEmpty()) {
            builder.addPropertyValue("protocols", protocolRuntimeBeanReferences);
        }

        return builder.getBeanDefinition();

    }
....
}

 

　　【5】扫描@Reference注解，并且进行处理

　　　　1）ReferenceAnnotationBeanPostProcessor类会被调用是基于继承关系

//class ReferenceAnnotationBeanPostProcessor extends AnnotationInjectedBeanPostProcessor
//abstract class AnnotationInjectedBeanPostProcessor extends InstantiationAwareBeanPostProcessorAdapter 
//InstantiationAwareBeanPostProcessorAdapter类便是属性注入时候会调用的
//调用AnnotationInjectedBeanPostProcessor抽象类的postProcessPropertyValues方法
@Override
public PropertyValues postProcessPropertyValues(
        PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeanCreationException {

    // 寻找需要注入的属性（被@Reference标注的Field）
    InjectionMetadata metadata = findInjectionMetadata(beanName, bean.getClass(), pvs);
    try {
        metadata.inject(bean, beanName, pvs);
    } catch (BeanCreationException ex) {
        throw ex;
    } catch (Throwable ex) {
        throw new BeanCreationException(beanName, "Injection of @" + getAnnotationType().getSimpleName()
                + " dependencies is failed", ex);
    }
    return pvs;
}

//最终走回到ReferenceAnnotationBeanPostProcessor类的doGetInjectedBean方法

 

　　　　2）ReferenceAnnotationBeanPostProcessor中的方法

public class ReferenceAnnotationBeanPostProcessor extends AnnotationInjectedBeanPostProcessor implements ApplicationContextAware, ApplicationListener {
...
    // 该方法得到的对象会赋值给@ReferenceBean注解的属性
    @Override
    protected Object doGetInjectedBean(AnnotationAttributes attributes, Object bean, String beanName, Class injectedType,InjectionMetadata.InjectedElement injectedElement) throws Exception {

        // 得到引入服务的beanName
        // attributes里存的是@Reference注解中的所配置的属性与值
        // injectedType表示引入的是哪个服务接口
        // referencedBeanName的值为  ServiceBean:org.apache.dubbo.demo.DemoService  表示得到该服务Bean的beanName
        // referencedBeanName表示 我现在要引用的这个服务，它导出时对应的ServiceBean的beanName是什么，可以用来判断现在我引用的这个服务是不是我自己导出的
        String referencedBeanName = buildReferencedBeanName(attributes, injectedType);


        // @Reference(methods=[Lorg.apache.dubbo.config.annotation.Method;@39b43d60) org.apache.dubbo.demo.DemoService
        // 我要生成一个RefrenceBean，对应的beanName， 根据@Reference注解来标识不同
        String referenceBeanName = getReferenceBeanName(attributes, injectedType);

        // 生成一个ReferenceBean对象，方法1
        ReferenceBean referenceBean = buildReferenceBeanIfAbsent(referenceBeanName, attributes, injectedType);

        // 把referenceBean添加到Spring容器中去，方法2
        registerReferenceBean(referencedBeanName, referenceBean, attributes, injectedType);

        cacheInjectedReferenceBean(referenceBean, injectedElement);

        // 创建一个代理对象，Service中的属性被注入的就是这个代理对象
        // 内部会调用referenceBean.get(); ，核心方法1
        return getOrCreateProxy(referencedBeanName, referenceBeanName, referenceBean, injectedType);
    }

    //方法1
    private ReferenceBean buildReferenceBeanIfAbsent(String referenceBeanName, AnnotationAttributes attributes, Class referencedType) throws Exception {

        ReferenceBean referenceBean = referenceBeanCache.get(referenceBeanName);

        if (referenceBean == null) {

            // 生成了一个ReferenceBean对象，attributes是@Reference注解的参数值
            ReferenceBeanBuilder beanBuilder = ReferenceBeanBuilder
                    .create(attributes, applicationContext)
                    .interfaceClass(referencedType);
            referenceBean = beanBuilder.build();

            referenceBeanCache.put(referenceBeanName, referenceBean);
        } else if (!referencedType.isAssignableFrom(referenceBean.getInterfaceClass())) {
            throw new IllegalArgumentException(...);
        }
        return referenceBean;
    }

    //方法2
    private void registerReferenceBean(String referencedBeanName, ReferenceBean referenceBean, AnnotationAttributes attributes, Class interfaceClass) {

        ConfigurableListableBeanFactory beanFactory = getBeanFactory();

        // @Reference(parameters=[Ljava.lang.String;@72ef8d15) org.apache.dubbo.demo.DemoService
        // ReferenceBean的beanName，注意这个beanName，它是直接取的@Reference的全信息
        // 所以，就算引用的是同一个服务，如果@Reference注解上的信息不同，那么就会生成不同的ReferenceBean
        String beanName = getReferenceBeanName(attributes, interfaceClass);

        // 要引入的服务就是本地提供的一个服务
        if (existsServiceBean(referencedBeanName)) { // If @Service bean is local one
            /**
             * Get  the @Service's BeanDefinition from {@link BeanFactory}
             * Refer to {@link ServiceAnnotationBeanPostProcessor#buildServiceBeanDefinition}
             */
            AbstractBeanDefinition beanDefinition = (AbstractBeanDefinition) beanFactory.getBeanDefinition(referencedBeanName);
            RuntimeBeanReference runtimeBeanReference = (RuntimeBeanReference) beanDefinition.getPropertyValues().get("ref"); // ServiceBean --- ref
            // The name of bean annotated @Service
            String serviceBeanName = runtimeBeanReference.getBeanName();
            // register Alias rather than a new bean name, in order to reduce duplicated beans
            // 如果是本地提供的一个服务，那么就@Reference(parameters=[Ljava.lang.String;@72ef8d15) org.apache.dubbo.demo.DemoService
            // 的别名是demoService，不需要是ServiceBean的名字
            beanFactory.registerAlias(serviceBeanName, beanName);
        } else { // Remote @Service Bean
            if (!beanFactory.containsBean(beanName)) {
                beanFactory.registerSingleton(beanName, referenceBean);
            }
        }
    }

    //核心方法1
    //这里面其实有点绕，因为@Reference其实也相当于做了@Autowired的工作
    //能在本地找到，如果不代理的话其实相当于@Autowired注入属性（不会走Dubbo的逻辑），所以包装成代理，让它也走Dubbo的逻辑
    private Object getOrCreateProxy(String referencedBeanName, String referenceBeanName, ReferenceBean referenceBean, Class serviceInterfaceType) {
        //这个其实是判断本地有没有
        if (existsServiceBean(referencedBeanName)) { // If the local @Service Bean exists, build a proxy of ReferenceBean
            //进行代理，让它走Dubbo的逻辑
            return newProxyInstance(getClassLoader(), new Class[]{serviceInterfaceType}, wrapInvocationHandler(referenceBeanName, referenceBean));
        } else {                                    // ReferenceBean should be initialized and get immediately
            // 重点，服务引入的地方
            return referenceBean.get();
        }
    }

...
}

 

　　【6】图示：

 　　　　

 

Dubbo服务导出

　　【0】服务导出要做的几件事情：

1. 确定服务的参数
2. 确定服务支持的协议
3. 构造服务最终的URL
4. 将服务URL注册到注册中心去
5. 根据服务支持的不同协议，启动不同的Server，用来接收和处理请求
6. 因为Dubbo支持动态配置服务参数，所以服务导出时还需要绑定一个监听器Listener来监听服务的参数是否有修改，如果发现有修改，则需要重新进行导出

　　【1】核心点记录

ServiceBean的两种暴露服务的方法
1.利用InitializingBean接口，调用export()方法（没有监听器的情况下才行）
2.利用监听ContextRefreshedEvent事件达到服务暴露

动态代理生成 Invoker 包装成 wrapperInvoker

  RegistryProtocol进行注册
  DubboProtocol对 Invoker 进行导出，返回一个Exporter

　ExchangeServer

 

　　【2】ServiceBean是怎么进程服务导出的

//1是利用InitializingBean接口，调用export()方法【主要是调用父类的export()方法和发布ServiceBeanExportedEvent事件】
//2是利用监听ContextRefreshedEvent事件达到服务暴露
public class ServiceBean extends ServiceConfig implements InitializingBean, DisposableBean, ApplicationContextAware, ApplicationListener, BeanNameAware, ApplicationEventPublisherAware {

....

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) {
        this.applicationContext = applicationContext;

        // 如果某一个Service是通过Spring暴露的，
        // 那么当需要获取该服务时就要从Spring容器中进行获取，
        // 也就是从applicationContext中获取，所以需要把applicationContext添加到SpringExtensionFactory中去
        SpringExtensionFactory.addApplicationContext(applicationContext);
        // 一定要有这一步，不然ServiceBean将接收不到ContextRefreshedEvent事件
        supportedApplicationListener = addApplicationListener(applicationContext, this);
    }

    //当接收到监听ContextRefreshedEvent事件时候
    @Override
    public void onApplicationEvent(ContextRefreshedEvent event) {
        // 当前服务没有被导出并且没有卸载，才导出服务
        if (!isExported() && !isUnexported()) {
            if (logger.isInfoEnabled()) {
                logger.info("The service ready on spring started. service: " + getInterface());
            }
            // 服务导出（服务注册）
            export();
        }
    }

    @Override
    @SuppressWarnings({"unchecked", "deprecation"})
    public void afterPropertiesSet() throws Exception {

        // 如果@Service中没有配置provider
        if (getProvider() == null) {
            // 就从Spring容器中找ProviderConfig类型的Bean
            Map providerConfigMap = applicationContext == null ? null : BeanFactoryUtils.beansOfTypeIncludingAncestors(applicationContext, ProviderConfig.class, false, false);
            if (providerConfigMap != null && providerConfigMap.size() > 0) {
                // 从Spring容器中找ProtocolConfig类型的Bean
                Map protocolConfigMap = applicationContext == null ? null : BeanFactoryUtils.beansOfTypeIncludingAncestors(applicationContext, ProtocolConfig.class, false, false);

                // 如果存在ProtocolConfig存在，并且存在多个ProviderConfig
                if (CollectionUtils.isEmptyMap(protocolConfigMap) && providerConfigMap.size() > 1) { // backward compatibility

                    // 如果找到多个，取第一个default等于true的ProviderConfig
                    List providerConfigs = new ArrayList();
                    for (ProviderConfig config : providerConfigMap.values()) {
                        if (config.isDefault() != null && config.isDefault()) {
                            providerConfigs.add(config);
                        }
                    }
                    if (!providerConfigs.isEmpty()) {
                        setProviders(providerConfigs);
                    }
                } else {
                    ProviderConfig providerConfig = null;
                    for (ProviderConfig config : providerConfigMap.values()) {
                        if (config.isDefault() == null || config.isDefault()) {
                            if (providerConfig != null) {
                                throw new IllegalStateException(...);
                            }
                            providerConfig = config;
                        }
                    }
                    if (providerConfig != null) {
                        setProvider(providerConfig);
                    }
                }
            }
        }
        if (getApplication() == null && (getProvider() == null || getProvider().getApplication() == null)) {
            Map applicationConfigMap = applicationContext == null ? null : BeanFactoryUtils.beansOfTypeIncludingAncestors(applicationContext, ApplicationConfig.class, false, false);
            if (applicationConfigMap != null && applicationConfigMap.size() > 0) {
                ApplicationConfig applicationConfig = null;
                for (ApplicationConfig config : applicationConfigMap.values()) {
                    if (applicationConfig != null) {
                        throw new IllegalStateException(...);
                    }
                    applicationConfig = config;
                }
                if (applicationConfig != null) {
                    setApplication(applicationConfig);
                }
            }
        }
        if (getModule() == null && (getProvider() == null || getProvider().getModule() == null)) {
            Map moduleConfigMap = applicationContext == null ? null : BeanFactoryUtils.beansOfTypeIncludingAncestors(applicationContext, ModuleConfig.class, false, false);
            if (moduleConfigMap != null && moduleConfigMap.size() > 0) {
                ModuleConfig moduleConfig = null;
                for (ModuleConfig config : moduleConfigMap.values()) {
                    if (config.isDefault() == null || config.isDefault()) {
                        if (moduleConfig != null) {
                            throw new IllegalStateException(...);
                        }
                        moduleConfig = config;
                    }
                }
                if (moduleConfig != null) {
                    setModule(moduleConfig);
                }
            }
        }

        // registryIds代码能看到，但是没找到在哪里能配置
        if (StringUtils.isEmpty(getRegistryIds())) {
            if (getApplication() != null && StringUtils.isNotEmpty(getApplication().getRegistryIds())) {
                setRegistryIds(getApplication().getRegistryIds());
            }
            if (getProvider() != null && StringUtils.isNotEmpty(getProvider().getRegistryIds())) {
                setRegistryIds(getProvider().getRegistryIds());
            }
        }

        if ((CollectionUtils.isEmpty(getRegistries())) && (getProvider() == null || CollectionUtils.isEmpty(getProvider().getRegistries())) && (getApplication() == null || CollectionUtils.isEmpty(getApplication().getRegistries()))) {
            Map registryConfigMap = applicationContext == null ? null : BeanFactoryUtils.beansOfTypeIncludingAncestors(applicationContext, RegistryConfig.class, false, false);
            if (CollectionUtils.isNotEmptyMap(registryConfigMap)) {
                List registryConfigs = new ArrayList<>();
                if (StringUtils.isNotEmpty(registryIds)) {
                    Arrays.stream(COMMA_SPLIT_PATTERN.split(registryIds)).forEach(id -> {
                        if (registryConfigMap.containsKey(id)) {
                            registryConfigs.add(registryConfigMap.get(id));
                        }
                    });
                }

                if (registryConfigs.isEmpty()) {
                    for (RegistryConfig config : registryConfigMap.values()) {
                        if (StringUtils.isEmpty(registryIds) && (config.isDefault() == null || config.isDefault().booleanValue())) {
                            registryConfigs.add(config);
                        }
                    }
                }
                if (!registryConfigs.isEmpty()) {
                    super.setRegistries(registryConfigs);
                }
            }
        }
        if (getMetadataReportConfig() == null) {
            Map metadataReportConfigMap = applicationContext == null ? null : BeanFactoryUtils.beansOfTypeIncludingAncestors(applicationContext, MetadataReportConfig.class, false, false);
            if (metadataReportConfigMap != null && metadataReportConfigMap.size() == 1) {
                super.setMetadataReportConfig(metadataReportConfigMap.values().iterator().next());
            } else if (metadataReportConfigMap != null && metadataReportConfigMap.size() > 1) {
                throw new IllegalStateException("Multiple MetadataReport configs: " + metadataReportConfigMap);
            }
        }

        if (getConfigCenter() == null) {
            Map configenterMap = applicationContext == null ? null : BeanFactoryUtils.beansOfTypeIncludingAncestors(applicationContext, ConfigCenterConfig.class, false, false);
            if (configenterMap != null && configenterMap.size() == 1) {
                super.setConfigCenter(configenterMap.values().iterator().next());
            } else if (configenterMap != null && configenterMap.size() > 1) {
                throw new IllegalStateException("Multiple ConfigCenter found:" + configenterMap);
            }
        }

        if (getMonitor() == null
                && (getProvider() == null || getProvider().getMonitor() == null)
                && (getApplication() == null || getApplication().getMonitor() == null)) {
            Map monitorConfigMap = applicationContext == null ? null : BeanFactoryUtils.beansOfTypeIncludingAncestors(applicationContext, MonitorConfig.class, false, false);
            if (monitorConfigMap != null && monitorConfigMap.size() > 0) {
                MonitorConfig monitorConfig = null;
                for (MonitorConfig config : monitorConfigMap.values()) {
                    if (config.isDefault() == null || config.isDefault()) {
                        if (monitorConfig != null) {
                            throw new IllegalStateException("Duplicate monitor configs: " + monitorConfig + " and " + config);
                        }
                        monitorConfig = config;
                    }
                }
                if (monitorConfig != null) {
                    setMonitor(monitorConfig);
                }
            }
        }

        if (getMetrics() == null) {
            Map metricsConfigMap = applicationContext == null ? null : BeanFactoryUtils.beansOfTypeIncludingAncestors(applicationContext, MetricsConfig.class, false, false);
            if (metricsConfigMap != null && metricsConfigMap.size() > 0) {
                MetricsConfig metricsConfig = null;
                for (MetricsConfig config : metricsConfigMap.values()) {
                    if (metricsConfig != null) {
                        throw new IllegalStateException("Duplicate metrics configs: " + metricsConfig + " and " + config);
                    }
                    metricsConfig = config;
                }
                if (metricsConfig != null) {
                    setMetrics(metricsConfig);
                }
            }
        }

        // protocolIds也没看到在哪里配置
        if (StringUtils.isEmpty(getProtocolIds())) {
            if (getProvider() != null && StringUtils.isNotEmpty(getProvider().getProtocolIds())) {
                setProtocolIds(getProvider().getProtocolIds());
            }
        }

        if (CollectionUtils.isEmpty(getProtocols())
                && (getProvider() == null || CollectionUtils.isEmpty(getProvider().getProtocols()))) {
            Map protocolConfigMap = applicationContext == null ? null : BeanFactoryUtils.beansOfTypeIncludingAncestors(applicationContext, ProtocolConfig.class, false, false);
            if (protocolConfigMap != null && protocolConfigMap.size() > 0) {
                List protocolConfigs = new ArrayList();
                if (StringUtils.isNotEmpty(getProtocolIds())) {
                    Arrays.stream(COMMA_SPLIT_PATTERN.split(getProtocolIds()))
                            .forEach(id -> {
                                if (protocolConfigMap.containsKey(id)) {
                                    protocolConfigs.add(protocolConfigMap.get(id));
                                }
                            });
                }

                if (protocolConfigs.isEmpty()) {
                    for (ProtocolConfig config : protocolConfigMap.values()) {
                        if (StringUtils.isEmpty(protocolIds)) {
                            protocolConfigs.add(config);
                        }
                    }
                }

                if (!protocolConfigs.isEmpty()) {
                    super.setProtocols(protocolConfigs);
                }
            }
        }
        if (StringUtils.isEmpty(getPath())) {
            if (StringUtils.isNotEmpty(beanName)
                    && StringUtils.isNotEmpty(getInterface())
                    && beanName.startsWith(getInterface())) {
                setPath(beanName);
            }
        }
        //没有监听事件才做暴露服务
        if (!supportedApplicationListener) {
            export();
        }
    }


    //服务暴露的核心方法
    @Override
    public void export() {
        super.export();
        // Publish ServiceBeanExportedEvent
        publishExportEvent();
    }

    private void publishExportEvent() {
        ServiceBeanExportedEvent exportEvent = new ServiceBeanExportedEvent(this);
        applicationEventPublisher.publishEvent(exportEvent);
    }

    @Override
    public void setApplicationEventPublisher(ApplicationEventPublisher applicationEventPublisher) {
        this.applicationEventPublisher = applicationEventPublisher;
    }
}

　　　　1）ServiceConfig类#export()方法

public synchronized void export() {
    //读取配置并补全（最新最全的配置），方法1
    checkAndUpdateSubConfigs();

    // 检查服务是否需要导出
    if (!shouldExport()) {
        return;
    }

    // 检查是否需要延迟发布
    if (shouldDelay()) {
        DELAY_EXPORT_EXECUTOR.schedule(this::doExport, getDelay(), TimeUnit.MILLISECONDS);
    } else {
        // 导出服务，方法2
        doExport();
    }
}

 

　　　　2）方法1：ServiceConfig类#checkAndUpdateSubConfigs()方法

/**
 * 1. ServiceConfig中的某些属性如果是空的，那么就从ProviderConfig、ModuleConfig、ApplicationConfig中获取
 * 2. 从配置中心获取配置，包括应用配置和全局配置
 * 3. 从配置中心获取Provider配置
 * 4. 从配置中心获取Protocol配置
 * 5. 如果ApplicationConfig为空，则构造一个ApplicationConfig
 * 6. 从配置中心获取Registry配置
 * 7. 更新ServiceConfig中的属性为优先级最高的配置
 * 8. 更新MetadataReportConfig中的属性为优先级最高的配置
 * 9. 检查当前服务是不是一个泛化服务
 * 10.检查Stub和Local
 * 11.检查Mock
 */
public void checkAndUpdateSubConfigs() {
// ServiceConfig中的某些属性如果是空的，那么就从ProviderConfig、ModuleConfig、ApplicationConfig中获取（之前生成的配置Bean）
    completeCompoundConfigs();

    // 方法1.1
    // 从配置中心获取配置，包括应用配置和全局配置
    // 把获取到的配置放入到Environment中的externalConfigurationMap和appExternalConfigurationMap中
    // 并刷新所有的Config属性
    startConfigCenter();

    // 如果没有ProviderConfig对象，则创建一个
    checkDefault();

    // 如果没有单独的配置protocols，那么就从provider获取配置的协议，添加到的ServiceConfig中去
    // 假如程序员在配置文件中配了一个dubbo协议，配置中心的全局配置或应用配置中也配置了一个协议，那么就会被添加到ServiceConfig中
    checkProtocol();

    checkApplication();

    // if protocol is not injvm checkRegistry
    // 如果protocol不是只有injvm协议，表示服务调用不是只在本机jvm里面调用，那就需要用到注册中心
    // 如果protocol是injvm，表示本地调用
    if (!isOnlyInJvm()) {
        checkRegistry();
    }

    // 刷新ServiceConfig，方法1.2
    this.refresh();

    // 如果配了metadataReportConfig，那么就刷新配置
    checkMetadataReport();

    if (StringUtils.isEmpty(interfaceName)) {
        throw new IllegalStateException(" interface not allow null!");
    }

    // 当前服务对应的实现类是一个GenericService，表示没有特定的接口
    if (ref instanceof GenericService) {
        interfaceClass = GenericService.class;
        if (StringUtils.isEmpty(generic)) {
            generic = Boolean.TRUE.toString();
        }
    } else {
        // 加载接口
        try {
            interfaceClass = Class.forName(interfaceName, true, Thread.currentThread()
                    .getContextClassLoader());
        } catch (ClassNotFoundException e) {
            throw new IllegalStateException(e.getMessage(), e);
        }
        // 刷新MethodConfig，并判断MethodConfig中对应的方法在接口中是否存在
        checkInterfaceAndMethods(interfaceClass, methods);
        // 实现类是不是该接口类型
        checkRef();
        generic = Boolean.FALSE.toString();
    }
    // local和stub一样，不建议使用了
    if (local != null) {
        // 如果本地存根为true，则存根类为interfaceName + "Local"
        if (Boolean.TRUE.toString().equals(local)) {
            local = interfaceName + "Local";
        }
        // 加载本地存根类
        Class localClass;
        try {
            localClass = ClassUtils.forNameWithThreadContextClassLoader(local);
        } catch (ClassNotFoundException e) {
            throw new IllegalStateException(e.getMessage(), e);
        }
        if (!interfaceClass.isAssignableFrom(localClass)) {
            throw new IllegalStateException("The local implementation class " + localClass.getName() + " not implement interface " + interfaceName);
        }
    }
    // 本地存根
    if (stub != null) {
        // 如果本地存根为true，则存根类为interfaceName + "Stub"
        if (Boolean.TRUE.toString().equals(stub)) {
            stub = interfaceName + "Stub";
        }
        Class stubClass;
        try {
            stubClass = ClassUtils.forNameWithThreadContextClassLoader(stub);
        } catch (ClassNotFoundException e) {
            throw new IllegalStateException(e.getMessage(), e);
        }
        if (!interfaceClass.isAssignableFrom(stubClass)) {
            throw new IllegalStateException("The stub implementation class " + stubClass.getName() + " not implement interface " + interfaceName);
        }
    }
    // 检查local和stub
    checkStubAndLocal(interfaceClass);
    // 检查mock
    checkMock(interfaceClass);
}

 

　　　　3）方法1.1，AbstractInterfaceConfig类#startConfigCenter()方法

void startConfigCenter() {
    if (configCenter == null) {
        ConfigManager.getInstance().getConfigCenter().ifPresent(cc -> this.configCenter = cc);
    }
    // 如果配置了ConfigCenter
    if (this.configCenter != null) {
        // 从其他位置获取配置中心的相关属性信息，比如配置中心地址
        // TODO there may have duplicate refresh
        this.configCenter.refresh();

        // 属性更新后，从远程配置中心获取数据(应用配置，全局配置)
        prepareEnvironment();
    }
    // 从配置中心取到配置数据后，刷新所有的XxConfig中的属性
    ConfigManager.getInstance().refreshAll();
}

private void prepareEnvironment() {
    if (configCenter.isValid()) {
        if (!configCenter.checkOrUpdateInited()) {
            return;
        }

        // 动态配置中心，管理台上的配置中心
        DynamicConfiguration dynamicConfiguration = getDynamicConfiguration(configCenter.toUrl());

        // 如果是zookeeper，获取的就是/dubbo/config/dubbo/dubbo.properties节点中的内容
        String configContent = dynamicConfiguration.getProperties(configCenter.getConfigFile(), configCenter.getGroup());

        String appGroup = application != null ? application.getName() : null;
        String appConfigContent = null;
        if (StringUtils.isNotEmpty(appGroup)) {
            // 获取的就是/dubbo/config/dubbo-demo-consumer-application/dubbo.properties节点中的内容
            // 这里有bug
            appConfigContent = dynamicConfiguration.getProperties (StringUtils.isNotEmpty(configCenter.getAppConfigFile()) ? configCenter.getAppConfigFile() : configCenter.getConfigFile(), appGroup );
        }
        try {
            Environment.getInstance().setConfigCenterFirst(configCenter.isHighestPriority());
            Environment.getInstance().updateExternalConfigurationMap(parseProperties(configContent));
            Environment.getInstance().updateAppExternalConfigurationMap(parseProperties(appConfigContent));
        } catch (IOException e) {
            throw new IllegalStateException(...);
        }
    }
}

 

　　　　4）方法1.2，AbstractInterfaceConfig类#refresh()方法

// 刷新XxConfig
// 一个XxConfig对象的属性可能是有值的，也可能是没有值的，这时需要从其他位置获取属性值,来进行属性的覆盖
// 覆盖的优先级，从大到小为系统变量->配置中心应用配置->配置中心全局配置->注解或xml中定义->dubbo.properties文件
// 以ServiceConfig为例，ServiceConfig中包括很多属性，比如timeout
// 但是在定义一个Service时，如果在注解上没有配置timeout，那么就会其他地方获取timeout的配置
// 比如可以从系统变量->配置中心应用配置->配置中心全局配置->注解或xml中定义->dubbo.properties文件
// refresh是刷新，将当前ServiceConfig上的set方法所对应的属性更新为优先级最高的值
public void refresh() {
    try {
        CompositeConfiguration compositeConfiguration = Environment.getInstance().getConfiguration(getPrefix(), getId());

        // 表示XxConfig对象本身- AbstractConfig
        Configuration config = new ConfigConfigurationAdapter(this);

        //设置顺序，
        if (Environment.getInstance().isConfigCenterFirst()) {
            // The sequence would be: SystemConfiguration -> AppExternalConfiguration -> ExternalConfiguration -> AbstractConfig -> PropertiesConfiguration
            compositeConfiguration.addConfiguration(4, config);
        } else {
            // The sequence would be: SystemConfiguration -> AbstractConfig -> AppExternalConfiguration -> ExternalConfiguration -> PropertiesConfiguration
            compositeConfiguration.addConfiguration(2, config);
        }

        // loop methods, get override value and set the new value back to method
        //
        Method[] methods = getClass().getMethods();
        for (Method method : methods) {
            // 是不是setXX()方法
            if (MethodUtils.isSetter(method)) {
                // 获取xx配置项的value
                String value = StringUtils.trim(compositeConfiguration.getString(extractPropertyName(getClass(), method)));
                // isTypeMatch() is called to avoid duplicate and incorrect update, for example, we have two 'setGeneric' methods in ReferenceConfig.
                if (StringUtils.isNotEmpty(value) && ClassUtils.isTypeMatch(method.getParameterTypes()[0], value)) {
                    method.invoke(this, ClassUtils.convertPrimitive(method.getParameterTypes()[0], value));
                }
              // 是不是setParameters()方法
            } else if (isParametersSetter(method)) {
                // 获取parameter配置项的value
                String value = StringUtils.trim(compositeConfiguration.getString(extractPropertyName(getClass(), method)));
                if (StringUtils.isNotEmpty(value)) {
                    Map map = invokeGetParameters(getClass(), this);
                    map = map == null ? new HashMap<>() : map;
                    map.putAll(convert(StringUtils.parseParameters(value), ""));
                    invokeSetParameters(getClass(), this, map);
                }
            }
        }
    } catch (Exception e) {
        logger.error("Failed to override ", e);
    }
}

public CompositeConfiguration getConfiguration(String prefix, String id) {
    CompositeConfiguration compositeConfiguration = new CompositeConfiguration();
    // Config center has the highest priority

    // JVM环境变量
    compositeConfiguration.addConfiguration(this.getSystemConfig(prefix, id));
    // 操作系统环境变量
    compositeConfiguration.addConfiguration(this.getEnvironmentConfig(prefix, id));

    // 配置中心APP配置
    compositeConfiguration.addConfiguration(this.getAppExternalConfig(prefix, id));

    // 配置中心Global配置
    compositeConfiguration.addConfiguration(this.getExternalConfig(prefix, id));

    // dubbo.properties中的配置
    compositeConfiguration.addConfiguration(this.getPropertiesConfig(prefix, id));
    return compositeConfiguration;
}

 

　　　　5）方法2，ServiceConfig类#doExport()方法

protected synchronized void doExport() {
    // 当前服务已经被取消了，就不能再导出了
    if (unexported) {
        throw new IllegalStateException(...);
    }
    // 已经导出了，就不再导出了
    if (exported) {
        return;
    }
    exported = true;

    if (StringUtils.isEmpty(path)) {
        path = interfaceName;
    }
    doExportUrls();
}

@SuppressWarnings({"unchecked", "rawtypes"})
private void doExportUrls() {
    // 得到url，注册服务也是一个服务，所以也会有对应的url，通过调用该url完成服务注册
    List registryURLs = loadRegistries(true);   //

    // 遍历每个协议
    // 一个协议一个服务
    for (ProtocolConfig protocolConfig : protocols) {
        // path表示服务名
        // contextPath表示应用名（可配置）
        // pathKey = group/contextpath/path:version
        // 例子：myGroup/user/org.apache.dubbo.demo.DemoService:1.0.1

        String pathKey = URL.buildKey(getContextPath(protocolConfig).map(p -> p + "/" + path).orElse(path), group, version);

        // ProviderModel中存在服务提供者访问路径，实现类，接口，以及接口中的各个方法对应的ProviderMethodModel
        // ProviderMethodModel表示某一个方法，方法名，所属的服务的，
        ProviderModel providerModel = new ProviderModel(pathKey, ref, interfaceClass);

        // ApplicationModel表示应用中有哪些服务提供者和引用了哪些服务
        ApplicationModel.initProviderModel(pathKey, providerModel);

        // 每种协议导出一个单独的服务,注册到各个注册中心
        doExportUrlsFor1Protocol(protocolConfig, registryURLs);
    }
}

 

　　　　6）doExportUrlsFor1Protocol方法

private void doExportUrlsFor1Protocol(ProtocolConfig protocolConfig, List registryURLs) {
    // protocolConfig表示某个协议，registryURLs表示所有的注册中心

    // 如果配置的某个协议，没有配置name，那么默认为dubbo
    String name = protocolConfig.getName();
    if (StringUtils.isEmpty(name)) {
        name = DUBBO;
    }

    // 这个map表示服务url的参数
    Map map = new HashMap();
    map.put(SIDE_KEY, PROVIDER_SIDE);

    appendRuntimeParameters(map);
    // 监控中心参数
    appendParameters(map, metrics);
    // 应用相关参数
    appendParameters(map, application);
    // 模块相关参数
    appendParameters(map, module);
    // 提供者相关参数
    appendParameters(map, provider);
    // 协议相关参数
    appendParameters(map, protocolConfig);
    // 服务本身相关参数
    appendParameters(map, this);

    // 服务中某些方法参数
    if (CollectionUtils.isNotEmpty(methods)) {
        for (MethodConfig method : methods) {
            // 某个方法的配置参数，注意有prefix
            appendParameters(map, method, method.getName());
            String retryKey = method.getName() + ".retry";

            // 如果某个方法配置存在xx.retry=false，则改成xx.retry=0
            if (map.containsKey(retryKey)) {
                String retryValue = map.remove(retryKey);
                if (Boolean.FALSE.toString().equals(retryValue)) {
                    map.put(method.getName() + ".retries", "0");
                }
            }
            List arguments = method.getArguments();
            if (CollectionUtils.isNotEmpty(arguments)) {
                // 遍历当前方法配置中的参数配置
                for (ArgumentConfig argument : arguments) {

                    // 如果配置了type，则遍历当前接口的所有方法，然后找到方法名和当前方法名相等的方法，可能存在多个
                    // 如果配置了index,则看index对应位置的参数类型是否等于type,如果相等，则向map中存入argument对象中的参数
                    // 如果没有配置index，那么则遍历方法所有的参数类型，等于type则向map中存入argument对象中的参数
                    // 如果没有配置type,但配置了index,则把对应位置的argument放入map
                    // convert argument type
                    if (argument.getType() != null && argument.getType().length() > 0) {
                        Method[] methods = interfaceClass.getMethods();
                        // visit all methods
                        if (methods != null && methods.length > 0) {
                            for (int i = 0; i < methods.length; i++) {
                                String methodName = methods[i].getName();
                                // target the method, and get its signature
                                if (methodName.equals(method.getName())) {
                                    Class[] argtypes = methods[i].getParameterTypes();
                                    // one callback in the method
                                    if (argument.getIndex() != -1) {
                                        if (argtypes[argument.getIndex()].getName().equals(argument.getType())) {
                                            appendParameters(map, argument, method.getName() + "." + argument.getIndex());
                                        } else {
                                            throw new IllegalArgumentException(...);
                                        }
                                    } else {
                                        // multiple callbacks in the method
                                        for (int j = 0; j < argtypes.length; j++) {
                                            Class argclazz = argtypes[j];
                                            if (argclazz.getName().equals(argument.getType())) {
                                                appendParameters(map, argument, method.getName() + "." + j);
                                                if (argument.getIndex() != -1 && argument.getIndex() != j) {
                                                    throw new IllegalArgumentException(...);
                                                }
                                            }
                                        }
                                    }
                                }
                            }
                        }
                    } else if (argument.getIndex() != -1) {
                        appendParameters(map, argument, method.getName() + "." + argument.getIndex());
                    } else {
                        throw new IllegalArgumentException(...);
                    }

                }
            }
        } // end of methods for
    }

    if (ProtocolUtils.isGeneric(generic)) {
        map.put(GENERIC_KEY, generic);
        map.put(METHODS_KEY, ANY_VALUE);
    } else {
        String revision = Version.getVersion(interfaceClass, version);
        if (revision != null && revision.length() > 0) {
            map.put(REVISION_KEY, revision);
        }

        // 通过接口对应的Wrapper，拿到接口中所有的方法名字
        String[] methods = Wrapper.getWrapper(interfaceClass).getMethodNames();
        if (methods.length == 0) {
            logger.warn("No method found in service interface " + interfaceClass.getName());
            map.put(METHODS_KEY, ANY_VALUE);
        } else {
            map.put(METHODS_KEY, StringUtils.join(new HashSet(Arrays.asList(methods)), ","));
        }
    }

    // Token是为了防止服务被消费者直接调用（伪造http请求）
    // 主要是存于注册中心，调用时Token匹配成功即算通过（所以要求调用者是通过注册中心获取提供方的信息）
    if (!ConfigUtils.isEmpty(token)) {
        if (ConfigUtils.isDefault(token)) {
            map.put(TOKEN_KEY, UUID.randomUUID().toString());
        } else {
            map.put(TOKEN_KEY, token);
        }
    }

    // export service
    // 通过该host和port访问该服务
    String host = this.findConfigedHosts(protocolConfig, registryURLs, map);
    Integer port = this.findConfigedPorts(protocolConfig, name, map);
    // 服务url
    URL url = new URL(name, host, port, getContextPath(protocolConfig).map(p -> p + "/" + path).orElse(path), map);
    // url：http://192.168.40.17:80/org.apache.dubbo.demo.DemoService?anyhost=true&application=dubbo-demo-annotation-provider&bean.name=ServiceBean:org.apache.dubbo.demo.DemoService&bind.ip=192.168.40.17&bind.port=80&deprecated=false&dubbo=2.0.2&dynamic=true&generic=false&interface=org.apache.dubbo.demo.DemoService&methods=sayHello&pid=285072&release=&side=provider×tamp=1585206500409

    // 可以通过ConfiguratorFactory，在服务导出时候进行统一配置
    if (ExtensionLoader.getExtensionLoader(ConfiguratorFactory.class).hasExtension(url.getProtocol())) {
        url = ExtensionLoader.getExtensionLoader(ConfiguratorFactory.class).getExtension(url.getProtocol()).getConfigurator(url).configure(url);
    }

    String scope = url.getParameter(SCOPE_KEY); // scope可能为null，remote, local,none
    // don't export when none is configured
    if (!SCOPE_NONE.equalsIgnoreCase(scope)) {
        // 如果scope为none,则不会进行任何的服务导出，既不会远程，也不会本地

        // export to local if the config is not remote (export to remote only when config is remote)
        if (!SCOPE_REMOTE.equalsIgnoreCase(scope)) {
            // 如果scope不是remote,则会进行本地导出，会把当前url的protocol改为injvm，然后进行导出
            exportLocal(url);
        }
        // export to remote if the config is not local (export to local only when config is local)
        if (!SCOPE_LOCAL.equalsIgnoreCase(scope)) {
            // 如果scope不是local,则会进行远程导出

            if (CollectionUtils.isNotEmpty(registryURLs)) {
                // 如果有注册中心，则将服务注册到注册中心
                for (URL registryURL : registryURLs) {

                    //if protocol is only injvm ,not register
                    // 如果是injvm，则不需要进行注册中心注册
                    if (LOCAL_PROTOCOL.equalsIgnoreCase(url.getProtocol())) {
                        continue;
                    }

                    // 该服务是否是动态，对应zookeeper上表示是否是临时节点，对应dubbo中的功能就是静态服务
                    url = url.addParameterIfAbsent(DYNAMIC_KEY, registryURL.getParameter(DYNAMIC_KEY));

                    // 基于注册中心地址的到监控中心地址，为什么是基于注册中心地址？
                    URL monitorUrl = loadMonitor(registryURL);

                    // 把监控中心地址添加到服务url中
                    if (monitorUrl != null) {
                        url = url.addParameterAndEncoded(MONITOR_KEY, monitorUrl.toFullString());
                    }

                    // 服务的register参数，如果为true，则表示要注册到注册中心
                    if (logger.isInfoEnabled()) {
                        if (url.getParameter(REGISTER_KEY, true)) {
                            logger.info(...);
                        } else {
                            logger.info(...);
                        }
                    }

                    // For providers, this is used to enable custom proxy to generate invoker
                    // 服务使用的动态代理机制，如果为空则使用javassit
                    String proxy = url.getParameter(PROXY_KEY);
                    if (StringUtils.isNotEmpty(proxy)) {
                        registryURL = registryURL.addParameter(PROXY_KEY, proxy);
                    }

                    // 生成一个当前服务接口的代理对象
                    // 使用代理生成一个Invoker，Invoker表示服务提供者的代理，可以使用Invoker的invoke方法执行服务
                    // 对应的url为 registry://127.0.0.1:2181/org.apache.dubbo.registry.RegistryService?application=dubbo-demo-annotation-provider&dubbo=2.0.2&export=http%3A%2F%2F192.168.40.17%3A80%2Forg.apache.dubbo.demo.DemoService%3Fanyhost%3Dtrue%26application%3Ddubbo-demo-annotation-provider%26bean.name%3DServiceBean%3Aorg.apache.dubbo.demo.DemoService%26bind.ip%3D192.168.40.17%26bind.port%3D80%26deprecated%3Dfalse%26dubbo%3D2.0.2%26dynamic%3Dtrue%26generic%3Dfalse%26interface%3Dorg.apache.dubbo.demo.DemoService%26methods%3DsayHello%26pid%3D19472%26release%3D%26side%3Dprovider%26timestamp%3D1585207994860&pid=19472®istry=zookeeper×tamp=1585207994828
                    // 这个Invoker中包括了服务的实现者、服务接口类、服务的注册地址（针对当前服务的，参数export指定了当前服务）
                    // 此invoker表示一个可执行的服务，调用invoker的invoke()方法即可执行服务,同时此invoker也可用来导出
                    Invoker invoker = PROXY_FACTORY.getInvoker(ref, (Class) interfaceClass, registryURL.addParameterAndEncoded(EXPORT_KEY, url.toFullString()));

                    // DelegateProviderMetaDataInvoker也表示服务提供者，包括了Invoker和服务的配置
                    DelegateProviderMetaDataInvoker wrapperInvoker = new DelegateProviderMetaDataInvoker(invoker, this);

                    // 使用特定的协议来对服务进行导出，这里的协议为RegistryProtocol，导出成功后得到一个Exporter
                    // 1. 先使用RegistryProtocol进行服务注册
                    // 2. 注册完了之后，使用DubboProtocol进行导出
                    Exporter exporter = protocol.export(wrapperInvoker);
                    exporters.add(exporter);
                }
            } else {
                // 没有配置注册中心时，也会导出服务

                Invoker invoker = PROXY_FACTORY.getInvoker(ref, (Class) interfaceClass, url);
                DelegateProviderMetaDataInvoker wrapperInvoker = new DelegateProviderMetaDataInvoker(invoker, this);

                Exporter exporter = protocol.export(wrapperInvoker);
                exporters.add(exporter);
            }


            // 根据服务url，讲服务的元信息存入元数据中心
            MetadataReportService metadataReportService = null;
            if ((metadataReportService = getMetadataReportService()) != null) {
                metadataReportService.publishProvider(url);
            }
        }
    }
    this.urls.add(url);
}

 

　　　　7）protocol.export的调用

@Override
public  Exporter export(final Invoker originInvoker) throws RpcException {
    // 导出服务
    // registry://   ---> RegistryProtocol
    // zookeeper://  ---> ZookeeperRegistry
    // dubbo://      ---> DubboProtocol
    // provider://   --->

    // 将registry://xxx?xx=xx®istry=zookeeper 转为---> zookeeper://xxx?xx=xx
    URL registryUrl = getRegistryUrl(originInvoker); // zookeeper://127.0.0.1:2181/org.apache.dubbo.registry.RegistryService?application=dubbo-demo-provider-application&dubbo=2.0.2&export=dubbo%3A%2F%2F192.168.40.17%3A20880%2Forg.apache.dubbo.demo.DemoService%3Fanyhost%3Dtrue%26application%3Ddubbo-demo-provider-application%26bean.name%3DServiceBean%3Aorg.apache.dubbo.demo.DemoService%26bind.ip%3D192.168.40.17%26bind.port%3D20880%26deprecated%3Dfalse%26dubbo%3D2.0.2%26dynamic%3Dtrue%26generic%3Dfalse%26interface%3Dorg.apache.dubbo.demo.DemoService%26logger%3Dlog4j%26methods%3DsayHello%26pid%3D27656%26release%3D2.7.0%26side%3Dprovider%26timeout%3D3000%26timestamp%3D1590735956489&logger=log4j&pid=27656&release=2.7.0×tamp=1590735956479
    // 得到服务提供者url
    URL providerUrl = getProviderUrl(originInvoker); // dubbo://192.168.40.17:20880/org.apache.dubbo.demo.DemoService?anyhost=true&application=dubbo-demo-provider-application&bean.name=ServiceBean:org.apache.dubbo.demo.DemoService&bind.ip=192.168.40.17&bind.port=20880&deprecated=false&dubbo=2.0.2&dynamic=true&generic=false&interface=org.apache.dubbo.demo.DemoService&logger=log4j&methods=sayHello&pid=27656&release=2.7.0&side=provider&timeout=3000×tamp=1590735956489

    // Subscribe the override data
    // FIXME When the provider subscribes, it will affect the scene : a certain JVM exposes the service and call
    //  the same service. Because the subscribed is cached key with the name of the service, it causes the
    //  subscription information to cover.

    // overrideSubscribeUrl是老版本的动态配置监听url，表示了需要监听的服务以及监听的类型（configurators， 这是老版本上的动态配置）
    // 在服务提供者url的基础上，生成一个overrideSubscribeUrl，协议为provider://，增加参数category=configurators&check=false
    final URL overrideSubscribeUrl = getSubscribedOverrideUrl(providerUrl);

    // 一个overrideSubscribeUrl对应一个OverrideListener，用来监听变化事件，监听到overrideSubscribeUrl的变化后，
    // OverrideListener就会根据变化进行相应处理，具体处理逻辑看OverrideListener的实现
    final OverrideListener overrideSubscribeListener = new OverrideListener(overrideSubscribeUrl, originInvoker);
    overrideListeners.put(overrideSubscribeUrl, overrideSubscribeListener);


    // 在这个方法里会利用providerConfigurationListener和serviceConfigurationListener去重写providerUrl
    // providerConfigurationListener表示应用级别的动态配置监听器，providerConfigurationListener是RegistyProtocol的一个属性
    // serviceConfigurationListener表示服务级别的动态配置监听器，serviceConfigurationListener是在每暴露一个服务时就会生成一个
    // 这两个监听器都是新版本中的监听器
    // 新版本监听的zk路径是：
    // 服务： /dubbo/config/dubbo/org.apache.dubbo.demo.DemoService.configurators节点的内容
    // 应用： /dubbo/config/dubbo/dubbo-demo-provider-application.configurators节点的内容
    // 注意，要喝配置中心的路径区分开来，配置中心的路径是：
    // 应用：/dubbo/config/dubbo/org.apache.dubbo.demo.DemoService/dubbo.properties节点的内容
    // 全局：/dubbo/config/dubbo/dubbo.properties节点的内容
    providerUrl = overrideUrlWithConfig(providerUrl, overrideSubscribeListener);

    // export invoker
    // 根据动态配置重写了providerUrl之后，就会调用DubboProtocol或HttpProtocol去进行导出服务了
    final ExporterChangeableWrapper exporter = doLocalExport(originInvoker, providerUrl);

    // url to registry
    // 得到注册中心-ZookeeperRegistry
    final Registry registry = getRegistry(originInvoker);

    // 得到存入到注册中心去的providerUrl,会对服务提供者url中的参数进行简化
    final URL registeredProviderUrl = getRegisteredProviderUrl(providerUrl, registryUrl);

    // 将当前服务提供者Invoker，以及该服务对应的注册中心地址，以及简化后的服务url存入ProviderConsumerRegTable
    ProviderInvokerWrapper providerInvokerWrapper = ProviderConsumerRegTable.registerProvider(originInvoker, registryUrl, registeredProviderUrl);


    //to judge if we need to delay publish
    //是否需要注册到注册中心
    boolean register = providerUrl.getParameter(REGISTER_KEY, true);
    if (register) {
        // 注册服务，把简化后的服务提供者url注册到registryUrl中去
        register(registryUrl, registeredProviderUrl);
        providerInvokerWrapper.setReg(true);
    }

    // 针对老版本的动态配置，需要把overrideSubscribeListener绑定到overrideSubscribeUrl上去进行监听
    // 兼容老版本的配置修改，利用overrideSubscribeListener去监听旧版本的动态配置变化
    // 监听overrideSubscribeUrl   provider://192.168.40.17:20880/org.apache.dubbo.demo.DemoService?anyhost=true&application=dubbo-demo-annotation-provider&bean.name=ServiceBean:org.apache.dubbo.demo.DemoService&bind.ip=192.168.40.17&bind.port=20880&category=configurators&check=false&deprecated=false&dubbo=2.0.2&dynamic=true&generic=false&interface=org.apache.dubbo.demo.DemoService&methods=sayHello&pid=416332&release=&side=provider×tamp=1585318241955
    // 那么新版本的providerConfigurationListener和serviceConfigurationListener是在什么时候进行订阅的呢？在这两个类构造的时候
    // Deprecated! Subscribe to override rules in 2.6.x or before.
    // 老版本监听的zk路径是：/dubbo/org.apache.dubbo.demo.DemoService/configurators/override://0.0.0.0/org.apache.dubbo.demo.DemoService?category=configurators&compatible_config=true&dynamic=false&enabled=true&timeout=6000
    // 监听的是路径的内容，不是节点的内容
    registry.subscribe(overrideSubscribeUrl, overrideSubscribeListener);


    exporter.setRegisterUrl(registeredProviderUrl);
    exporter.setSubscribeUrl(overrideSubscribeUrl);
    //Ensure that a new exporter instance is returned every time export
    return new DestroyableExporter<>(exporter);
}

public void register(URL registryUrl, URL registeredProviderUrl) {
    Registry registry = registryFactory.getRegistry(registryUrl);
    // 调用FailbackRegistry类的方法再转到ZookeeperRegistry的register方法
    registry.register(registeredProviderUrl);
}

//FailbackRegistry类（进行失败重试）
@Override
public void register(URL url) {
    super.register(url);
    removeFailedRegistered(url);
    removeFailedUnregistered(url);
    try {
        // 这里才会调用ZookeeperRegistry类的方法
        doRegister(url);
    } catch (Exception e) {
        Throwable t = e;

        // If the startup detection is opened, the Exception is thrown directly.
        boolean check = getUrl().getParameter(Constants.CHECK_KEY, true) && url.getParameter(Constants.CHECK_KEY, true) && !CONSUMER_PROTOCOL.equals(url.getProtocol());
        boolean skipFailback = t instanceof SkipFailbackWrapperException;
        if (check || skipFailback) {
            if (skipFailback) {
                t = t.getCause();
            }
            throw new IllegalStateException(...);
        } else {
            logger.error(...);
        }
        addFailedRegistered(url);
    }
}

//ZookeeperRegistry的真正注册的地方
@Override
public void doRegister(URL url) {
    try {
        zkClient.create(toUrlPath(url), url.getParameter(DYNAMIC_KEY, true));
    } catch (Throwable e) {
        throw new RpcException("Failed to register " + url + " to zookeeper " + getUrl() + ", cause: " + e.getMessage(), e);
    }
}

　　　　8）doLocalExport方法

@SuppressWarnings("unchecked")
private  ExporterChangeableWrapper doLocalExport(final Invoker originInvoker, URL providerUrl) {
    String key = getCacheKey(originInvoker);

    return (ExporterChangeableWrapper) bounds.computeIfAbsent(key, s -> {
        Invoker invokerDelegate = new InvokerDelegate<>(originInvoker, providerUrl);
        // protocol属性的值是哪来的，是在SPI中注入进来的，是一个代理类
        // 这里实际利用的就是DubboProtocol或HttpProtocol去export  NettyServer
        // 为什么需要ExporterChangeableWrapper？方便注销已经被导出的服务
        return new ExporterChangeableWrapper<>((Exporter) protocol.export(invokerDelegate), originInvoker);
    });
}

@Override
public  Exporter export(Invoker invoker) throws RpcException {
    URL url = invoker.getUrl();

    // export service.
    String key = serviceKey(url);
    // 构造一个Exporter
    DubboExporter exporter = new DubboExporter(invoker, key, exporterMap);
    exporterMap.put(key, exporter);

    //export an stub service for dispatching event
    Boolean isStubSupportEvent = url.getParameter(STUB_EVENT_KEY, DEFAULT_STUB_EVENT);
    Boolean isCallbackservice = url.getParameter(IS_CALLBACK_SERVICE, false);
    if (isStubSupportEvent && !isCallbackservice) {
        String stubServiceMethods = url.getParameter(STUB_EVENT_METHODS_KEY);
        if (stubServiceMethods == null || stubServiceMethods.length() == 0) {
            if (logger.isWarnEnabled()) {
                logger.warn(...);
            }
        } else {
            // 服务的stub方法
            stubServiceMethodsMap.put(url.getServiceKey(), stubServiceMethods);
        }
    }

    // 开启NettyServer
    openServer(url);

    optimizeSerialization(url);

    return exporter;
}

private void openServer(URL url) {
    // find server.
    String key = url.getAddress(); // 获得ip地址和port， 192.168.40.17:20880

    // NettyClient, NettyServer
    //client can export a service which's only for server to invoke
    boolean isServer = url.getParameter(IS_SERVER_KEY, true);
    if (isServer) {
        // 缓存Server对象
        ExchangeServer server = serverMap.get(key);

        // DCL，Double Check Lock
        if (server == null) {
            synchronized (this) {
                server = serverMap.get(key);
                if (server == null) {
                    // 创建Server，并进行缓存
                    serverMap.put(key, createServer(url));
                }
            }
        } else {
            // server supports reset, use together with override
            // 服务重新导出时，就会走这里
            server.reset(url);
        }
    }
}

private ExchangeServer createServer(URL url) {
    url = URLBuilder.from(url)
            // send readonly event when server closes, it's enabled by default
            .addParameterIfAbsent(CHANNEL_READONLYEVENT_SENT_KEY, Boolean.TRUE.toString())
            // enable heartbeat by default
            .addParameterIfAbsent(HEARTBEAT_KEY, String.valueOf(DEFAULT_HEARTBEAT))
            .addParameter(CODEC_KEY, DubboCodec.NAME)
            .build();

    // 协议的服务器端实现类型，比如：dubbo协议的mina,netty等，http协议的jetty,servlet等，默认为netty
    String str = url.getParameter(SERVER_KEY, DEFAULT_REMOTING_SERVER);

    if (str != null && str.length() > 0 && !ExtensionLoader.getExtensionLoader(Transporter.class).hasExtension(str)) {
        throw new RpcException("Unsupported server type: " + str + ", url: " + url);
    }

    // 通过url绑定端口，和对应的请求处理器
    ExchangeServer server;
    try {
        // requestHandler是请求处理器，类型为ExchangeHandler
        // 表示从url的端口接收到请求后，requestHandler来进行处理
        server = Exchangers.bind(url, requestHandler);
    } catch (RemotingException e) {
        throw new RpcException("Fail to start server(url: " + url + ") " + e.getMessage(), e);
    }

    // 协议的客户端实现类型，比如：dubbo协议的mina,netty等
    str = url.getParameter(CLIENT_KEY);
    if (str != null && str.length() > 0) {
        Set supportedTypes = ExtensionLoader.getExtensionLoader(Transporter.class).getSupportedExtensions();
        if (!supportedTypes.contains(str)) {
            throw new RpcException("Unsupported client type: " + str);
        }
    }

    return server;
}

　　　　9）当数据发生改变时 OverrideListener 监听者的处理

@Override
public synchronized void notify(List urls) {

    List matchedUrls = getMatchedUrls(urls, subscribeUrl.addParameter(CATEGORY_KEY, CONFIGURATORS_CATEGORY));
    // No matching results
    if (matchedUrls.isEmpty()) {
        return;
    }

    // 对发生了变化的url进行过滤，只取url是override协议，或者参数category等于configurators的url
    this.configurators = Configurator.toConfigurators(classifyUrls(matchedUrls, UrlUtils::isConfigurator)).orElse(configurators);
    // 根据Override协议修改
    doOverrideIfNecessary();
}

public synchronized void doOverrideIfNecessary() {
    final Invoker invoker;
    if (originInvoker instanceof InvokerDelegate) {
        invoker = ((InvokerDelegate) originInvoker).getInvoker();
    } else {
        invoker = originInvoker;
    }
    //The origin invoker 当前服务的原始服务提供者url
    URL originUrl = RegistryProtocol.this.getProviderUrl(invoker);
    String key = getCacheKey(originInvoker);

    ExporterChangeableWrapper exporter = bounds.get(key);
    if (exporter == null) {
        logger.warn(new IllegalStateException("error state, exporter should not be null"));
        return;
    }

    //The current, may have been merged many times，当前服务被导出的url
    URL currentUrl = exporter.getInvoker().getUrl();

    //根据configurators修改url，configurators是全量的，并不是某个新增的或删除的，所以是基于原始的url进行修改，并不是基于currentUrl
    //Merged with this configuration
    URL newUrl = getConfigedInvokerUrl(configurators, originUrl);

    newUrl = getConfigedInvokerUrl(providerConfigurationListener.getConfigurators(), newUrl);
    newUrl = getConfigedInvokerUrl(serviceConfigurationListeners.get(originUrl.getServiceKey()).getConfigurators(), newUrl);

    // 修改过的url如果和目前的url不相同，则重新按newUrl导出
    if (!currentUrl.equals(newUrl)) {
        RegistryProtocol.this.reExport(originInvoker, newUrl);
        logger.info(...);
    }
}

public  void reExport(final Invoker originInvoker, URL newInvokerUrl) {

    // 根据newInvokerUrl进行导出
    // update local exporter
    ExporterChangeableWrapper exporter = doChangeLocalExport(originInvoker, newInvokerUrl);

    // 获取准确的ProviderUrl
    // update registry
    URL registryUrl = getRegistryUrl(originInvoker);
    // 对于一个服务提供者url，在注册到注册中心时，会先进行简化，所以如果
    final URL registeredProviderUrl = getRegisteredProviderUrl(newInvokerUrl, registryUrl);

    //decide if we need to re-publish
    // 根据getServiceKey获取ProviderInvokerWrapper
    ProviderInvokerWrapper providerInvokerWrapper = ProviderConsumerRegTable.getProviderWrapper(registeredProviderUrl, originInvoker);
    // 生成一个新的ProviderInvokerWrapper
    ProviderInvokerWrapper newProviderInvokerWrapper = ProviderConsumerRegTable.registerProvider(originInvoker, registryUrl, registeredProviderUrl);

    /**
     * Only if the new url going to Registry is different with the previous one should we do unregister and register.
     * 如果新的服务提供者url简化后的url和这个服务之前的服务提供者url简化后的url不相等，则需要把新的简化后的服务提供者url注册到注册中心去
     */
    if (providerInvokerWrapper.isReg() && !registeredProviderUrl.equals(providerInvokerWrapper.getProviderUrl())) {
        unregister(registryUrl, providerInvokerWrapper.getProviderUrl());
        register(registryUrl, registeredProviderUrl);
        newProviderInvokerWrapper.setReg(true);
    }

    exporter.setRegisterUrl(registeredProviderUrl);
}

@SuppressWarnings("unchecked")
private  ExporterChangeableWrapper doChangeLocalExport(final Invoker originInvoker, URL newInvokerUrl) {
    String key = getCacheKey(originInvoker);
    final ExporterChangeableWrapper exporter = (ExporterChangeableWrapper) bounds.get(key);
    if (exporter == null) {
        logger.warn(new IllegalStateException("error state, exporter should not be null"));
    } else {
        // 到这里才能真正明白，为什么需要InvokerDelegate
        // InvokerDelegate表示一个调用者，由invoker+url构成，invoker不变，url可变
        final Invoker invokerDelegate = new InvokerDelegate(originInvoker, newInvokerUrl);
        //这次openServer会走HeaderExchangeServer的reset方法
        exporter.setExporter(protocol.export(invokerDelegate));
    }
    return exporter;
}

//这里面存在重新导出，关闭旧的延迟任务（旧的心跳任务），开启新的心跳任务，但是Netty不会关闭，也不会重启
@Override
public void reset(URL url) {
    server.reset(url);
    try {
        int currHeartbeat = getHeartbeat(getUrl());
        int currIdleTimeout = getIdleTimeout(getUrl());
        int heartbeat = getHeartbeat(url);
        int idleTimeout = getIdleTimeout(url);
        if (currHeartbeat != heartbeat || currIdleTimeout != idleTimeout) {
            cancelCloseTask();
            startIdleCheckTask(url);
        }
    } catch (Throwable t) {
        logger.error(t.getMessage(), t);
    }
}

 

　　【3】汇总

服务导出的入口为ServiceBean中的export()方法，当Spring启动完之后，通过接收Spring的ContextRefreshedEvent事件来触发export()方法的执行。

一个ServiceBean对象就表示一个Dubbo服务，ServiceBean对象中的参数就表示服务的参数，比如timeout，该对象的参数值来至@Service注解中所定义的。

服务导出主要得做两件事情：
1. 根据服务的参数信息，启动对应的网络服务器（netty、tomcat、jetty等），用来接收网络请求
2. 将服务的信息注册到注册中心

但是在做这两件事情之前得先把服务的参数确定好，因为一个Dubbo服务的参数，除开可以在@Service注解中去配置，还会继承Dubbo服务所属应用（Application）上的配置，
还可以在配置中心或JVM环境变量中去配置某个服务的参数，所以首先要做的是确定好当前服务最终的（优先级最高）的参数值。

确定好服务参数之后，就根据所配置的协议启动对应的网络服务器。在启动网络服务器时，并且在网络服务器接收请求的过程中，都可以从服务参数中获取信息，比如最大连接数，线程数，socket超时时间等等。

启动完网络服务器之后，就将服务信息注册到注册中心。同时还有向注册中心注册监听器，监听Dubbo的中的动态配置信息变更。

 

Dubbo服务引入

　　【0】核心点记录

生成代理对象（代理对象应该包含的功能）{
    1.获取服务提供者列表
    2.Mock--------MockClusterInvoker
    3.路由筛选
    4.负载均衡
    5.集群容错------FailoverClusterInvoker
    6.构造NettyClient
    7.发送数据（Invocation）
}

代理对象的Invoker
MockClusterInvoker
    Invoker属性塞入FailoverClusterInvoker
        FailoverClusterInvoker
            Invoker属性塞入DubboInvoker

 

　　【1】服务要怎么引入（ReferenceConfig类#get()方法）

//服务引入的入口方法
public synchronized T get() {
    //读取配置并补全（最新最全的配置）
    checkAndUpdateSubConfigs();
    if (destroyed) {
        throw new IllegalStateException(...);
    }
    if (ref == null) {
        // 入口
        init();
    }
    return ref;  // Invoke代理
}

 

　　【2】检查并拿到最新配置（ReferenceConfig类#checkAndUpdateSubConfigs()方法）

public void checkAndUpdateSubConfigs() {
  if (StringUtils.isEmpty(interfaceName)) {
      throw new IllegalStateException(...);
  }
  // 填充ReferenceConfig对象中的属性
  completeCompoundConfigs();
  // 开启配置中心
  startConfigCenter();
  // get consumer's global configuration
  checkDefault();
  // 刷新ReferenceConfig对象的属性值
  this.refresh();

  // 设置泛化
  if (getGeneric() == null && getConsumer() != null) {
      setGeneric(getConsumer().getGeneric());
  }

  if (ProtocolUtils.isGeneric(getGeneric())) {
      interfaceClass = GenericService.class;
  } else {
      try {
          interfaceClass = Class.forName(interfaceName, true, Thread.currentThread().getContextClassLoader());
      } catch (ClassNotFoundException e) {
          throw new IllegalStateException(...);
      }
      checkInterfaceAndMethods(interfaceClass, methods);
  }


  resolveFile();
  checkApplication();
  checkMetadataReport();
}

 

　　【3】初始化生成代理对象（ReferenceConfig类#init()方法）

private void init() {
    if (initialized) {
        return;
    }

    //准备参数，进行参数配置
    checkStubAndLocal(interfaceClass);
    checkMock(interfaceClass);
    Map map = new HashMap();

    map.put(SIDE_KEY, CONSUMER_SIDE);

    appendRuntimeParameters(map);
    if (!ProtocolUtils.isGeneric(getGeneric())) {
        String revision = Version.getVersion(interfaceClass, version);
        if (revision != null && revision.length() > 0) {
            map.put(REVISION_KEY, revision);
        }

        String[] methods = Wrapper.getWrapper(interfaceClass).getMethodNames();
        if (methods.length == 0) {
            logger.warn("No method found in service interface " + interfaceClass.getName());
            map.put(METHODS_KEY, ANY_VALUE);
        } else {
            map.put(METHODS_KEY, StringUtils.join(new HashSet(Arrays.asList(methods)), COMMA_SEPARATOR));
        }
    }
    map.put(INTERFACE_KEY, interfaceName);
    appendParameters(map, metrics);
    appendParameters(map, application);
    appendParameters(map, module);
    // remove 'default.' prefix for configs from ConsumerConfig
    // appendParameters(map, consumer, Constants.DEFAULT_KEY);
    appendParameters(map, consumer);
    appendParameters(map, this);

    Map attributes = null;
    if (CollectionUtils.isNotEmpty(methods)) {
        attributes = new HashMap();
        for (MethodConfig methodConfig : methods) {
            appendParameters(map, methodConfig, methodConfig.getName());
            String retryKey = methodConfig.getName() + ".retry";
            if (map.containsKey(retryKey)) {
                String retryValue = map.remove(retryKey);
                if ("false".equals(retryValue)) {
                    map.put(methodConfig.getName() + ".retries", "0");
                }
            }

            attributes.put(methodConfig.getName(), convertMethodConfig2AsyncInfo(methodConfig));
        }
    }

    String hostToRegistry = ConfigUtils.getSystemProperty(DUBBO_IP_TO_REGISTRY);
    if (StringUtils.isEmpty(hostToRegistry)) {
        hostToRegistry = NetUtils.getLocalHost();
    } else if (isInvalidLocalHost(hostToRegistry)) {
        throw new IllegalArgumentException(...);
    }
    map.put(REGISTER_IP_KEY, hostToRegistry);
    
    //参数配置完成后去生成代理对象
    ref = createProxy(map);

    String serviceKey = URL.buildKey(interfaceName, group, version);
    ApplicationModel.initConsumerModel(serviceKey, buildConsumerModel(serviceKey, attributes));
    initialized = true;
}

 

　　【4】生成代理对象（ReferenceConfig类#createProxy()方法）

@SuppressWarnings({"unchecked", "rawtypes", "deprecation"})
private T createProxy(Map map) {
    if (shouldJvmRefer(map)) {
        // injvm://
        URL url = new URL(LOCAL_PROTOCOL, LOCALHOST_VALUE, 0, interfaceClass.getName()).addParameters(map);
        invoker = REF_PROTOCOL.refer(interfaceClass, url);
    } else {
        // 为什么会有urls，因为可以在@Reference的url属性中配置多个url，可以是点对点的服务地址，也可以是注册中心的地址
        urls.clear(); // reference retry init will add url to urls, lead to OOM
        // @Reference中指定了url属性
        if (url != null && url.length() > 0) { // user specified URL, could be peer-to-peer address, or register center's address.
            String[] us = SEMICOLON_SPLIT_PATTERN.split(url); // 用;号切分
            if (us != null && us.length > 0) {
                for (String u : us) {
                    URL url = URL.valueOf(u);
                    if (StringUtils.isEmpty(url.getPath())) {
                        url = url.setPath(interfaceName);
                    }

                    // 如果是注册中心地址，则在url中添加一个refer参数
                    if (REGISTRY_PROTOCOL.equals(url.getProtocol())) {
                        // map表示消费者端配置的参数
                        urls.add(url.addParameterAndEncoded(REFER_KEY, StringUtils.toQueryString(map)));
                    } else {
                        // 如果是服务地址
                        // 有可能url中配置了参数，map中表示的服务消费者消费服务时的参数，所以需要合并
                        urls.add(ClusterUtils.mergeUrl(url, map));
                    }
                }
            }
        } else { // assemble URL from register center's configuration
            // @Reference中的protocol属性表示使用哪个协议调用服务，如果不是本地调用协议injvm://，则把注册中心地址找出来
            // 对于injvm://协议已经在之前的逻辑中就已经生成invoke了
            // if protocols not injvm checkRegistry
            if (!LOCAL_PROTOCOL.equalsIgnoreCase(getProtocol())){
                checkRegistry();
                // 加载注册中心地址
                List us = loadRegistries(false);
                if (CollectionUtils.isNotEmpty(us)) {
                    for (URL u : us) {
                        URL monitorUrl = loadMonitor(u);
                        if (monitorUrl != null) {
                            map.put(MONITOR_KEY, URL.encode(monitorUrl.toFullString()));
                        }
                        // 对于注册中心地址都添加REFER_KEY
                        urls.add(u.addParameterAndEncoded(REFER_KEY, StringUtils.toQueryString(map)));
                    }
                }
                if (urls.isEmpty()) {
                    throw new IllegalStateException(...);
                }
            }
        }

        // 如果只有一个url则直接refer得到一个invoker
        if (urls.size() == 1) {
            // RegistryProtocol.refer() 或者 DubboProtocol.refer()
            invoker = REF_PROTOCOL.refer(interfaceClass, urls.get(0));
        } else {
            // 如果有多个url
            // 1. 根据每个url，refer得到对应的invoker
            // 2. 如果这多个urls中存在注册中心url，则把所有invoker整合为RegistryAwareClusterInvoker，该Invoker在调用时，会查看所有Invoker中是否有默认的，如果有则使用默认的Invoker，如果没有，则使用第一个Invoker
            // 2. 如果这多个urls中不存在注册中心url，则把所有invoker整合为FailoverCluster

            List> invokers = new ArrayList>();
            URL registryURL = null; // 用来记录urls中最后一个注册中心url
            for (URL url : urls) {
                invokers.add(REF_PROTOCOL.refer(interfaceClass, url));

                if (REGISTRY_PROTOCOL.equals(url.getProtocol())) {
                    registryURL = url; // use last registry url
                }
            }

            // 如果存在注册中心地址
            if (registryURL != null) { // registry url is available
                // use RegistryAwareCluster only when register's CLUSTER is available
                URL u = registryURL.addParameter(CLUSTER_KEY, RegistryAwareCluster.NAME);
                // StaticDirectory表示静态服务目录，里面的invokers是不会变的, 生成一个RegistryAwareCluster
                // The invoker wrap relation would be: RegistryAwareClusterInvoker(StaticDirectory) -> FailoverClusterInvoker(RegistryDirectory, will execute route) -> Invoker
                invoker = CLUSTER.join(new StaticDirectory(u, invokers));
            } else { // not a registry url, must be direct invoke.
                // 如果不存在注册中心地址, 生成一个FailoverClusterInvoker
                invoker = CLUSTER.join(new StaticDirectory(invokers));
            }
        }
    }

    if (shouldCheck() && !invoker.isAvailable()) {
        throw new IllegalStateException(...);
    }
 
    MetadataReportService metadataReportService = null;
    if ((metadataReportService = getMetadataReportService()) != null) {
        URL consumerURL = new URL(CONSUMER_PROTOCOL, map.remove(REGISTER_IP_KEY), 0, map.get(INTERFACE_KEY), map);
        metadataReportService.publishConsumer(consumerURL);
    }
    // create service proxy
    return (T) PROXY_FACTORY.getProxy(invoker);
}

 

　　【5】PROXY_FACTORY.getProxy等过程

//默认采用JavassistProxyFactory来产生代理对象
public class JavassistProxyFactory extends AbstractProxyFactory {

    @Override
    @SuppressWarnings("unchecked")
    public  T getProxy(Invoker invoker, Class[] interfaces) {
        return (T) Proxy.getProxy(interfaces).newInstance(new InvokerInvocationHandler(invoker));
    }

    @Override
    public  Invoker getInvoker(T proxy, Class type, URL url) {

        // TODO Wrapper cannot handle this scenario correctly: the classname contains '$'
        // 如果现在被代理的对象proxy本身就是一个已经被代理过的对象，那么则取代理类的Wrapper，否则取type（接口）的Wrapper
        // Wrapper是针对某个类或某个接口的包装类，通过wrapper对象可以更方便的去执行某个类或某个接口的方法
        final Wrapper wrapper = Wrapper.getWrapper(proxy.getClass().getName().indexOf('$') < 0 ? proxy.getClass() : type);

        // proxy是服务实现类
        // type是服务接口
        // url是一个注册中心url，但同时也记录了
        return new AbstractProxyInvoker(proxy, type, url) {
            @Override
            protected Object doInvoke(T proxy, String methodName, Class[] parameterTypes, Object[] arguments) throws Throwable {

                // 执行proxy的method方法
                // 执行的proxy实例的方法
                // 如果没有wrapper，则要通过原生的反射技术去获取Method对象，然后执行
                return wrapper.invokeMethod(proxy, methodName, parameterTypes, arguments);
            }
        };
    }

}

public class InvokerInvocationHandler implements InvocationHandler {
    private static final Logger logger = LoggerFactory.getLogger(InvokerInvocationHandler.class);
    private final Invoker invoker;

    public InvokerInvocationHandler(Invoker handler) {
        this.invoker = handler;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        String methodName = method.getName();
        Class[] parameterTypes = method.getParameterTypes();
        if (method.getDeclaringClass() == Object.class) {
            return method.invoke(invoker, args);
        }
        if ("toString".equals(methodName) && parameterTypes.length == 0) {
            return invoker.toString();
        }
        if ("hashCode".equals(methodName) && parameterTypes.length == 0) {
            return invoker.hashCode();
        }
        if ("equals".equals(methodName) && parameterTypes.length == 1) {
            return invoker.equals(args[0]);
        }

        // 这里的recreate方法很重要，他会调用AppResponse的recreate方法，
        // 如果AppResponse对象中存在exception信息，则此方法中会throw这个异常
        return invoker.invoke(new RpcInvocation(method, args)).recreate();
    }
}

 

 

　　【6】对URL的处理过程

　　　　1）从@Reference的url属性中配置多个url，然后采用字符串分割的形式拿出来，包装后塞入urls列表中

　　　　2）加载注册中心地址

protected List loadRegistries(boolean provider) {
    // check && override if necessary
    List registryList = new ArrayList();
    if (CollectionUtils.isNotEmpty(registries)) {
        for (RegistryConfig config : registries) {
            String address = config.getAddress();
            // 如果注册中心没有配地址，则地址为0.0.0.0
            if (StringUtils.isEmpty(address)) {
                address = ANYHOST_VALUE;
            }
            // 如果注册中心的地址不是"N/A"
            if (!RegistryConfig.NO_AVAILABLE.equalsIgnoreCase(address)) {
                Map map = new HashMap();
                // 把application中的参数放入map中，注意，map中的key是没有prefix的
                appendParameters(map, application);
                // 把config中的参数放入map中，注意，map中的key是没有prefix的
                // config是RegistryConfig，表示注册中心
                appendParameters(map, config);
                // 此处path值固定为RegistryService.class.getName()，因为现在是在加载注册中心
                map.put(PATH_KEY, RegistryService.class.getName());
                // 把dubbo的版本信息和pid放入map中
                appendRuntimeParameters(map);

                // 如果map中如果没有protocol，那么默认为dubbo
                if (!map.containsKey(PROTOCOL_KEY)) {
                    map.put(PROTOCOL_KEY, DUBBO_PROTOCOL);
                }

                // 构造注册中心url，地址+参数
                List urls = UrlUtils.parseURLs(address, map);

                for (URL url : urls) {
                    url = URLBuilder.from(url)
                            .addParameter(REGISTRY_KEY, url.getProtocol())
                            .setProtocol(REGISTRY_PROTOCOL)
                            .build();
                    // 到此为止，url的内容大概为：
                    // registry://127.0.0.1:2181/org.apache.dubbo.registry.RegistryService?application=dubbo-demo-annotation-provider&dubbo=2.0.2&pid=269936®istry=zookeeper×tamp=1584886077813
                    // 该url表示：使用registry协议调用org.apache.dubbo.registry.RegistryService服务
                    // 参数为application=dubbo-demo-annotation-provider&dubbo=2.0.2&pid=269936®istry=zookeeper×tamp=1584886077813

                    // 这里是服务提供者和服务消费者区别的逻辑
                    // 如果是服务提供者，获取register的值，如果为false，表示该服务不注册到注册中心
                    // 如果是服务消费者，获取subscribe的值，如果为false，表示该引入的服务不订阅注册中心中的数据
                    if ((provider && url.getParameter(REGISTER_KEY, true))
                            || (!provider && url.getParameter(SUBSCRIBE_KEY, true))) {
                        registryList.add(url);
                    }
                }
            }
        }
    }
    return registryList;
}

 

　　【7】invoker的包装过程

　　　　1）前置说明

//RegistryProtocol实际上会被两个包装类包装ProtocolListenerWrapper与ProtocolFilterWrapper
//如ProtocolListenerWrapper的protocol属性存放ProtocolFilterWrapper
//ProtocolFilterWrapper的protocol属性存放RegistryProtocol

//然后是Cluster，通过接口可知默认是FailoverCluster，但实际上还会有一个包装类MockClusterWrapper
//MockClusterWrapper的cluster属性存放FailoverCluster或者RegistryAwareCluster

 

　　　　2）先是调用REF_PROTOCOL.refer

//ProtocolListenerWrapper的处理
@Override
public  Invoker refer(Class type, URL url) throws RpcException {
    if (REGISTRY_PROTOCOL.equals(url.getProtocol())) {
        return protocol.refer(type, url);
    }
    return new ListenerInvokerWrapper(protocol.refer(type, url),
            Collections.unmodifiableList(
                    ExtensionLoader.getExtensionLoader(InvokerListener.class)
                            .getActivateExtension(url, INVOKER_LISTENER_KEY)));
}
//ProtocolFilterWrapper的处理
@Override
public  Invoker refer(Class type, URL url) throws RpcException {
    if (REGISTRY_PROTOCOL.equals(url.getProtocol())) {
        return protocol.refer(type, url);
    }
    return buildInvokerChain(protocol.refer(type, url), REFERENCE_FILTER_KEY, CommonConstants.CONSUMER);
}
private static  Invoker buildInvokerChain(final Invoker invoker, String key, String group) {
    Invoker last = invoker;
    // 根据url获取filter，根据url中的parameters取key为key的value所对应的filter，但是还会匹配group
    List filters = ExtensionLoader.getExtensionLoader(Filter.class).getActivateExtension(invoker.getUrl(), key, group);

    // ConsumerContextFilter--->FutureFilter--->MonitorFilter
    // ConsumerContextFilter用来设置RpcContext
    if (!filters.isEmpty()) {
        for (int i = filters.size() - 1; i >= 0; i--) {
            final Filter filter = filters.get(i);
            final Invoker next = last;
            last = new Invoker() {

                @Override
                public Class getInterface() {
                    return invoker.getInterface();
                }

                @Override
                public URL getUrl() {
                    return invoker.getUrl();
                }

                @Override
                public boolean isAvailable() {
                    return invoker.isAvailable();
                }

                @Override
                public Result invoke(Invocation invocation) throws RpcException {
                    Result asyncResult;
                    try {
                        // 得到一个异步结果
                        asyncResult = filter.invoke(next, invocation);
                    } catch (Exception e) {
                        // onError callback
                        if (filter instanceof ListenableFilter) {
                            Filter.Listener listener = ((ListenableFilter) filter).listener();
                            if (listener != null) {
                                listener.onError(e, invoker, invocation);
                            }
                        }
                        throw e;
                    }
                    return asyncResult;
                }

                @Override
                public void destroy() {
                    invoker.destroy();
                }

                @Override
                public String toString() {
                    return invoker.toString();
                }
            };
        }
    }

    return new CallbackRegistrationInvoker<>(last, filters);
}

//RegistryProtocol的处理
public  Invoker refer(Class type, URL url) throws RpcException {

    // 从registry://的url中获取对应的注册中心，比如zookeeper， 默认为dubbo，dubbo提供了自带的注册中心实现
    // url由 registry:// 改变为---> zookeeper://
    url = URLBuilder.from(url)
            .setProtocol(url.getParameter(REGISTRY_KEY, DEFAULT_REGISTRY))
            .removeParameter(REGISTRY_KEY)
            .build();

    // 拿到注册中心实现，ZookeeperRegistry
    Registry registry = registryFactory.getRegistry(url);

    // 下面这个代码，通过过git历史提交记录是用来解决SimpleRegistry不可用的问题
    if (RegistryService.class.equals(type)) {
        return proxyFactory.getInvoker((T) registry, type, url);
    }

    // qs表示 queryString, 表示url中的参数，表示消费者引入服务时所配置的参数
    Map qs = StringUtils.parseQueryString(url.getParameterAndDecoded(REFER_KEY));

    // group="a,b" or group="*"
    String group = qs.get(GROUP_KEY);
    if (group != null && group.length() > 0) {
        if ((COMMA_SPLIT_PATTERN.split(group)).length > 1 || "*".equals(group)) {
            // group有多个值，这里的cluster为MergeableCluster
            return doRefer(getMergeableCluster(), registry, type, url);
        }
    }

    // 这里的cluster是cluster的Adaptive对象
    return doRefer(cluster, registry, type, url);
}

private  Invoker doRefer(Cluster cluster, Registry registry, Class type, URL url) {
    // RegistryDirectory表示动态服务目录，会和注册中心的数据保持同步
    // type表示一个服务对应一个RegistryDirectory，url表示注册中心地址
    // 在消费端，最核心的就是RegistryDirectory
    RegistryDirectory directory = new RegistryDirectory(type, url);
    directory.setRegistry(registry);
    directory.setProtocol(protocol);


    // all attributes of REFER_KEY
    // 引入服务所配置的参数
    Map parameters = new HashMap(directory.getUrl().getParameters());

    // 消费者url
    URL subscribeUrl = new URL(CONSUMER_PROTOCOL, parameters.remove(REGISTER_IP_KEY), 0, type.getName(), parameters);
    if (!ANY_VALUE.equals(url.getServiceInterface()) && url.getParameter(REGISTER_KEY, true)) {
        directory.setRegisteredConsumerUrl(getRegisteredConsumerUrl(subscribeUrl, url));

        // 注册简化后的消费url
        registry.register(directory.getRegisteredConsumerUrl());
    }

    // 构造路由链,路由链会在引入服务时按路由条件进行过滤
    // 路由链是动态服务目录中的一个属性，通过路由链可以过滤某些服务提供者
    directory.buildRouterChain(subscribeUrl);

    // 服务目录需要订阅的几个路径
    // 当前所引入的服务的消费应用目录：/dubbo/config/dubbo/dubbo-demo-consumer-application.configurators
    // 当前所引入的服务的动态配置目录：/dubbo/config/dubbo/org.apache.dubbo.demo.DemoService:1.1.1:g1.configurators
    // 当前所引入的服务的提供者目录：/dubbo/org.apache.dubbo.demo.DemoService/providers
    // 当前所引入的服务的老版本动态配置目录：/dubbo/org.apache.dubbo.demo.DemoService/configurators
    // 当前所引入的服务的老版本路由器目录：/dubbo/org.apache.dubbo.demo.DemoService/routers
    directory.subscribe(subscribeUrl.addParameter(CATEGORY_KEY,
            PROVIDERS_CATEGORY + "," + CONFIGURATORS_CATEGORY + "," + ROUTERS_CATEGORY));

    // 利用传进来的cluster，join得到invoker,
    Invoker invoker = cluster.join(directory);
    ProviderConsumerRegTable.registerConsumer(invoker, url, subscribeUrl, directory);
    return invoker;
}

 

　　　　3）再是调用CLUSTER.join

//MockClusterWrapper的处理
public class MockClusterWrapper implements Cluster {
    private Cluster cluster;
    public MockClusterWrapper(Cluster cluster) {
        this.cluster = cluster;
    }

    @Override
    public  Invoker join(Directory directory) throws RpcException {
        return new MockClusterInvoker(directory,
                this.cluster.join(directory));
    }
}

//有注册中心，RegistryAwareCluster的处理
public class RegistryAwareCluster implements Cluster {
    public final static String NAME = "registryaware";

    @Override
    public  Invoker join(Directory directory) throws RpcException {
        return new RegistryAwareClusterInvoker(directory);
    }
}

//没有注册中心，FailoverCluster的处理
public class FailoverCluster implements Cluster {
    public final static String NAME = "failover";
    @Override
    public  Invoker join(Directory directory) throws RpcException {
        return new FailoverClusterInvoker(directory);
    }
}

 

　　【8】RegistryProtocol里面的监听过程

 //directory.subscribe(subscribeUrl.addParameter(CATEGORY_KEY, PROVIDERS_CATEGORY + "," + CONFIGURATORS_CATEGORY + "," + ROUTERS_CATEGORY));

//RegistryDirectory类#subscribe方法
public void subscribe(URL url) {
    setConsumerUrl(url);
    CONSUMER_CONFIGURATION_LISTENER.addNotifyListener(this); // 监听consumer应用
    serviceConfigurationListener = new ReferenceConfigurationListener(this, url); // 监听所引入的服务的动态配置
    registry.subscribe(url, this); //老版本的监听
}

//FailbackRegistry类#subscribe方法
@Override
public void subscribe(URL url, NotifyListener listener) {
    super.subscribe(url, listener);
    removeFailedSubscribed(url, listener);
    try {
        // 核心方法
        doSubscribe(url, listener);
    } catch (Exception e) {
        Throwable t = e;

        List urls = getCacheUrls(url);
        if (CollectionUtils.isNotEmpty(urls)) {
            notify(url, listener, urls);
            logger.error(...);
        } else {
            // If the startup detection is opened, the Exception is thrown directly.
            boolean check = getUrl().getParameter(Constants.CHECK_KEY, true) && url.getParameter(Constants.CHECK_KEY, true);
            boolean skipFailback = t instanceof SkipFailbackWrapperException;
            if (check || skipFailback) {
                if (skipFailback) {
                    t = t.getCause();
                }
                throw new IllegalStateException("Failed to subscribe " + url + ", cause: " + t.getMessage(), t);
            } else {
                logger.error("Failed to subscribe " + url + ", waiting for retry, cause: " + t.getMessage(), t);
            }
        }

        // Record a failed registration request to a failed list, retry regularly
        // 添加listener，向zk添加监听器时如果报错了，那么会把这个listener添加到failedSubscribed中，并会定时重试（重新注册listener）
        addFailedSubscribed(url, listener);
    }
}

// 父类AbstractRegistry#subscribe方法
// 把listener添加到subscribed中，subscribed是一个map, 存的是URL:Set
@Override
public void subscribe(URL url, NotifyListener listener) {
    if (url == null) {
        throw new IllegalArgumentException("subscribe url == null");
    }
    if (listener == null) {
        throw new IllegalArgumentException("subscribe listener == null");
    }
    if (logger.isInfoEnabled()) {
        logger.info("Subscribe: " + url);
    }
    Set listeners = subscribed.computeIfAbsent(url, n -> new ConcurrentHashSet<>());
    listeners.add(listener);
}

// 进行订阅，先看父类的subscribe方法
@Override
public void doSubscribe(final URL url, final NotifyListener listener) {
    try {
        if (ANY_VALUE.equals(url.getServiceInterface())) {
            // 订阅所有服务

            String root = toRootPath();
            ConcurrentMap listeners = zkListeners.get(url);
            if (listeners == null) {
                zkListeners.putIfAbsent(url, new ConcurrentHashMap<>());
                listeners = zkListeners.get(url);
            }
            ChildListener zkListener = listeners.get(listener);
            if (zkListener == null) {
                listeners.putIfAbsent(listener, (parentPath, currentChilds) -> {
                    for (String child : currentChilds) {
                        child = URL.decode(child);
                        if (!anyServices.contains(child)) {
                            anyServices.add(child);
                            subscribe(url.setPath(child).addParameters(INTERFACE_KEY, child,
                                    Constants.CHECK_KEY, String.valueOf(false)), listener);
                        }
                    }
                });
                zkListener = listeners.get(listener);
            }
            zkClient.create(root, false);
            List services = zkClient.addChildListener(root, zkListener);
            if (CollectionUtils.isNotEmpty(services)) {
                for (String service : services) {
                    service = URL.decode(service);
                    anyServices.add(service);
                    subscribe(url.setPath(service).addParameters(INTERFACE_KEY, service,
                            Constants.CHECK_KEY, String.valueOf(false)), listener);
                }
            }
        } else {
            // 单独订阅某一个服务

            List urls = new ArrayList<>();
            // 得到真正要监听的zk上的路径,
            for (String path : toCategoriesPath(url)) {
                // 根据监听地址去拿listeners，如果没有则生成
                ConcurrentMap listeners = zkListeners.get(url);
                if (listeners == null) {
                    zkListeners.putIfAbsent(url, new ConcurrentHashMap<>());
                    listeners = zkListeners.get(url);
                }

                // 一个NotifyListener对应一个ChildListener
                ChildListener zkListener = listeners.get(listener);
                if (zkListener == null) {
                    // lambda表达式就是监听逻辑， parentPath表示父path,currentChilds表示当前拥有的child, 会调用notify方法进行实际的处理
                    listeners.putIfAbsent(listener, (parentPath, currentChilds) -> ZookeeperRegistry.this.notify(url, listener, toUrlsWithEmpty(url, parentPath, currentChilds)));
                    zkListener = listeners.get(listener);
                }
                // 创建zk上路径
                zkClient.create(path, false);

                // 添加真正跟zk相关的ChildListener,ChildListener中的逻辑就是监听到zk上数据发生了变化后会触发的逻辑
                List children = zkClient.addChildListener(path, zkListener);
                if (children != null) {
                    urls.addAll(toUrlsWithEmpty(url, path, children));
                }
            }
            // 这里的urls就是从现在所引入的服务的目录下查到的url，比如下面这个三个目录下的路径
//                "/dubbo/org.apache.dubbo.demo.DemoService/providers"
//                "/dubbo/org.apache.dubbo.demo.DemoService/configurators"
//                "/dubbo/org.apache.dubbo.demo.DemoService/routers"
            notify(url, listener, urls);
        }
    } catch (Throwable e) {
        throw new RpcException("Failed to subscribe " + url + " to zookeeper " + getUrl() + ", cause: " + e.getMessage(), e);
    }
}

 

　　【9】监听器触发时

//RegistryDirectory类#notify方法
public synchronized void notify(List urls) {
    Map> categoryUrls = urls.stream()
            .filter(Objects::nonNull)
            .filter(this::isValidCategory)
            .filter(this::isNotCompatibleFor26x)
            .collect(Collectors.groupingBy(url -> {
                if (UrlUtils.isConfigurator(url)) {
                    return CONFIGURATORS_CATEGORY;
                } else if (UrlUtils.isRoute(url)) {
                    return ROUTERS_CATEGORY;
                } else if (UrlUtils.isProvider(url)) {
                    return PROVIDERS_CATEGORY;
                }
                return "";
            }));

    // 获取动态配置URL，生成configurators
    List configuratorURLs = categoryUrls.getOrDefault(CONFIGURATORS_CATEGORY, Collections.emptyList());
    this.configurators = Configurator.toConfigurators(configuratorURLs).orElse(this.configurators);

    // 获取老版本路由URL，生成Router，并添加到路由链中
    List routerURLs = categoryUrls.getOrDefault(ROUTERS_CATEGORY, Collections.emptyList());
    toRouters(routerURLs).ifPresent(this::addRouters);

    // 获取服务提供者URL
    List providerURLs = categoryUrls.getOrDefault(PROVIDERS_CATEGORY, Collections.emptyList());
    refreshOverrideAndInvoker(providerURLs);
}

private void refreshOverrideAndInvoker(List urls) {
    // mock zookeeper://xxx?mock=return null
    overrideDirectoryUrl();
    refreshInvoker(urls);
}

// 利用动态配置重写服务目录地址
private void overrideDirectoryUrl() {
    // merge override parameters
    this.overrideDirectoryUrl = directoryUrl;
    List localConfigurators = this.configurators; // local reference
    doOverrideUrl(localConfigurators);

    List localAppDynamicConfigurators = CONSUMER_CONFIGURATION_LISTENER.getConfigurators(); // local reference
    doOverrideUrl(localAppDynamicConfigurators);

    if (serviceConfigurationListener != null) {
        List localDynamicConfigurators = serviceConfigurationListener.getConfigurators(); // local reference
        doOverrideUrl(localDynamicConfigurators);
    }
}

private void refreshInvoker(List invokerUrls) {
    Assert.notNull(invokerUrls, "invokerUrls should not be null");

    if (invokerUrls.size() == 1 && invokerUrls.get(0) != null && EMPTY_PROTOCOL.equals(invokerUrls.get(0).getProtocol())) {
        this.forbidden = true; // Forbid to access
        this.invokers = Collections.emptyList();
        routerChain.setInvokers(this.invokers);
        destroyAllInvokers(); // Close all invokers
    } else {
        this.forbidden = false; // Allow to access
        Map> oldUrlInvokerMap = this.urlInvokerMap; // local reference
        if (invokerUrls == Collections.emptyList()) {
            invokerUrls = new ArrayList<>();
        }
        if (invokerUrls.isEmpty() && this.cachedInvokerUrls != null) {
            invokerUrls.addAll(this.cachedInvokerUrls);
        } else {
            this.cachedInvokerUrls = new HashSet<>();
            this.cachedInvokerUrls.addAll(invokerUrls);//Cached invoker urls, convenient for comparison
        }
        if (invokerUrls.isEmpty()) {
            return;
        }
        // 这里会先按Protocol进行过滤，并且调用DubboProtocol.refer方法得到DubboInvoker
        Map> newUrlInvokerMap = toInvokers(invokerUrls);// Translate url list to Invoker map

        /**
         * If the calculation is wrong, it is not processed.
         *
         * 1. The protocol configured by the client is inconsistent with the protocol of the server.
         *    eg: consumer protocol = dubbo, provider only has other protocol services(rest).
         * 2. The registration center is not robust and pushes illegal specification data.
         *
         */
        if (CollectionUtils.isEmptyMap(newUrlInvokerMap)) {
            logger.error(...);
            return;
        }

        List> newInvokers = Collections.unmodifiableList(new ArrayList<>(newUrlInvokerMap.values()));
        // pre-route and build cache, notice that route cache should build on original Invoker list.
        // toMergeMethodInvokerMap() will wrap some invokers having different groups, those wrapped invokers not should be routed.
        // 得到了所引入的服务Invoker之后，把它们设置到路由链中去，在调用时使用，并且会调用TagRouter的notify方法
        routerChain.setInvokers(newInvokers);
        this.invokers = multiGroup ? toMergeInvokerList(newInvokers) : newInvokers;
        this.urlInvokerMap = newUrlInvokerMap;

        try {
            destroyUnusedInvokers(oldUrlInvokerMap, newUrlInvokerMap); // Close the unused Invoker
        } catch (Exception e) {
            logger.warn("destroyUnusedInvokers error. ", e);
        }
    }
}

private Map> toInvokers(List urls) {
    Map> newUrlInvokerMap = new HashMap<>();
    if (urls == null || urls.isEmpty()) {
        return newUrlInvokerMap;
    }
    Set keys = new HashSet<>();
    String queryProtocols = this.queryMap.get(PROTOCOL_KEY);

    // 遍历当前服务所有的服务提供者URL
    for (URL providerUrl : urls) {
        // If protocol is configured at the reference side, only the matching protocol is selected
        if (queryProtocols != null && queryProtocols.length() > 0) {
            boolean accept = false;
            String[] acceptProtocols = queryProtocols.split(",");

            // 当前消费者如果手动配置了Protocol，那么则进行匹配
            for (String acceptProtocol : acceptProtocols) {
                if (providerUrl.getProtocol().equals(acceptProtocol)) {
                    accept = true;
                    break;
                }
            }
            if (!accept) {
                continue;
            }
        }
        if (EMPTY_PROTOCOL.equals(providerUrl.getProtocol())) {
            continue;
        }

        // 当前Protocol是否在应用中存在对应的扩展点
        if (!ExtensionLoader.getExtensionLoader(Protocol.class).hasExtension(providerUrl.getProtocol())) {
            logger.error(...);
            continue;
        }

        URL url = mergeUrl(providerUrl);

        String key = url.toFullString(); // The parameter urls are sorted
        if (keys.contains(key)) { // Repeated url
            continue;
        }
        keys.add(key);
        // Cache key is url that does not merge with consumer side parameters, regardless of how the consumer combines parameters, if the server url changes, then refer again
        Map> localUrlInvokerMap = this.urlInvokerMap; // local reference
        Invoker invoker = localUrlInvokerMap == null ? null : localUrlInvokerMap.get(key);

        // 如果当前服务提供者URL没有生产过Invoker
        if (invoker == null) { // Not in the cache, refer again
            try {
                boolean enabled = true;
                if (url.hasParameter(DISABLED_KEY)) {
                    enabled = !url.getParameter(DISABLED_KEY, false);
                } else {
                    enabled = url.getParameter(ENABLED_KEY, true);
                }
                if (enabled) {
                    // 调用Protocol的refer方法得到一个Invoker
                    invoker = new InvokerDelegate<>(protocol.refer(serviceType, url), url, providerUrl);
                }
            } catch (Throwable t) {
                logger.error(...);
            }
            if (invoker != null) { // Put new invoker in cache
                newUrlInvokerMap.put(key, invoker);
            }
        } else {
            newUrlInvokerMap.put(key, invoker);
        }
    }
    keys.clear();
    return newUrlInvokerMap;
}