17. Spring类型转换之PropertyEditor

简介

我们之所以使用spring如此的简单，并且功能比较强大，比较人性化，是因为很多重复且繁琐的以及能想到的可以简化业务的功能都给我们默认提供了，类型转化就是典型的例子

spring提供了两种类型转化的方式，一种是spring提供的ConversionService，后面一篇文章再讲，另外一种就是本文要介绍的
PropertyEditor，它是jdk提供的 java.beans.PropertyEditor，spring自然也要支持

快速使用

一般的转换spring都提供了，但也不排除依然不满足我们的需要，假如现在有一个User类，使用@Value注入一个字符串，就能得到一个User，并且User的name属性就是注入的值，显然spring不知道我们有一个User类，那么就只能我们自己去实现

先看怎么使用，在分析源码

定义一个要转换的类

public class User {
	private String name;

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}
}
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定义转换器

public class String2UserPropertyEditor extends PropertyEditorSupport implements PropertyEditor {
	@Override
	public void setAsText(String text) throws IllegalArgumentException {
		User user = new User(); // 直接实例化一个User
		user.setName(text); // 设置到Name
		this.setValue(user);
	}
}
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告诉spring我们的转换器

@Configuration
public class ConvertConfig {
	@Bean
	public static CustomEditorConfigurer customEditorConfigurer() {
		CustomEditorConfigurer configurer = new CustomEditorConfigurer();
		Map<Class<?>, Class<? extends PropertyEditor>> customEditors = new HashMap<>();
		customEditors.put(User.class, String2UserPropertyEditor.class);
		configurer.setCustomEditors(customEditors);
		return configurer;
	}
}
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测试

@Component
public class UserBean implements UserGenerics {

	@Value("xx")
	private User user;

	public User getUser() {
		return user;
	}
}



public static void main(String[] args) {
    AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
    UserBean userBean = context.getBean("userBean", UserBean.class);
    System.out.println(userBean);
    System.out.println(userBean.getUser());
    System.out.println(userBean.getUser().getName());
}


输出

com.shura.beans.UserBean@668bc3d5
com.shura.convert.User@3cda1055
xx
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从上面结果可以看出确实spring给我们自动转换了。

下面就从源码看看，如何告诉spring我们需要的转换器以及spring提供的默认转换器

首先看 CustomEditorConfigurer

源码分析

public class CustomEditorConfigurer implements BeanFactoryPostProcessor, Ordered {

	protected final Log logger = LogFactory.getLog(getClass());

	private int order = Ordered.LOWEST_PRECEDENCE;

	@Nullable
	private PropertyEditorRegistrar[] propertyEditorRegistrars;

	@Nullable
	private Map<Class<?>, Class<? extends PropertyEditor>> customEditors;


	public void setOrder(int order) {
		this.order = order;
	}

	@Override
	public int getOrder() {
		return this.order;
	}

    // 添加类型转换注册器 先忽略
	public void setPropertyEditorRegistrars(PropertyEditorRegistrar[] propertyEditorRegistrars) {
		this.propertyEditorRegistrars = propertyEditorRegistrars;
	}

    // 添加类型转换器
	public void setCustomEditors(Map<Class<?>, Class<? extends PropertyEditor>> customEditors) {
		this.customEditors = customEditors;
	}

    
    // BeanFactory后置处理
	@Override
	public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
		if (this.propertyEditorRegistrars != null) {
			for (PropertyEditorRegistrar propertyEditorRegistrar : this.propertyEditorRegistrars) {
				beanFactory.addPropertyEditorRegistrar(propertyEditorRegistrar);
			}
		}
		// 将类型转换器设置到beanFactory
		if (this.customEditors != null) {
			this.customEditors.forEach(beanFactory::registerCustomEditor);
		}
	}

}
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CustomEditorConfigurer的代码比较简单，就是将我们自定义的类型转换器设置到beanFactory中，知道它是一个BeanFactoryPostProcessor就好理解了，肯定在Bean实例化之前BeanFactory就有了各种类型转换器了

spring实例化Bean的时候将每个Bean都先实例化一个 BeanWrapperImpl
org.springframework.beans.factory.support.ConstructorResolver#instantiateUsingFactoryMethod

这个类很重要，我们需要记住BeanWrapperImpl是 TypeConverterSupport PropertyEditorRegistry PropertyEditorRegistrySupport
TypeConverter的子类，并且有一个属性 TypeConverterDelegate 用来真正做转换用的

BeanWrapperImpl -> TypeConverterSupport (一个属性 TypeConverterDelegate)

// ConstructorResolver类
public BeanWrapper instantiateUsingFactoryMethod(）{
    BeanWrapperImpl bw = new BeanWrapperImpl();
	this.beanFactory.initBeanWrapper(bw);
	...
}

// AbstractBeanFactory类
protected void initBeanWrapper(BeanWrapper bw) {
    bw.setConversionService(getConversionService()); // 下节分析
    registerCustomEditors(bw); // 注册PropertyEditor 
}

protected void registerCustomEditors(PropertyEditorRegistry registry) {
    if (registry instanceof PropertyEditorRegistrySupport) {
        ((PropertyEditorRegistrySupport) registry).useConfigValueEditors();
    }
    
    
    if (!this.customEditors.isEmpty()) {
        this.customEditors.forEach((requiredType, editorClass) ->
                registry.registerCustomEditor(requiredType, BeanUtils.instantiateClass(editorClass))); // 添加到了PropertyEditorRegistrySupport
    }
}

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上面源码简单来说就是将beanFactory中自定义的PropertyEditor添加到了BeanWrapper

上面提到了BeanWrapper里面会有一个TypeConverterDelegate属性，他就是真正做转换的类，中间细节不讲了，直接看怎么转的

public <T> T convertIfNecessary(@Nullable String propertyName, @Nullable Object oldValue, @Nullable Object newValue,
			@Nullable Class<T> requiredType, @Nullable TypeDescriptor typeDescriptor) throws IllegalArgumentException {

    // 在这一步根据requiredType=User 就可以找到我们定义的 String2UserPropertyEditor 
    PropertyEditor editor = this.propertyEditorRegistry.findCustomEditor(requiredType, propertyName);

    // ... 跳过 ConversionService ...

    Object convertedValue = newValue;

    if (editor != null || (requiredType != null && !ClassUtils.isAssignableValue(requiredType, convertedValue))) {
        // 如果没有找到就从默认的propertyEditor去找
        if (editor == null) {
            editor = findDefaultEditor(requiredType);
        }
        // 转换
        convertedValue = doConvertValue(oldValue, convertedValue, requiredType, editor);
    }

    return (T) convertedValue;
}

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从上面代码可以看出就是找出前面注册的PropertyEditor，然后进行转换，转换的逻辑很简单，setText()执行一下就有了对象，然后执行getText拿到对象就行

如果没有自定义的就从默认的去找，下面就看看有哪些默认的

private PropertyEditor findDefaultEditor(@Nullable Class<?> requiredType) {
    return this.propertyEditorRegistry.getDefaultEditor(requiredType);;
}


public PropertyEditor getDefaultEditor(Class<?> requiredType) {
    if (this.defaultEditors == null) {
        createDefaultEditors();
    }
    return this.defaultEditors.get(requiredType);
}


private void createDefaultEditors() {
    this.defaultEditors = new HashMap<>(64);

    this.defaultEditors.put(Charset.class, new CharsetEditor());
    this.defaultEditors.put(Class.class, new ClassEditor());
    this.defaultEditors.put(Class[].class, new ClassArrayEditor());
    this.defaultEditors.put(Currency.class, new CurrencyEditor());
    this.defaultEditors.put(File.class, new FileEditor());
    this.defaultEditors.put(InputStream.class, new InputStreamEditor());
    if (!shouldIgnoreXml) {
        this.defaultEditors.put(InputSource.class, new InputSourceEditor());
    }
    this.defaultEditors.put(Locale.class, new LocaleEditor());
    this.defaultEditors.put(Path.class, new PathEditor());
    this.defaultEditors.put(Pattern.class, new PatternEditor());
    this.defaultEditors.put(Properties.class, new PropertiesEditor());
    this.defaultEditors.put(Reader.class, new ReaderEditor());
    this.defaultEditors.put(Resource[].class, new ResourceArrayPropertyEditor());
    this.defaultEditors.put(TimeZone.class, new TimeZoneEditor());
    this.defaultEditors.put(URI.class, new URIEditor());
    this.defaultEditors.put(URL.class, new URLEditor());
    this.defaultEditors.put(UUID.class, new UUIDEditor());
    this.defaultEditors.put(ZoneId.class, new ZoneIdEditor());

    // Default instances of collection editors.
    // Can be overridden by registering custom instances of those as custom editors.
    this.defaultEditors.put(Collection.class, new CustomCollectionEditor(Collection.class));
    this.defaultEditors.put(Set.class, new CustomCollectionEditor(Set.class));
    this.defaultEditors.put(SortedSet.class, new CustomCollectionEditor(SortedSet.class));
    this.defaultEditors.put(List.class, new CustomCollectionEditor(List.class));
    this.defaultEditors.put(SortedMap.class, new CustomMapEditor(SortedMap.class));

    // Default editors for primitive arrays.
    this.defaultEditors.put(byte[].class, new ByteArrayPropertyEditor());
    this.defaultEditors.put(char[].class, new CharArrayPropertyEditor());

    // The JDK does not contain a default editor for char!
    this.defaultEditors.put(char.class, new CharacterEditor(false));
    this.defaultEditors.put(Character.class, new CharacterEditor(true));

    // Spring's CustomBooleanEditor accepts more flag values than the JDK's default editor.
    this.defaultEditors.put(boolean.class, new CustomBooleanEditor(false));
    this.defaultEditors.put(Boolean.class, new CustomBooleanEditor(true));

    // The JDK does not contain default editors for number wrapper types!
    // Override JDK primitive number editors with our own CustomNumberEditor.
    this.defaultEditors.put(byte.class, new CustomNumberEditor(Byte.class, false));
    this.defaultEditors.put(Byte.class, new CustomNumberEditor(Byte.class, true));
    this.defaultEditors.put(short.class, new CustomNumberEditor(Short.class, false));
    this.defaultEditors.put(Short.class, new CustomNumberEditor(Short.class, true));
    this.defaultEditors.put(int.class, new CustomNumberEditor(Integer.class, false));
    this.defaultEditors.put(Integer.class, new CustomNumberEditor(Integer.class, true));
    this.defaultEditors.put(long.class, new CustomNumberEditor(Long.class, false));
    this.defaultEditors.put(Long.class, new CustomNumberEditor(Long.class, true));
    this.defaultEditors.put(float.class, new CustomNumberEditor(Float.class, false));
    this.defaultEditors.put(Float.class, new CustomNumberEditor(Float.class, true));
    this.defaultEditors.put(double.class, new CustomNumberEditor(Double.class, false));
    this.defaultEditors.put(Double.class, new CustomNumberEditor(Double.class, true));
    this.defaultEditors.put(BigDecimal.class, new CustomNumberEditor(BigDecimal.class, true));
    this.defaultEditors.put(BigInteger.class, new CustomNumberEditor(BigInteger.class, true));

    // 提供了string转数组的逻辑，我们通过配置地址的时候就会使用到
    if (this.configValueEditorsActive) {
        StringArrayPropertyEditor sae = new StringArrayPropertyEditor();
        this.defaultEditors.put(String[].class, sae);
        this.defaultEditors.put(short[].class, sae);
        this.defaultEditors.put(int[].class, sae);
        this.defaultEditors.put(long[].class, sae);
    }
}
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以上就是默认PropertyEditor的逻辑

下一篇我们介绍另外一种类型转换器 ConversionService

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