Mybatis源码的理解

0.核心的包

# 1.Configuration类

1.1 配置文件mybatis-config.xml

DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>

    
    <properties resource="db.properties">properties>
 
    <settings>
        
        <setting name="logImpl" value="STDOUT_LOGGING"/>
        
        <setting name="cacheEnabled" value="true"/>
    settings>
    
    <environments default="development">
        <environment id="development">
              <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            dataSource>
        environment>
    environments>
    <mappers>
        <mapper resource="mapper/PersonMapper.xml"/>
    mappers>
configuration>
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1.2 配置文件解析

将配置文件转化为输入流,最终将 xml转化Configuration类.

将配置文件转化为输入流,将 xml转化Configuration类.

//XMLConfigBuilder  解析器
XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
//将xml转化为Document
public XPathParser(InputStream inputStream, boolean validation, Properties variables, EntityResolver entityResolver) {
    commonConstructor(validation, variables, entityResolver);
    this.document = createDocument(new InputSource(inputStream));
}
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解析配置对应的标签为Configuration的属性

 private void parseConfiguration(XNode root) {
    try {
      // issue #117 read properties first
      propertiesElement(root.evalNode("properties"));
      Properties settings = settingsAsProperties(root.evalNode("settings"));
      loadCustomVfs(settings);
      loadCustomLogImpl(settings);
      typeAliasesElement(root.evalNode("typeAliases"));
      pluginElement(root.evalNode("plugins"));
      objectFactoryElement(root.evalNode("objectFactory"));
      objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
      reflectorFactoryElement(root.evalNode("reflectorFactory"));
      settingsElement(settings);
      // read it after objectFactory and objectWrapperFactory issue #631
      environmentsElement(root.evalNode("environments"));
      databaseIdProviderElement(root.evalNode("databaseIdProvider"));
      typeHandlerElement(root.evalNode("typeHandlers"));
      mapperElement(root.evalNode("mappers"));
    } catch (Exception e) {
      throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
    }
  }
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Configuration的核心类的属性

public class Configuration {
  //加载环境
  protected Environment environment;
  //是否开启缓存
  protected boolean cacheEnabled = true;
  //配置日志的实现
  protected Class<? extends Log> logImpl;
  //配置属性Properties 
  protected Properties variables = new Properties();
  protected ObjectFactory objectFactory = new DefaultObjectFactory();
  protected ObjectWrapperFactory objectWrapperFactory = new DefaultObjectWrapperFactory();
  ///代理工厂 
  protected ProxyFactory proxyFactory = new JavassistProxyFactory();
  //数据库ID
  protected String databaseId;
  //mapper注册
  protected final MapperRegistry mapperRegistry = new MapperRegistry(this);
  //拦截器注册类
  protected final InterceptorChain interceptorChain = new InterceptorChain();
  //类型处理器
  protected final TypeHandlerRegistry typeHandlerRegistry = new TypeHandlerRegistry(this);
  //类别名注册
  protected final TypeAliasRegistry typeAliasRegistry = new TypeAliasRegistry();
//加载映射的mapper xml
  protected final Map<String, MappedStatement> mappedStatements = new StrictMap<MappedStatement>(
      "Mapped Statements collection")
          .conflictMessageProducer((savedValue, targetValue) -> ". please check " + savedValue.getResource() + " and "
              + targetValue.getResource());
 //加载的缓存
  protected final Map<String, Cache> caches = new StrictMap<>("Caches collection");
  //xml结果集
  protected final Map<String, ResultMap> resultMaps = new StrictMap<>("Result Maps collection");
  //参数的
  protected final Map<String, ParameterMap> parameterMaps = new StrictMap<>("Parameter Maps collection");
  //主键生成器 
  protected final Map<String, KeyGenerator> keyGenerators = new StrictMap<>("Key Generators collection");
  ///sql片段
  protected final Map<String, XNode> sqlFragments = new StrictMap<>("XML fragments parsed from previous mappers");


  public ParameterHandler newParameterHandler(MappedStatement mappedStatement, Object parameterObject,
      BoundSql boundSql) {
    ParameterHandler parameterHandler = mappedStatement.getLang().createParameterHandler(mappedStatement,
        parameterObject, boundSql);
    return (ParameterHandler) interceptorChain.pluginAll(parameterHandler);
  }
// ResultSetHandler  结果集处理
  public ResultSetHandler newResultSetHandler(Executor executor, MappedStatement mappedStatement, RowBounds rowBounds,
      ParameterHandler parameterHandler, ResultHandler resultHandler, BoundSql boundSql) {
    ResultSetHandler resultSetHandler = new DefaultResultSetHandler(executor, mappedStatement, parameterHandler,
        resultHandler, boundSql, rowBounds);
    return (ResultSetHandler) interceptorChain.pluginAll(resultSetHandler);
  }

  public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement,
      Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
    StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject,
        rowBounds, resultHandler, boundSql);
    return (StatementHandler) interceptorChain.pluginAll(statementHandler);
  }

  public Executor newExecutor(Transaction transaction) {
    return newExecutor(transaction, defaultExecutorType);
  }
  //获取执行器
  public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
    executorType = executorType == null ? defaultExecutorType : executorType;
    Executor executor;
    if (ExecutorType.BATCH == executorType) {
      executor = new BatchExecutor(this, transaction);
    } else if (ExecutorType.REUSE == executorType) {
      executor = new ReuseExecutor(this, transaction);
    } else {
      executor = new SimpleExecutor(this, transaction);
    }
    if (cacheEnabled) {
      executor = new CachingExecutor(executor);
    }
    return (Executor) interceptorChain.pluginAll(executor);
  }

  //获取注册mapper类
  public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    return mapperRegistry.getMapper(type, sqlSession);
  }
}

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1.3 解析完成查询之后的configuration

public Configuration parse() {
    if (parsed) {
      throw new BuilderException("Each XMLConfigBuilder can only be used once.");
    }
    parsed = true;
    parseConfiguration(parser.evalNode("/configuration"));
    return configuration;
  }
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environment类

sqlFragments类

mapperRegistry类

mapperStatements

caches类

2.SQL解析

sql的解析有两种，一个是标签注解，一个是xml配置文件的解析。对应的映射解析器为XMLMapperBuilder和MapperAnnotationBuilder

2.1 XMLMapperBuilder

属性

 private final XPathParser parser;
 //辅助构建类
 private final MapperBuilderAssistant builderAssistant;
 //加载的sql片段
 private final Map<String, XNode> sqlFragments;
 private final String resource;
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解析文件的mapper的命名空间，缓存，参数,结果集以及sql.

private void configurationElement(XNode context) {
    try {
      String namespace = context.getStringAttribute("namespace");
      if (namespace == null || namespace.isEmpty()) {
        throw new BuilderException("Mapper's namespace cannot be empty");
      }
      builderAssistant.setCurrentNamespace(namespace);
      cacheRefElement(context.evalNode("cache-ref"));
      cacheElement(context.evalNode("cache"));
      parameterMapElement(context.evalNodes("/mapper/parameterMap"));
      resultMapElements(context.evalNodes("/mapper/resultMap"));
      sqlElement(context.evalNodes("/mapper/sql"));
      buildStatementFromContext(context.evalNodes("select|insert|update|delete"));
    } catch (Exception e) {
      throw new BuilderException("Error parsing Mapper XML. The XML location is '" + resource + "'. Cause: " + e, e);
    }
  }
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解析参数parameterMap

private void parameterMapElement(List<XNode> list) {
    for (XNode parameterMapNode : list) {
      String id = parameterMapNode.getStringAttribute("id");
      String type = parameterMapNode.getStringAttribute("type");
      Class<?> parameterClass = resolveClass(type);
      List<XNode> parameterNodes = parameterMapNode.evalNodes("parameter");
      List<ParameterMapping> parameterMappings = new ArrayList<>();
      for (XNode parameterNode : parameterNodes) {
        String property = parameterNode.getStringAttribute("property");
        String javaType = parameterNode.getStringAttribute("javaType");
        String jdbcType = parameterNode.getStringAttribute("jdbcType");
        String resultMap = parameterNode.getStringAttribute("resultMap");
        String mode = parameterNode.getStringAttribute("mode");
        String typeHandler = parameterNode.getStringAttribute("typeHandler");
        Integer numericScale = parameterNode.getIntAttribute("numericScale");
        ParameterMode modeEnum = resolveParameterMode(mode);
        Class<?> javaTypeClass = resolveClass(javaType);
        JdbcType jdbcTypeEnum = resolveJdbcType(jdbcType);
        Class<? extends TypeHandler<?>> typeHandlerClass = resolveClass(typeHandler);
        ParameterMapping parameterMapping = builderAssistant.buildParameterMapping(parameterClass, property, javaTypeClass, jdbcTypeEnum, resultMap, modeEnum, typeHandlerClass, numericScale);
        parameterMappings.add(parameterMapping);
      }
      builderAssistant.addParameterMap(id, parameterClass, parameterMappings);
    }
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解析sql片段

2.2 MapperAnnotationBuilder

3. SQL执行:

3.1 获取SqlSession 以及获取执行器

 private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level,
      boolean autoCommit) {
    Transaction tx = null;
    try {
      final Environment environment = configuration.getEnvironment();
      final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
      tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
      final Executor executor = configuration.newExecutor(tx, execType);
      return new DefaultSqlSession(configuration, executor, autoCommit);
    } catch (Exception e) {
      closeTransaction(tx); // may have fetched a connection so lets call close()
      throw ExceptionFactory.wrapException("Error opening session.  Cause: " + e, e);
    } finally {
      ErrorContext.instance().reset();
    }
  }
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3.2 Executor【SimpleExecutor ReuseExecutor】

接口–》Executor --》 SimpleExecutor ReuseExecutor 【Statement–JDBC】

executorType类型

public enum ExecutorType {
  SIMPLE,
  REUSE,
  BATCH
}
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根据类型获取执行器

public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
    executorType = executorType == null ? defaultExecutorType : executorType;
    Executor executor;
    if (ExecutorType.BATCH == executorType) {
      executor = new BatchExecutor(this, transaction);
    } else if (ExecutorType.REUSE == executorType) {
      executor = new ReuseExecutor(this, transaction);
    } else {
      executor = new SimpleExecutor(this, transaction);
    }
    if (cacheEnabled) {
      executor = new CachingExecutor(executor);
    }
    return (Executor) interceptorChain.pluginAll(executor);
  }
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执行sql语句

从配置文件拿到执行的语句

  private <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds, ResultHandler handler) {
    try {
      MappedStatement ms = configuration.getMappedStatement(statement);
      dirty |= ms.isDirtySelect();
      return executor.query(ms, wrapCollection(parameter), rowBounds, handler);
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error querying database.  Cause: " + e, e);
    } finally {
      ErrorContext.instance().reset();
    }
  }
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  public RoutingStatementHandler(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds,
      ResultHandler resultHandler, BoundSql boundSql) {

    switch (ms.getStatementType()) {
      case STATEMENT:
        delegate = new SimpleStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
        break;
      case PREPARED:
        delegate = new PreparedStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
        break;
      case CALLABLE:
        delegate = new CallableStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
        break;
      default:
        throw new ExecutorException("Unknown statement type: " + ms.getStatementType());
    }

  }
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jdbc执行

4. 结果映射：ResultSetHandler

4.1 执行拿到返回结果进行处理

  @Override
  public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
    PreparedStatement ps = (PreparedStatement) statement;
    ps.execute();
    return resultSetHandler.handleResultSets(ps);
  }
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执行返回的数据

4.2 resultSetHandler.handleResultSets(ps)

结果处理

 public List<Object> handleResultSets(Statement stmt) throws SQLException {
    ErrorContext.instance().activity("handling results").object(mappedStatement.getId());

    final List<Object> multipleResults = new ArrayList<>();

    int resultSetCount = 0;
    ResultSetWrapper rsw = getFirstResultSet(stmt);

    List<ResultMap> resultMaps = mappedStatement.getResultMaps();
    int resultMapCount = resultMaps.size();
    validateResultMapsCount(rsw, resultMapCount);
    while (rsw != null && resultMapCount > resultSetCount) {
      ResultMap resultMap = resultMaps.get(resultSetCount);
      handleResultSet(rsw, resultMap, multipleResults, null);
      rsw = getNextResultSet(stmt);
      cleanUpAfterHandlingResultSet();
      resultSetCount++;
    }

    String[] resultSets = mappedStatement.getResultSets();
    if (resultSets != null) {
      while (rsw != null && resultSetCount < resultSets.length) {
        ResultMapping parentMapping = nextResultMaps.get(resultSets[resultSetCount]);
        if (parentMapping != null) {
          String nestedResultMapId = parentMapping.getNestedResultMapId();
          ResultMap resultMap = configuration.getResultMap(nestedResultMapId);
          handleResultSet(rsw, resultMap, null, parentMapping);
        }
        rsw = getNextResultSet(stmt);
        cleanUpAfterHandlingResultSet();
        resultSetCount++;
      }
    }

    return collapseSingleResultList(multipleResults);
  }
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