mybatis源码2－mapper,sqlSession,executor

一 MapperFactoryBean

1.1 MapperFactoryBean

  • spring容器中管理的dao接口bean是MapperFactoryBean
  • MapperFactoryBean.getObject()的实现是调用this.getSqlSession()获取的DefaultSqlSession的方法getMapper(this.mapperInterface);
  • DefaultSqlSession中调用的是mybatis配置的getMapper(type, this)`方法
  • mybatis配置中调用的是mapperRegistry的getMapper(type, sqlSession)方法

1.2 MapperRegistry

  • spring扫描dao接口包时，添加接口对应的代理工厂类，MapperRegistry中Map<Class<?>/*dao接口*/, MapperProxyFactory<?>> knownMappers 
public <T> void addMapper(Class<T> type) {
  if (type.isInterface()) {
    if (hasMapper(type)) {
      throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
    }
    boolean loadCompleted = false;
    try {
      knownMappers.put(type, new MapperProxyFactory<T>(type));
      // It's important that the type is added before the parser is run
      // otherwise the binding may automatically be attempted by the
      // mapper parser. If the type is already known, it won't try.
      MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
      parser.parse();
      loadCompleted = true;
    } finally {
      if (!loadCompleted) {
        knownMappers.remove(type);
      }
    }
  }
}

1.3 MapperProxy

  • 获取时使用工厂类新建实例mapperProxyFactory.newInstance(sqlSession)，即以MapperProxy为代理函数的代理类
Proxy.newProxyInstance(mapperInterface.getClassLoader(), 
        new Class[] { mapperInterface }, 
        new MapperProxy<T>(sqlSession, mapperInterface, methodCache));
  • MapperProxy使用MapperMethod代理底层不同dao接口，进行接口参数转换和返回值转换，并调用sqlsession代理接口

1.4 MapperMethod

  • 初始化
public MapperMethod(Class<?> mapperInterface, Method method, Configuration config) {
  this.command = new SqlCommand(config, mapperInterface, method);
  this.method = new MethodSignature(config, method);
}

1.4.1 SqlCommand

  • 函数对应sql指令名为接口名.方法名
  • 从mybatis配置中获取映射文件解析的sql指令对应的MappedStatement
  • 存储sql指令名称和类型
name = ms.getId();
type = ms.getSqlCommandType();

1.4.2 MethodSignature

  • 存储sql方法的参数和返回值，并提供转换方法

二 SqlSession

2.1 SqlSessionTemplate

  • SqlSession工厂代理，线程局部变量保存，线程安全。支持事务sqlSession的线程内共享。
  • 代理DefaultSqlSession的接口

2.2 DefaultSqlSession

2.2.1 初始化

  • 初始化或获取线程共享事务
  • 根据执行器类型新建sql命令执行器
  • 实例化DefaultSqlSession
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();
  }
}

2.2.2 方法

  • select*方法调用executor.query()
  • insert，update，delete调用executor.update()
  • commit，rollback，flush调用executor的对应函数

三 executor

3.1 初始化

  • 根据类型创建executor，并增加执行器插件代理。默认是SIMPLE类型。
public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
  executorType = executorType == null ? defaultExecutorType : executorType;
  executorType = executorType == null ? ExecutorType.SIMPLE : 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);
  }
  executor = (Executor) interceptorChain.pluginAll(executor);
  return executor;
}

3.2 SimpleExecutor

3.2.1 doUpdate处理流程

  • 初始化RoutingStatementHandler，添加对应的指令插件
  • Statement stmt = handler.prepare(connection);Statement预处理
  • handler.parameterize(stmt);参数设置
  • handler.update(stmt);执行更新

3.2.2 doQuery处理流程

  • 初始化RoutingStatementHandler，添加对应的指令插件
  • Statement stmt = handler.prepare(connection);Statement预处理
  • handler.parameterize(stmt);参数设置
  • handler.<E>query(stmt, resultHandler);;执行查询，resultHandler进行返回结果处理

3.3 ReuseExecutor

  • doUpdate,doQuery处理流程与SimpleExecutor相同
  • 区别是提供了Map<String, Statement> statementMap。以sql命令为key对Statement stmt的缓存
  • doFlushStatements()统一清除缓存，关闭Statement

3.4 BatchExecutor

  • 支持batch处理

3.5 BaseExecutor

  • 所有executor继承自BaseExecutor
  • update调用子类doUpdate之前，先清除本地缓存

3.5.1 query

  • 查询时执行一级缓存，SqlSession内共享，对事务性查询是线程内共享SqlSession，也就是共享一级缓存数据。
  • 先判断flushCache配置，为true，则先清空缓存，默认为false
  • 查询缓存以key存储,CacheKey key = createCacheKey(ms, parameter, rowBounds, boundSql)
  • 存在缓存，则不再执行sql查询。缓存参数localOutputParameterCache转换后返回handleLocallyCachedOutputParameters()
  • deferredLoads延迟加载处理
  • configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT 语句级范围则请求完成后清除缓存，session范围缓存则可用。

3.6 CachingExecutor

  • SqlSession存储的执行器实际是CachingExecutor，内部代理了SimpleExecutor.
  • CachingExecutor实现了mybatis的二级缓存功能，缓存数据存储在MappedStatement中，Cache cache = ms.getCache();
  • MappedStatement是多个SqlSession共享的，即二级缓存是共享实用的。
  • 查询时，若配置使用二级缓存则先取缓存中数据

四 插件

  • 在mybatis配置中使用InterceptorChain interceptorChain保存所有插件配置

4.1 InterceptorChain

  • 使用List<Interceptor> interceptors存储所有插件
  • 调用插件方法target = interceptor.plugin(target);，对目标类创建插件代理，一般内部实现使用org.apache.ibatis.plugin.Plugin创建代理。

4.2 Plugin

  • 创建代理
public static Object wrap(Object target, Interceptor interceptor) {
  Map<Class<?>, Set<Method>> signatureMap = getSignatureMap(interceptor);
  Class<?> type = target.getClass();
  Class<?>[] interfaces = getAllInterfaces(type, signatureMap);
  if (interfaces.length > 0) {
    return Proxy.newProxyInstance(
        type.getClassLoader(),
        interfaces,
        new Plugin(target, interceptor, signatureMap));
  }
  return target;
}
  • 拦截方法内，则调用插件的intercept方法，执行插件处理。
Set<Method> methods = signatureMap.get(method.getDeclaringClass());
if (methods != null && methods.contains(method)) {
  return interceptor.intercept(new Invocation(target, method, args));
}
  • 不在拦截方法内，则直接调用目标方法。return method.invoke(target, args);

4.3 插件类型

  • 插件分为Executor执行器插件，ParameterHandler参数处理插件，ResultSetHandler结果处理插件，StatementHandler预处理插件。
  • interceptor.plugin(target)创建插件代理时，需要判断target是否是期望的插件目标点
  • ParameterHandler参数处理插件
public ParameterHandler newParameterHandler(MappedStatement mappedStatement, Object parameterObject, BoundSql boundSql) {
  ParameterHandler parameterHandler = mappedStatement.getLang().createParameterHandler(mappedStatement, parameterObject, boundSql);
  parameterHandler = (ParameterHandler) interceptorChain.pluginAll(parameterHandler);
  return parameterHandler;
}
  • ResultSetHandler结果处理插件
    ResultHandler resultHandler, BoundSql boundSql) {
  ResultSetHandler resultSetHandler = new DefaultResultSetHandler(executor, mappedStatement, parameterHandler, resultHandler, boundSql, rowBounds);
  resultSetHandler = (ResultSetHandler) interceptorChain.pluginAll(resultSetHandler);
  return resultSetHandler;
}
  • StatementHandler预处理插件
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);
  statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);
  return statementHandler;
}
  • Executor执行器插件，在根据执行器类型newExecutor新建执行器时，创建executor = (Executor) interceptorChain.pluginAll(executor);
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