2021-04-11 MyBatis运行流程-02

获取SqlSession对象

具体操作

源码分析

1. openSession()

SqlSession openSession = sqlSessionFactory.openSession();

2. openSessionFromDataSource()

从configuration中拿到默认的Executor类型。Executor类型的类型有三种：SIMPLE/REUSE/BATCH。

@Override
  public SqlSession openSession() {
    return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false);
  }

3. 获取一些信息，创建事物管理器tx

private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
    Transaction tx = null;
    try {
    //从全局配置中获取环境等信息
      final Environment environment = configuration.getEnvironment();
      final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
      //创建事务
      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();
    }
  }

4. newExecutor()

传入的参数为事务管理器和Executor的类型，根据传入的类型来创建Executor，Executor是一个接口，是用来增删改查的。

final Executor executor = configuration.newExecutor(tx, execType);

5. 根据Executor在全局配置中的类型，创建出SimpleExecutor/ReuseExecutor/BatchExecutor

 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);
    }
    //看全局配置中是否配置了二级缓存，如果有用CachingExecutor包装
    if (cacheEnabled) {
      executor = new CachingExecutor(executor);
    }
    //使用拦截器包装executor
    executor = (Executor) interceptorChain.pluginAll(executor);
    return executor;
  }

6. 如果有二级缓存配置开启，创建CachingExecutor(executor)

对二级缓存的具体操作：

 public CachingExecutor(Executor delegate) {
    this.delegate = delegate;
    delegate.setExecutorWrapper(this);
  }

7. 使用每一个拦截器重新包装executor并返回

pluginAll具体实现：拿到所有的拦截器，调用每一个拦截器的plugin方法。

 public Object pluginAll(Object target) {
    for (Interceptor interceptor : interceptors) {
      target = interceptor.plugin(target);
    }
    return target;
  }

8.创建DefaultSqlSession，包含Configuration和Executor

9.返回DefaultSqlSession

总结:
DefaultSqlSession是sqlSession的实现类，里面包含了Executor和Configuration，Executor在这一步会被创建。