mybatis 创建Sqlsession

 

看下执行下面这行代码的时候，都发生了什么

SqlSession sqlSession = sqlSessionFactory.openSession();

第一步：org.apache.ibatis.session.defaults.DefaultSqlSessionFactory#openSession()

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

第二步：org.apache.ibatis.session.defaults.DefaultSqlSessionFactory#openSessionFromDataSource

这块代码是根据配置的Environment创建Executor。再创建DefaultSqlSession返回。

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);
        //最主要的是这里，这里创建Executor
        final Executor executor = configuration.newExecutor(tx, execType);
        //创建SqlSession并返回
        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();
    }
}

看下DefaultSqlSession的构造函数，DefaultSqlSession有一个Executor的属性。

public DefaultSqlSession(Configuration configuration, Executor executor, boolean autoCommit) {
    this.configuration = configuration;
    this.executor = executor;
    this.dirty = false;
    this.autoCommit = autoCommit;
}

---

接着就看下Executor的创建过程吧

org.apache.ibatis.session.Configuration#newExecutor(Transaction, ExecutorType)

这块代码有两点

一、根据ExecutorType创建不同的类型的Executor

也不难看出，Executor一共有三种类型

1. BatchExecutor
2. ReuseExecutor
3. SimpleExecutor（默认）

还有就是，这三种Executor都可以再次封装为CachingExecutor

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;
}

二、加载插件 executor = (Executor) interceptorChain.pluginAll(executor);

org.apache.ibatis.plugin.InterceptorChain#pluginAll

public Object pluginAll(Object target) {
    //遍历所有的插件，执行插件的plugin方法
    for (Interceptor interceptor : interceptors) {
        target = interceptor.plugin(target);
    }
    return target;
}