MyBatis-Spring中实现spring事务管理解析

        我们在使用Mybatis时会配置SqlSessionFactoryBean用于创建SqlSessionFactory，在buildSqlSessionFactory()方法中我们就可以看到TransactionFactory的创建，TransactionFactory就是事务管理的基础。TransactionFactory也是可以在配置中配置的，如果没配置就使用SpringManagedTransactionFactory，SpringManagedTransactionFactory功能就创建SpringManagedTransaction事务管理对象来管理Mybatis中的数据库事务。

1、SqlSessionFactoryBean.buildSqlSessionFactory()

protected SqlSessionFactory buildSqlSessionFactory() throws IOException {
    //Mybatis全局配置
    Configuration configuration;
    
    .................

    if (this.transactionFactory == null) {
      // 默认使用SpringManagedTransactionFactory
      this.transactionFactory = new SpringManagedTransactionFactory();
    }
    // 把transactionFactory保存在Configuration中，便于其它地方获取使用
    Environment environment = new Environment(this.environment, this.transactionFactory, this.dataSource);
    configuration.setEnvironment(environment);

    .................
    
    //根据全局配置创建SqlSessionFactory
    return this.sqlSessionFactoryBuilder.build(configuration);
}

 

2、SpringManagedTransaction.openConnection()

//在获取数据库连接时调用的方法
private void openConnection() throws SQLException {
    //通过spring的DataSourceUtils工具类获取数据连接
    this.connection = DataSourceUtils.getConnection(this.dataSource);
    this.autoCommit = this.connection.getAutoCommit();
    this.isConnectionTransactional = isConnectionTransactional(this.connection, this.dataSource);

    ................
}

 

3、DataSourceUtils.doGetConnection()

//最终获取数据库连接的方法
public static Connection doGetConnection(DataSource dataSource) throws SQLException {
    Assert.notNull(dataSource, "No DataSource specified");
    //spring事务管理一个核心类TransactionSynchronizationManager，TransactionSynchronizationManager里面通过ThreadLocal变量保存了dataSource对应的ConnectionHolder，实现了spring的事务传播特性。
    ConnectionHolder conHolder = (ConnectionHolder) TransactionSynchronizationManager.getResource(dataSource);
    if (conHolder != null && (conHolder.hasConnection() || conHolder.isSynchronizedWithTransaction())) {
        conHolder.requested();
        if (!conHolder.hasConnection()) {
            logger.debug("Fetching resumed JDBC Connection from DataSource");
            conHolder.setConnection(dataSource.getConnection());
        }
        return conHolder.getConnection();
    }
    // Else we either got no holder or an empty thread-bound holder here.
    logger.debug("Fetching JDBC Connection from DataSource");
    Connection con = dataSource.getConnection();
    if (TransactionSynchronizationManager.isSynchronizationActive()) {
        logger.debug("Registering transaction synchronization for JDBC Connection");
        // Use same Connection for further JDBC actions within the transaction.
        // Thread-bound object will get removed by synchronization at transaction completion.
        ConnectionHolder holderToUse = conHolder;
        if (holderToUse == null) {
            holderToUse = new ConnectionHolder(con);
        }
        else {
            holderToUse.setConnection(con);
        }
        holderToUse.requested();
        TransactionSynchronizationManager.registerSynchronization(
                new ConnectionSynchronization(holderToUse, dataSource));
        holderToUse.setSynchronizedWithTransaction(true);
        if (holderToUse != conHolder) {
            TransactionSynchronizationManager.bindResource(dataSource, holderToUse);
        }
    }
    return con;
}