MyBatis Transaction 事务接口

1、MyBatis事务介绍

Mybatis管理事务是分为两种方式：

(1)使用JDBC的事务管理机制，就是利用java.sql.Connection对象完成对事务的提交。

(2)使用MANAGED的事务管理机制，此时MyBatis自身不会去实现事务管理，而是让程序的容器（JBOSS、WebLogic）来实现对事务的管理

2、MyBatis Transaction 事务接口

Mybatis提供了一个事务接口Transaction以及两个实现类jdbcTransaction和ManagedTransaction。

2.1、Transaction接口

Transaction接口提供的抽象方法有获取数据库连接getConnection，提交事务commit，回滚事务rollback和关闭连接close。

源码如下：

public interface Transaction
{

    //获得数据库连接
    Connection getConnection() throws SQLException;

    //提交
    void commit() throws SQLException;

    //回滚
    void rollback() throws SQLException;

    //关闭连接
    void close() throws SQLException;

}

2.2、JdbcTransaction类

JdbcTransaction类通过使用JDBC提供的方式来管理事务，通过Connection提供的事务管理方法来进行事务管理。

源码如下：

public class JdbcTransaction implements Transaction
{

    /* 连接**/
    protected Connection connection;

    /* 数据源**/
    protected DataSource dataSource;

    /* 事务等级**/
    protected TransactionIsolationLevel level;

    /* 事务提交**/
    protected boolean autoCommmit;

    public JdbcTransaction(DataSource ds, TransactionIsolationLevel desiredLevel, boolean desiredAutoCommit)
    {
        dataSource = ds;
        level = desiredLevel;
        autoCommmit = desiredAutoCommit;
    }

    public JdbcTransaction(Connection connection)
    {
        this.connection = connection;
    }

    public Connection getConnection() throws SQLException
    {
        if (connection == null)
        {
            openConnection();
        }
        //返回连接
        return connection;
    }

    public void commit() throws SQLException
    {
        if (connection != null && !connection.getAutoCommit())
        {
            //连接提交
            connection.commit();
        }
    }

    public void rollback() throws SQLException
    {
        if (connection != null && !connection.getAutoCommit())
        {
            //操作回滚
            connection.rollback();
        }
    }

    public void close() throws SQLException
    {
        if (connection != null)
        {
            resetAutoCommit();

            //关闭连接
            connection.close();
        }
    }

    protected void setDesiredAutoCommit(boolean desiredAutoCommit)
    {
        try
        {
            //事务提交状态不一致时修改
            if (connection.getAutoCommit() != desiredAutoCommit)
            {
                connection.setAutoCommit(desiredAutoCommit);
            }
        }
        catch (SQLException e)
        {
            throw new TransactionException("Error configuring AutoCommit.", e);
        }
    }

    protected void resetAutoCommit()
    {
        try
        {
            if (!connection.getAutoCommit())
            {

                connection.setAutoCommit(true);
            }
        }
        catch (SQLException e)
        {

        }
    }

    protected void openConnection() throws SQLException
    {

        connection = dataSource.getConnection();
        if (level != null)
        {
            connection.setTransactionIsolation(level.getLevel());
        }
        setDesiredAutoCommit(autoCommmit);
    }

}

2.3、ManagedTransaction类

ManagedTransaction类通过容器来进行事务管理，所有它对事务提交和回滚并不会做任何操作。

源码如下：

public class ManagedTransaction implements Transaction
{

    private DataSource dataSource;
    private TransactionIsolationLevel level;
    private Connection connection;
    private boolean closeConnection;

    public ManagedTransaction(Connection connection, boolean closeConnection)
    {
        this.connection = connection;
        this.closeConnection = closeConnection;
    }

    //数据源，事务等级及是否关闭事务
    public ManagedTransaction(DataSource ds, TransactionIsolationLevel level, boolean closeConnection)
    {
        this.dataSource = ds;
        this.level = level;
        this.closeConnection = closeConnection;
    }

    public Connection getConnection() throws SQLException
    {
        if (this.connection == null)
        {
            openConnection();
        }
        return this.connection;
    }

    //提交操作
    public void commit() throws SQLException
    {
        // Does nothing
    }

    //回滚操作
    public void rollback() throws SQLException
    {
        // Does nothing
    }

    public void close() throws SQLException
    {
        if (this.closeConnection && this.connection != null)
        {
            //关闭连接
            this.connection.close();
        }
    }

    protected void openConnection() throws SQLException
    {
        this.connection = this.dataSource.getConnection();
        if (this.level != null)
        {
            this.connection.setTransactionIsolation(this.level.getLevel());
        }
    }

}

总之，Mybatis的事务管理机制还是比较简单的，其并没有做过多的操作，只是封装一下方便别人调用而已。

3、SpringManagedTransaction 类

当Spring与Mybatis一起使用时，Spring提供了一个实现类SpringManagedTransaction。它其实也是通过使用JDBC来进行事务管理的，当Spring的事务管理有效时，不需要操作commit、rollback、close，Spring事务管理会自动帮我们完成。

源码如下：

public class SpringManagedTransaction implements Transaction
{

    private final DataSource dataSource;

    private Connection connection;

    private boolean isConnectionTransactional;

    private boolean autoCommit;

    public SpringManagedTransaction(DataSource dataSource)
    {
        notNull(dataSource, "No DataSource specified");
        this.dataSource = dataSource;
    }

    public Connection getConnection() throws SQLException
    {
        if (this.connection == null)
        {
            openConnection();
        }
        return this.connection;
    }

    private void openConnection() throws SQLException
    {
        this.connection = DataSourceUtils.getConnection(this.dataSource);
        this.autoCommit = this.connection.getAutoCommit();
        this.isConnectionTransactional = DataSourceUtils.isConnectionTransactional(this.connection, this.dataSource);

    }

    public void commit() throws SQLException
    {
        if (this.connection != null && !this.isConnectionTransactional && !this.autoCommit)
        {
            this.connection.commit();
        }
    }

    public void rollback() throws SQLException
    {
        if (this.connection != null && !this.isConnectionTransactional && !this.autoCommit)
        {
            this.connection.rollback();
        }
    }

    public void close() throws SQLException
    {
        DataSourceUtils.releaseConnection(this.connection, this.dataSource);
    }

}