467 lines
14 KiB
Markdown
467 lines
14 KiB
Markdown
# 精尽 MyBatis 源码分析 —— 事务模块
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# 1. 概述
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本文，我们来分享 MyBatis 的事务模块，对应 `transaction` 包。如下图所示：[`transaction` 包](http://static.iocoder.cn/images/MyBatis/2020_01_19/01.png)
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在 [《精尽 MyBatis 源码解析 —— 项目结构一览》](http://svip.iocoder.cn/MyBatis/intro) 中，简单介绍了这个模块如下：
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> MyBatis 对数据库中的事务进行了抽象，其自身提供了**相应的事务接口和简单实现**。
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>
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> 在很多场景中，MyBatis 会与 Spring 框架集成，并由 **Spring 框架管理事务**。
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本文涉及的类如下图所示：[类图](http://static.iocoder.cn/images/MyBatis/2020_01_19/02.png)
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下面，我们就一起来看看具体的源码实现。
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# 2. Transaction
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`org.apache.ibatis.transaction.Transaction` ，事务接口。代码如下：
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```
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// Transaction.java
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public interface Transaction {
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/**
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* 获得连接
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*
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* Retrieve inner database connection
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*
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* @return DataBase connection
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* @throws SQLException
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*/
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Connection getConnection() throws SQLException;
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/**
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* 事务提交
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*
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* Commit inner database connection.
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*
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* @throws SQLException
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*/
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void commit() throws SQLException;
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/**
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* 事务回滚
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*
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* Rollback inner database connection.
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*
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* @throws SQLException
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*/
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void rollback() throws SQLException;
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/**
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* 关闭连接
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*
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* Close inner database connection.
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*
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* @throws SQLException
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*/
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void close() throws SQLException;
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/**
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* 获得事务超时时间
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*
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* Get transaction timeout if set
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*
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* @throws SQLException
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*/
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Integer getTimeout() throws SQLException;
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}
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```
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- 连接相关
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- `#getConnection()` 方法，获得连接。
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- `#close()` 方法，关闭连接。
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- 事务相关
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- `#commit()` 方法，事务提交。
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- `#rollback()` 方法，事务回滚。
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- `#getTimeout()` 方法，事务超时时间。实际上，目前这个方法都是空实现。
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## 2.1 JdbcTransaction
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`org.apache.ibatis.transaction.jdbc.JdbcTransaction` ，实现 Transaction 接口，基于 JDBC 的事务实现类。代码如下：
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```
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// JdbcTransaction.java
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public class JdbcTransaction implements Transaction {
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private static final Log log = LogFactory.getLog(JdbcTransaction.class);
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/**
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* Connection 对象
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*/
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protected Connection connection;
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/**
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* DataSource 对象
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*/
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protected DataSource dataSource;
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/**
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* 事务隔离级别
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*/
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protected TransactionIsolationLevel level;
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/**
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* 是否自动提交
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*/
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protected boolean autoCommit;
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public JdbcTransaction(DataSource ds, TransactionIsolationLevel desiredLevel, boolean desiredAutoCommit) {
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dataSource = ds;
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level = desiredLevel;
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autoCommit = desiredAutoCommit;
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}
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public JdbcTransaction(Connection connection) {
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this.connection = connection;
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}
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@Override
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public Connection getConnection() throws SQLException {
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// 连接为空，进行创建
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if (connection == null) {
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openConnection();
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}
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return connection;
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}
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@Override
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public void commit() throws SQLException {
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// 非自动提交，则执行提交事务
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if (connection != null && !connection.getAutoCommit()) {
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if (log.isDebugEnabled()) {
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log.debug("Committing JDBC Connection [" + connection + "]");
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}
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connection.commit();
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}
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}
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@Override
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public void rollback() throws SQLException {
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// 非自动提交。则回滚事务
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if (connection != null && !connection.getAutoCommit()) {
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if (log.isDebugEnabled()) {
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log.debug("Rolling back JDBC Connection [" + connection + "]");
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}
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connection.rollback();
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}
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}
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@Override
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public void close() throws SQLException {
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if (connection != null) {
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// 重置连接为自动提交
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resetAutoCommit();
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if (log.isDebugEnabled()) {
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log.debug("Closing JDBC Connection [" + connection + "]");
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}
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// 关闭连接
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connection.close();
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}
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}
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/**
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* 设置指定的 autoCommit 属性
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*
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* @param desiredAutoCommit 指定的 autoCommit 属性
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*/
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protected void setDesiredAutoCommit(boolean desiredAutoCommit) {
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try {
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if (connection.getAutoCommit() != desiredAutoCommit) {
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if (log.isDebugEnabled()) {
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log.debug("Setting autocommit to " + desiredAutoCommit + " on JDBC Connection [" + connection + "]");
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}
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connection.setAutoCommit(desiredAutoCommit);
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}
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} catch (SQLException e) {
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// Only a very poorly implemented driver would fail here,
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// and there's not much we can do about that.
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throw new TransactionException("Error configuring AutoCommit. "
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+ "Your driver may not support getAutoCommit() or setAutoCommit(). "
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+ "Requested setting: " + desiredAutoCommit + ". Cause: " + e, e);
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}
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}
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/**
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* 重置 autoCommit 属性
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*/
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protected void resetAutoCommit() {
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try {
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if (!connection.getAutoCommit()) {
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// MyBatis does not call commit/rollback on a connection if just selects were performed.
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// Some databases start transactions with select statements
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// and they mandate a commit/rollback before closing the connection.
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// A workaround is setting the autocommit to true before closing the connection.
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// Sybase throws an exception here.
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if (log.isDebugEnabled()) {
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log.debug("Resetting autocommit to true on JDBC Connection [" + connection + "]");
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}
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connection.setAutoCommit(true);
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}
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} catch (SQLException e) {
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if (log.isDebugEnabled()) {
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log.debug("Error resetting autocommit to true "
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+ "before closing the connection. Cause: " + e);
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}
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}
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}
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/**
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* 获得 Connection 对象
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*
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* @throws SQLException 获得失败
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*/
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protected void openConnection() throws SQLException {
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if (log.isDebugEnabled()) {
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log.debug("Opening JDBC Connection");
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}
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// 获得连接
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connection = dataSource.getConnection();
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// 设置隔离级别
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if (level != null) {
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connection.setTransactionIsolation(level.getLevel());
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}
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// 设置 autoCommit 属性
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setDesiredAutoCommit(autoCommit);
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}
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@Override
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public Integer getTimeout() throws SQLException {
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return null;
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}
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}
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```
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- 简单，胖友瞄一瞄。
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## 2.2 ManagedTransaction
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`org.apache.ibatis.transaction.managed.ManagedTransaction` ，实现 Transaction 接口，基于容器管理的事务实现类。代码如下：
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```
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// ManagedTransaction.java
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public class ManagedTransaction implements Transaction {
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private static final Log log = LogFactory.getLog(ManagedTransaction.class);
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/**
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* Connection 对象
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*/
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private Connection connection;
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/**
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* DataSource 对象
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*/
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private DataSource dataSource;
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/**
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* 事务隔离级别
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*/
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private TransactionIsolationLevel level;
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/**
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* 是否关闭连接
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*
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* 这个属性是和 {@link org.apache.ibatis.transaction.jdbc.JdbcTransaction} 不同的
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*/
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private final boolean closeConnection;
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public ManagedTransaction(Connection connection, boolean closeConnection) {
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this.connection = connection;
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this.closeConnection = closeConnection;
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}
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public ManagedTransaction(DataSource ds, TransactionIsolationLevel level, boolean closeConnection) {
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this.dataSource = ds;
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this.level = level;
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this.closeConnection = closeConnection;
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}
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@Override
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public Connection getConnection() throws SQLException {
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// 连接为空，进行创建
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if (this.connection == null) {
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openConnection();
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}
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return this.connection;
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}
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@Override
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public void commit() throws SQLException {
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// Does nothing
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}
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@Override
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public void rollback() throws SQLException {
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// Does nothing
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}
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@Override
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public void close() throws SQLException {
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// 如果开启关闭连接功能，则关闭连接
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if (this.closeConnection && this.connection != null) {
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if (log.isDebugEnabled()) {
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log.debug("Closing JDBC Connection [" + this.connection + "]");
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}
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this.connection.close();
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}
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}
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protected void openConnection() throws SQLException {
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if (log.isDebugEnabled()) {
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log.debug("Opening JDBC Connection");
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}
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// 获得连接
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this.connection = this.dataSource.getConnection();
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// 设置隔离级别
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if (this.level != null) {
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this.connection.setTransactionIsolation(this.level.getLevel());
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}
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}
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@Override
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public Integer getTimeout() throws SQLException {
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return null;
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}
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}
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```
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- 和 JdbcTransaction 相比，少了 `autoCommit` 属性，空实现 `#commit()` 和 `#rollback()` 方法。因此，事务的管理，交给了容器。
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- 简单了解下就成，实际没用过这个。
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## 2.3 SpringManagedTransaction
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`org.mybatis.spring.transaction.SpringManagedTransaction` ，实现 Transaction 接口，基于 Spring 管理的事务实现类。实际真正在使用的，本文暂时不分享，感兴趣的胖友可以自己先愁一愁 [SpringManagedTransaction](https://github.com/eddumelendez/mybatis-spring/blob/master/src/main/java/org/mybatis/spring/transaction/SpringManagedTransaction.java) 。
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# 3. TransactionFactory
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`org.apache.ibatis.transaction.TransactionFactory` ，Transaction 工厂接口。代码如下：
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```
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// TransactionFactory.java
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public interface TransactionFactory {
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/**
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* Sets transaction factory custom properties.
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*
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* 设置工厂的属性
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*
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* @param props 属性
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*/
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void setProperties(Properties props);
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/**
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* Creates a {@link Transaction} out of an existing connection.
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*
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* 创建 Transaction 事务
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*
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* @param conn Existing database connection
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* @return Transaction
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* @since 3.1.0
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*/
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Transaction newTransaction(Connection conn);
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/**
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* Creates a {@link Transaction} out of a datasource.
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*
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* 创建 Transaction 事务
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*
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* @param dataSource DataSource to take the connection from
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* @param level Desired isolation level
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* @param autoCommit Desired autocommit
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* @return Transaction
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* @since 3.1.0
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*/
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Transaction newTransaction(DataSource dataSource, TransactionIsolationLevel level, boolean autoCommit);
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}
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```
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## 3.1 JdbcTransactionFactory
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`org.apache.ibatis.transaction.jdbc.JdbcTransactionFactory` ，实现 TransactionFactory 接口，JdbcTransaction 工厂实现类。代码如下：
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```
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// JdbcTransactionFactory.java
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public class JdbcTransactionFactory implements TransactionFactory {
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@Override
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public void setProperties(Properties props) {
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}
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@Override
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public Transaction newTransaction(Connection conn) {
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// 创建 JdbcTransaction 对象
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return new JdbcTransaction(conn);
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}
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@Override
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public Transaction newTransaction(DataSource ds, TransactionIsolationLevel level, boolean autoCommit) {
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// 创建 JdbcTransaction 对象
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return new JdbcTransaction(ds, level, autoCommit);
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}
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}
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```
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- 胖友随便瞅一眼。
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## 3.2 ManagedTransactionFactory
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`org.apache.ibatis.transaction.managed.ManagedTransactionFactory` ，实现 TransactionFactory 接口，ManagedTransaction 工厂实现类。代码如下：
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```
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// ManagedTransactionFactory.java
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public class ManagedTransactionFactory implements TransactionFactory {
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/**
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* 是否关闭连接
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*/
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private boolean closeConnection = true;
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@Override
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public void setProperties(Properties props) {
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// 获得是否关闭连接属性
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if (props != null) {
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String closeConnectionProperty = props.getProperty("closeConnection");
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if (closeConnectionProperty != null) {
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closeConnection = Boolean.valueOf(closeConnectionProperty);
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}
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}
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}
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@Override
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public Transaction newTransaction(Connection conn) {
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// 创建 ManagedTransaction 对象
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return new ManagedTransaction(conn, closeConnection);
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}
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@Override
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public Transaction newTransaction(DataSource ds, TransactionIsolationLevel level, boolean autoCommit) {
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// Silently ignores autocommit and isolation level, as managed transactions are entirely
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// controlled by an external manager. It's silently ignored so that
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// code remains portable between managed and unmanaged configurations.
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// 创建 ManagedTransaction 对象
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return new ManagedTransaction(ds, level, closeConnection);
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}
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}
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```
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## 3.3 SpringManagedTransactionFactory
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`org.mybatis.spring.transaction.SpringManagedTransactionFactory` ，实现 TransactionFactory 接口，SpringManagedTransaction 工厂实现类。实际真正在使用的，本文暂时不分享，感兴趣的胖友可以自己先愁一愁 [SpringManagedTransactionFactory](https://github.com/eddumelendez/mybatis-spring/blob/c5834f93bd4a5879f86854fe188957787e56ef95/src/main/java/org/mybatis/spring/transaction/SpringManagedTransactionFactory.java) 。
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# 666. 彩蛋
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水文一篇，开心。
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参考和推荐如下文章：
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- 祖大俊 [《Mybatis3.3.x技术内幕（三）：Mybatis事务管理（将颠覆你心中目前对事务的理解）》](https://my.oschina.net/zudajun/blog/666764)
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- 徐郡明 [《MyBatis 技术内幕》](https://item.jd.com/12125531.html) 的 [「2.7 Transaction」](https://svip.iocoder.cn/MyBatis/transaction-package/#) 小节 |