MyBatis事务管理机制
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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,这种机制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 在Mybatis的配置文件中可以配置事务管理方式如下: [html] view plain copy <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"> <configuration> <environments default="development"> <environment id="development"> <!--配置事务的管理方式--> <transactionManager type="JDBC" /> <!-- 配置数据库连接信息 --> <dataSource type="POOLED"> <property name="driver" value="com.mysql.jdbc.Driver" /> <property name="url" value="jdbc:mysql://localhost:3306/mybatis" /> <property name="username" value="root" /> <property name="password" value="XDP" /> </dataSource> </environment> </environments> </configuration> Mybatis提供了一个事务接口Transaction,以及两个实现类jdbcTransaction和ManagedTransaction,当spring与Mybatis一起使用时,spring提供了一个实现类SpringManagedTransaction 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: [java] view plain copy //事务接口 ublic interface Transaction { /** * Retrieve inner database connection * @return DataBase connection * @throws SQLException */ //获得数据库连接 Connection getConnection() throws SQLException; /** * 提交 * Commit inner database connection. * @throws SQLException */ void commit() throws SQLException; /** * 回滚 * Rollback inner database connection. * @throws SQLException */ void rollback() throws SQLException; /** * 关闭连接 * Close inner database connection. * @throws SQLException */ void close() throws SQLException; JdbcTransaction实现类:Transaction的实现类,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: [java] view plain copy public class JdbcTransaction implements Transaction { private static final Log log = LogFactory.getLog(JdbcTransaction.class); /* 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; } @Override public Connection getConnection() throws SQLException { if (connection == null) { openConnection(); } //返回连接 return connection; } @Override public void commit() throws SQLException { if (connection != null && !connection.getAutoCommit()) { if (log.isDebugEnabled()) { log.debug("Committing JDBC Connection [" + connection + "]"); } //连接提交 connection.commit(); } } @Override public void rollback() throws SQLException { if (connection != null && !connection.getAutoCommit()) { if (log.isDebugEnabled()) { log.debug("Rolling back JDBC Connection [" + connection + "]"); } //连接回滚 connection.rollback(); } } @Override public void close() throws SQLException { if (connection != null) { resetAutoCommit(); if (log.isDebugEnabled()) { log.debug("Closing JDBC Connection [" + connection + "]"); } //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) { if (log.isDebugEnabled()) { log.debug("Setting autocommit to " + desiredAutoCommit + " on JDBC Connection [" + connection + "]"); } connection.setAutoCommit(desiredAutoCommit); } } catch (SQLException e) { // Only a very poorly implemented driver would fail here, // and there's not much we can do about that. throw new TransactionException("Error configuring AutoCommit. " + "Your driver may not support getAutoCommit() or setAutoCommit(). " + "Requested setting: " + desiredAutoCommit + ". Cause: " + e, e); } } protected void resetAutoCommit() { try { if (!connection.getAutoCommit()) { // MyBatis does not call commit/rollback on a connection if just selects were performed. select操作没有commit和rollback事务 // Some databases start transactions with select statements 一些数据库在select操作是会开启事务 // and they mandate a commit/rollback before closing the connection. // A workaround is setting the autocommit to true before closing the connection. // Sybase throws an exception here. if (log.isDebugEnabled()) { log.debug("Resetting autocommit to true on JDBC Connection [" + connection + "]"); } connection.setAutoCommit(true); } } catch (SQLException e) { if (log.isDebugEnabled()) { log.debug("Error resetting autocommit to true " + "before closing the connection. Cause: " + e); } } } //打开连接 protected void openConnection() throws SQLException { if (log.isDebugEnabled()) { log.debug("Opening JDBC Connection"); } //从数据源中获得连接 connection = dataSource.getConnection(); if (level != null) { connection.setTransactionIsolation(level.getLevel()); } setDesiredAutoCommit(autoCommmit); } } ManagedTransaction实现类: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: [java] view plain copy public class ManagedTransaction implements Transaction { private static final Log log = LogFactory.getLog(ManagedTransaction.class); 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; } @Override public Connection getConnection() throws SQLException { if (this.connection == null) { openConnection(); } return this.connection; } //提交操作无效 @Override public void commit() throws SQLException { // Does nothing } //回滚操作无效 @Override public void rollback() throws SQLException { // Does nothing } @Override public void close() throws SQLException { if (this.closeConnection && this.connection != null) { if (log.isDebugEnabled()) { log.debug("Closing JDBC Connection [" + this.connection + "]"); } //关闭连接 this.connection.close(); } } protected void openConnection() throws SQLException { if (log.isDebugEnabled()) { log.debug("Opening JDBC Connection"); } this.connection = this.dataSource.getConnection(); if (this.level != null) { this.connection.setTransactionIsolation(this.level.getLevel()); } } } SpringManagedTransaction实现类: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: [java] view plain copy public class SpringManagedTransaction implements Transaction { private static final Log LOGGER = LogFactory.getLog(SpringManagedTransaction.class); private final DataSource dataSource; private Connection connection; private boolean isConnectionTransactional; private boolean autoCommit; //获得数据源 public SpringManagedTransaction(DataSource dataSource) { notNull(dataSource, "No DataSource specified"); this.dataSource = dataSource; } /** * {@inheritDoc} * 返回数据库连接 */ @Override public Connection getConnection() throws SQLException { if (this.connection == null) { openConnection(); } return this.connection; } /** * Gets a connection from Spring transaction manager and discovers if this * {@code Transaction} should manage connection or let it to Spring. * <p> * It also reads autocommit setting because when using Spring Transaction MyBatis * thinks that autocommit is always false and will always call commit/rollback * so we need to no-op that calls. *从spring的事务管理中获得一个连接 */ private void openConnection() throws SQLException { this.connection = DataSourceUtils.getConnection(this.dataSource); this.autoCommit = this.connection.getAutoCommit(); this.isConnectionTransactional = DataSourceUtils.isConnectionTransactional(this.connection, this.dataSource); if (LOGGER.isDebugEnabled()) { LOGGER.debug( "JDBC Connection [" + this.connection + "] will" + (this.isConnectionTransactional ? " " : " not ") + "be managed by Spring"); } } /** * {@inheritDoc} */ @Override public void commit() throws SQLException { if (this.connection != null && !this.isConnectionTransactional && !this.autoCommit) { if (LOGGER.isDebugEnabled()) { LOGGER.debug("Committing JDBC Connection [" + this.connection + "]"); } this.connection.commit(); } } /** * {@inheritDoc} */ @Override public void rollback() throws SQLException { if (this.connection != null && !this.isConnectionTransactional && !this.autoCommit) { if (LOGGER.isDebugEnabled()) { LOGGER.debug("Rolling back JDBC Connection [" + this.connection + "]"); } this.connection.rollback(); } } /** * {@inheritDoc} */ @Override public void close() throws SQLException { DataSourceUtils.releaseConnection(this.connection, this.dataSource); } }
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