DataSourceTransactionManager

doGetTransaction

isExistingTransaction

doBegin

doCommit

doSuspend

doRollback

doCleanupAfterCompletion

DataSourceUtils

ConnectionSynchronization

suspend

JDBC事务时Spring 事务的具体实现。

DataSourceTransactionManager

public class DataSourceTransactionManager extends AbstractPlatformTransactionManagerimplements ResourceTransactionManager, InitializingBean {//数据库DataSourceprivate DataSource dataSource;private boolean enforceReadOnly = false;
}

doGetTransaction

构造DataSourceTransactionObject，存储ConnectionHolder 。

 @Overrideprotected Object doGetTransaction() {DataSourceTransactionObject txObject = new DataSourceTransactionObject();txObject.setSavepointAllowed(isNestedTransactionAllowed());
//通过DataSource获取ConnectionHolder ConnectionHolder conHolder =(ConnectionHolder) TransactionSynchronizationManager.getResource(obtainDataSource());
//DataSourceTransactionObject设置ConnectionHolder txObject.setConnectionHolder(conHolder, false);return txObject;}

isExistingTransaction

如果存在getConnectionHolder，并且有活跃事务，则表示已存在事务。

 @Overrideprotected boolean isExistingTransaction(Object transaction) {DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;return (txObject.hasConnectionHolder() && txObject.getConnectionHolder().isTransactionActive());}

doBegin

主要功能就是保存Connection，设置事务状态。

@Overrideprotected void doBegin(Object transaction, TransactionDefinition definition) {//获取事务对象。DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;Connection con = null;try {//如果没有ConnectionHolder，则构造一个。if (!txObject.hasConnectionHolder() ||txObject.getConnectionHolder().isSynchronizedWithTransaction()) {Connection newCon = obtainDataSource().getConnection();if (logger.isDebugEnabled()) {logger.debug("Acquired Connection [" + newCon + "] for JDBC transaction");}txObject.setConnectionHolder(new ConnectionHolder(newCon), true);}txObject.getConnectionHolder().setSynchronizedWithTransaction(true);//从事务对象获取Connectioncon = txObject.getConnectionHolder().getConnection();//事务准备，返回隔离级别，并设置到当前事务对象。Integer previousIsolationLevel = DataSourceUtils.prepareConnectionForTransaction(con, definition);txObject.setPreviousIsolationLevel(previousIsolationLevel);txObject.setReadOnly(definition.isReadOnly());// Switch to manual commit if necessary. This is very expensive in some JDBC drivers,// so we don't want to do it unnecessarily (for example if we've explicitly// configured the connection pool to set it already).//是否自动提交。如果是自动提交，则改为手动提交。if (con.getAutoCommit()) {txObject.setMustRestoreAutoCommit(true);if (logger.isDebugEnabled()) {logger.debug("Switching JDBC Connection [" + con + "] to manual commit");}con.setAutoCommit(false);}//准备提交。prepareTransactionalConnection(con, definition);//激活当前事务。txObject.getConnectionHolder().setTransactionActive(true);//设置超时。int timeout = determineTimeout(definition);if (timeout != TransactionDefinition.TIMEOUT_DEFAULT) {txObject.getConnectionHolder().setTimeoutInSeconds(timeout);}// 如果是新建的，则绑定到当前线程。if (txObject.isNewConnectionHolder()) {TransactionSynchronizationManager.bindResource(obtainDataSource(), txObject.getConnectionHolder());}}catch (Throwable ex) {if (txObject.isNewConnectionHolder()) {DataSourceUtils.releaseConnection(con, obtainDataSource());txObject.setConnectionHolder(null, false);}throw new CannotCreateTransactionException("Could not open JDBC Connection for transaction", ex);}}

doCommit

通过事务的Connection，调用commit方法，提交事务。

@Overrideprotected void doCommit(DefaultTransactionStatus status) {
//从事务对象中获取Connection，调用Connection的提交。DataSourceTransactionObject txObject = (DataSourceTransactionObject) status.getTransaction();Connection con = txObject.getConnectionHolder().getConnection();if (status.isDebug()) {logger.debug("Committing JDBC transaction on Connection [" + con + "]");}try {con.commit();}catch (SQLException ex) {throw new TransactionSystemException("Could not commit JDBC transaction", ex);}}

doSuspend

Connection设置为null，解绑资源

 @Overrideprotected Object doSuspend(Object transaction) {DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;txObject.setConnectionHolder(null);
//当前线程解绑资源，return TransactionSynchronizationManager.unbindResource(obtainDataSource());}@Overrideprotected void doResume(@Nullable Object transaction, Object suspendedResources) {
//重新绑定资源TransactionSynchronizationManager.bindResource(obtainDataSource(), suspendedResources);}

doRollback

调用Connection.rollback()方法回滚事务。

@Overrideprotected void doRollback(DefaultTransactionStatus status) {DataSourceTransactionObject txObject = (DataSourceTransactionObject) status.getTransaction();Connection con = txObject.getConnectionHolder().getConnection();if (status.isDebug()) {logger.debug("Rolling back JDBC transaction on Connection [" + con + "]");}try {con.rollback();}catch (SQLException ex) {throw new TransactionSystemException("Could not roll back JDBC transaction", ex);}}

doCleanupAfterCompletion

如果新事务，解绑资源。恢复状态：自动提交、connection。

 @Overrideprotected void doCleanupAfterCompletion(Object transaction) {DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;// Remove the connection holder from the thread, if exposed.if (txObject.isNewConnectionHolder()) {TransactionSynchronizationManager.unbindResource(obtainDataSource());}// Reset connection.Connection con = txObject.getConnectionHolder().getConnection();try {if (txObject.isMustRestoreAutoCommit()) {con.setAutoCommit(true);}DataSourceUtils.resetConnectionAfterTransaction(con, txObject.getPreviousIsolationLevel(), txObject.isReadOnly());}catch (Throwable ex) {logger.debug("Could not reset JDBC Connection after transaction", ex);}if (txObject.isNewConnectionHolder()) {if (logger.isDebugEnabled()) {logger.debug("Releasing JDBC Connection [" + con + "] after transaction");}DataSourceUtils.releaseConnection(con, this.dataSource);}txObject.getConnectionHolder().clear();}

DataSourceUtils

DataSourceUtils，工具类，用于辅助DataSource操作。主要就是Connection相关操作，

ConnectionSynchronization

用于事务同步。

private final ConnectionHolder connectionHolder;private final DataSource dataSource;private int order;private boolean holderActive = true;

suspend

解绑datasource资源，释放connection。

 @Overridepublic void suspend() {if (this.holderActive) {TransactionSynchronizationManager.unbindResource(this.dataSource);if (this.connectionHolder.hasConnection() && !this.connectionHolder.isOpen()) {// Release Connection on suspend if the application doesn't keep// a handle to it anymore. We will fetch a fresh Connection if the// application accesses the ConnectionHolder again after resume,// assuming that it will participate in the same transaction.releaseConnection(this.connectionHolder.getConnection(), this.dataSource);this.connectionHolder.setConnection(null);}}}

 @Overridepublic void resume() {if (this.holderActive) {TransactionSynchronizationManager.bindResource(this.dataSource, this.connectionHolder);}}

@Overridepublic void beforeCompletion() {// Release Connection early if the holder is not open anymore// (that is, not used by another resource like a Hibernate Session// that has its own cleanup via transaction synchronization),// to avoid issues with strict JTA implementations that expect// the close call before transaction completion.if (!this.connectionHolder.isOpen()) {TransactionSynchronizationManager.unbindResource(this.dataSource);this.holderActive = false;if (this.connectionHolder.hasConnection()) {releaseConnection(this.connectionHolder.getConnection(), this.dataSource);}}}@Overridepublic void afterCompletion(int status) {// If we haven't closed the Connection in beforeCompletion,// close it now. The holder might have been used for other// cleanup in the meantime, for example by a Hibernate Session.if (this.holderActive) {// The thread-bound ConnectionHolder might not be available anymore,// since afterCompletion might get called from a different thread.TransactionSynchronizationManager.unbindResourceIfPossible(this.dataSource);this.holderActive = false;if (this.connectionHolder.hasConnection()) {releaseConnection(this.connectionHolder.getConnection(), this.dataSource);// Reset the ConnectionHolder: It might remain bound to the thread.this.connectionHolder.setConnection(null);}}this.connectionHolder.reset();}

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DataSourceTransactionManager

doGetTransaction

isExistingTransaction

doBegin

doCommit

doSuspend

doRollback

doCleanupAfterCompletion

DataSourceUtils

ConnectionSynchronization

suspend

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