在Spring的事务处理中，通用的事务处理流程框架是由抽象事务管理器AbstractPlatformTransactionManager来提供，而具体的底层事务处理实现，由PlatformTransactionManager的具体实现类来实现，如 DataSourceTransactionManager 、JtaTransactionManager和 HibernateTransactionManager等。
一、抽象事务管理器AbstractPlatformTransactionManager获取事务
抽象事务管理器AbstractPlatformTransactionManager提供了创建事务的模板，这个模板会被具体的事务处理器所使用，抽象事务管理器根据事务属性配置和当前线程绑定信息对事务是否需要创建以及如何创建进行一些通用的处理，然后把事务创建的底层细节交给具体的事务处理器实现。抽象事务管理器创建事务的模板方法如下：
public final TransactionStatus getTransaction(TransactionDefinition definition) throws TransactionException {
//doGetTransaction()方法是抽象方法，具体的实现由具体的事务处理器提供
Object transaction = doGetTransaction();
boolean debugEnabled = logger.isDebugEnabled();
//如果没有配置事务属性，则使用默认的事务属性
if (definition == null) {
definition = new DefaultTransactionDefinition();
}
//检查当前线程是否存在事务
if (isExistingTransaction(transaction)) {
//处理已存在的事务
return handleExistingTransaction(definition, transaction, debugEnabled);
}
//检查事务属性中timeout超时属性设置是否合理
if (definition.getTimeout() < TransactionDefinition.TIMEOUT_DEFAULT) {
throw new InvalidTimeoutException("Invalid transaction timeout", definition.getTimeout());
}
//对事务属性中配置的事务传播特性处理
//如果事务传播特性配置的是mandatory，当前没有事务存在，抛出异常
if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_MANDATORY) {
throw new IllegalTransactionStateException(
"No existing transaction found for transaction marked with propagation 'mandatory'");
}
//如果事务传播特性为required、required_new或nested
else if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRED ||
definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRES_NEW ||
definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NESTED) {
SuspendedResourcesHolder suspendedResources = suspend(null);
if (debugEnabled) {
logger.debug("Creating new transaction with name [" + definition.getName() + "]: " + definition);
}
//创建事务
try {
//不激活和当前线程绑定的事务，因为事务传播特性配置要求创建新的事务
boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
//创建一个新的事务状态
DefaultTransactionStatus status = newTransactionStatus(
definition, transaction, true, newSynchronization, debugEnabled, suspendedResources);
//创建事务的调用，具体实现由具体的事务处理器提供
doBegin(transaction, definition);
//初始化和同步事务状态
prepareSynchronization(status, definition);
return status;
}
catch (RuntimeException ex) {
resume(null, suspendedResources);
throw ex;
}
catch (Error err) {
resume(null, suspendedResources);
throw err;
}
}
else {
//创建空事务，针对supported类型的事务传播特性，激活和当前线程绑定的事务
boolean newSynchronization = (getTransactionSynchronization() == SYNCHRONIZATION_ALWAYS);
//准备事务状态
return prepareTransactionStatus(definition, null, true, newSynchronization, debugEnabled, null);
}
}
//准备事务状态
protected final DefaultTransactionStatus prepareTransactionStatus(
TransactionDefinition definition, Object transaction, boolean newTransaction,
boolean newSynchronization, boolean debug, Object suspendedResources) {
//创建事务状态
DefaultTransactionStatus status = newTransactionStatus(
definition, transaction, newTransaction, newSynchronization, debug, suspendedResources);
//准备事务状态
prepareSynchronization(status, definition);
return status;
}
//创建事务状态
protected DefaultTransactionStatus newTransactionStatus(
TransactionDefinition definition, Object transaction, boolean newTransaction,
boolean newSynchronization, boolean debug, Object suspendedResources) {
//判断是否是新事务，如果是新事务，则需要把事务属性存放到当前线程中
boolean actualNewSynchronization = newSynchronization &&
!TransactionSynchronizationManager.isSynchronizationActive();
return new DefaultTransactionStatus(
transaction, newTransaction, actualNewSynchronization,
definition.isReadOnly(), debug, suspendedResources);
}
//初始化事务属性
protected void prepareSynchronization(DefaultTransactionStatus status, TransactionDefinition definition) {
if (status.isNewSynchronization()) {
//设置当前是否有活跃事务 TransactionSynchronizationManager.setActualTransactionActive(status.hasTransaction());
//设置当前事务隔离级别 TransactionSynchronizationManager.setCurrentTransactionIsolationLevel(
(definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT) ?
definition.getIsolationLevel() : null);
TransactionSynchronizationManager.setCurrentTransactionReadOnly(definition.isReadOnly());
//设置当前事务名称 TransactionSynchronizationManager.setCurrentTransactionName(definition.getName());
TransactionSynchronizationManager.initSynchronization();
}
}
通过对上面创建事务对象的源码分析，我们看到这抽象事务管理器获取事务对象的这个模板方法主要功能是处理事务属性中配置的事务传播特性，对于判断是否存在事务的isExistingTransaction方法和创建事务对象的doBegin方法，均委派给具体的事务处理器实现。
二、抽象事务管理器AbstractPlatformTransactionManager处理已存在的事务
对于新事务的处理相对比较简单，只需根据事务属性配置创建，同时将事务隔离级别等属性保存到事务绑定的线程资源中。而对于已存在的事务处理相对比较复杂一些，在抽象事务管理器AbstractPlatformTransactionManager中通过handleExistingTransaction方法来处理已存在的事务：
private TransactionStatus handleExistingTransaction(
TransactionDefinition definition, Object transaction, boolean debugEnabled)
throws TransactionException {
//如果事务传播特性为：never，则抛出异常
if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NEVER) {
throw new IllegalTransactionStateException(
"Existing transaction found for transaction marked with propagation 'never'");
}
//如果事务传播特性是not_supported，同时当前线程存在事务，则将事务挂起
if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NOT_SUPPORTED) {
if (debugEnabled) {
logger.debug("Suspending current transaction");
}
//挂起事务
Object suspendedResources = suspend(transaction);
boolean newSynchronization = (getTransactionSynchronization() == SYNCHRONIZATION_ALWAYS);
//创建非事务的事务状态，让方法非事务地执行
return prepareTransactionStatus(
definition, null, false, newSynchronization, debugEnabled, suspendedResources);
}
//如果事务传播特性是required_new，则创建新事务，同时把当前线程中存在的
//事务挂起
if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRES_NEW) {
if (debugEnabled) {
logger.debug("Suspending current transaction, creating new transaction with name [" +
definition.getName() + "]");
}
//挂起已存在的事务
SuspendedResourcesHolder suspendedResources = suspend(transaction);
try {
boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
//将挂起的事务状态保存起来
DefaultTransactionStatus status = newTransactionStatus(
definition, transaction, true, newSynchronization, debugEnabled, suspendedResources);
//创建新事务
doBegin(transaction, definition);
prepareSynchronization(status, definition);
return status;
}
catch (RuntimeException beginEx) {
resumeAfterBeginException(transaction, suspendedResources, beginEx);
throw beginEx;
}
catch (Error beginErr) {
resumeAfterBeginException(transaction, suspendedResources, beginErr);
throw beginErr;
}
}
//如果事务传播特性是nested嵌套事务
if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NESTED) {
//如果不允许事务嵌套，则抛出异常
if (!isNestedTransactionAllowed()) {
throw new NestedTransactionNotSupportedException(
"Transaction manager does not allow nested transactions by default - " +
"specify 'nestedTransactionAllowed' property with value 'true'");
}
if (debugEnabled) {
logger.debug("Creating nested transaction with name [" + definition.getName() + "]");
}
//如果允许使用savepoint保存点保存嵌套事务
if (useSavepointForNestedTransaction()) {
//为当前事务创建一个保存点
DefaultTransactionStatus status =
prepareTransactionStatus(definition, transaction, false, false, debugEnabled, null);
status.createAndHoldSavepoint();
return status;
}
//如果不允许使用savepoint保存点保存嵌套事务
else {
//使用JTA的嵌套commit/rollback调用
boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
DefaultTransactionStatus status = newTransactionStatus(
definition, transaction, true, newSynchronization, debugEnabled, null);
doBegin(transaction, definition);
prepareSynchronization(status, definition);
return status;
}
}
//对于事务传播特性为supported和required的处理
if (debugEnabled) {
logger.debug("Participating in existing transaction");
}
//校验已存在的事务，如果已有事务与事务属性配置不一致，则抛出异常
if (isValidateExistingTransaction()) {
//如果事务隔离级别不是默认隔离级别
if (definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT) {
//获取当前事务的隔离级别
Integer currentIsolationLevel = TransactionSynchronizationManager.getCurrentTransactionIsolationLevel();
//如果获取到的当前事务隔离级别为null获取不等于事务属性配置的隔离级别
if (currentIsolationLevel == null || currentIsolationLevel != definition.getIsolationLevel()) {
Constants isoConstants = DefaultTransactionDefinition.constants;
throw new IllegalTransactionStateException("Participating transaction with definition [" + definition + "] specifies isolation level which is incompatible with existing transaction: " + (currentIsolationLevel != null ? isoConstants.toCode(currentIsolationLevel, DefaultTransactionDefinition.PREFIX_ISOLATION) : "(unknown)"));
}
}
//如果事务不是只读
if (!definition.isReadOnly()) {
//如果当前已有事务是只读
if (TransactionSynchronizationManager.isCurrentTransactionReadOnly()) {
throw new IllegalTransactionStateException("Participating transaction with definition [" +
definition + "] is not marked as read-only but existing transaction is");
}
}
}
boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
//返回当前事务的执行状态
return prepareTransactionStatus(definition, transaction, false, newSynchronization, debugEnabled, null);
}
三、DataSourceTransactionManager事务处理器的实现
DataSourceTransactionManager数据源事务处理器是针对JDBC连接提供的事务处理器实现，即数据源事务处理器把数据库Connection连接和当前线程进行绑定，通过直接调用数据库连接Connection的提交和回滚方法实现事务的提供和回滚处理。其源码如下：
public class DataSourceTransactionManager extends AbstractPlatformTransactionManager
implements ResourceTransactionManager, InitializingBean {
//注入数据源
private DataSource dataSource;
//数据源事务处理器默认构造方法，创建一个数据源事务处理器实例，并设置允许嵌套事务
public DataSourceTransactionManager() {
setNestedTransactionAllowed(true);
}
//根据给定数据源，创建一个数据源事务处理器实例
public DataSourceTransactionManager(DataSource dataSource) {
this();
setDataSource(dataSource);
afterPropertiesSet();
}
//设置数据源
public void setDataSource(DataSource dataSource) {
if (dataSource instanceof TransactionAwareDataSourceProxy) {
//如果数据源是一个事务包装数据源代理，则获取事务包装代理的目标数据源
this.dataSource = ((TransactionAwareDataSourceProxy) dataSource).getTargetDataSource();
}
else {
this.dataSource = dataSource;
}
}
//获取数据源
public DataSource getDataSource() {
return this.dataSource;
}
//数据源事务处理器对象构造方法的回调函数
public void afterPropertiesSet() {
if (getDataSource() == null) {
throw new IllegalArgumentException("Property 'dataSource' is required");
}
}
public Object getResourceFactory() {
return getDataSource();
}
//创建事务，对数据库而言，是由Connection来完成事务工作的。该方法把数据库的//Connection对象放到一个ConnectionHolder对象中，然后封装到一个
//DataSourceTransactionObject对象中
protected Object doGetTransaction() {
//创建数据源事务对象
DataSourceTransactionObject txObject = new DataSourceTransactionObject();
//设置数据源事务对象对嵌套事务使用保存点
txObject.setSavepointAllowed(isNestedTransactionAllowed());
//从事务管理容器中获取存放数据库Connection的对象
ConnectionHolder conHolder =
(ConnectionHolder) TransactionSynchronizationManager.getResource(this.dataSource);
txObject.setConnectionHolder(conHolder, false);
return txObject;
}
//判断是否已经存在事务
protected boolean isExistingTransaction(Object transaction) {
DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;
//根据存放数据库连接的ConnectionHolder的isTransactionActive属性来判断
return (txObject.getConnectionHolder() != null && txObject.getConnectionHolder().isTransactionActive());
}
//处理事务开始的方法
protected void doBegin(Object transaction, TransactionDefinition definition) {
DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;
Connection con = null;
try {
//如果数据源事务对象的ConnectionHolder为null或者是事务同步的
if (txObject.getConnectionHolder() == null ||
txObject.getConnectionHolder().isSynchronizedWithTransaction()) {
//获取当前数据源的数据库连接
Connection newCon = this.dataSource.getConnection();
if (logger.isDebugEnabled()) {
logger.debug("Acquired Connection [" + newCon + "] for JDBC transaction");
}
//为数据源事务对象设置ConnectionHolder
txObject.setConnectionHolder(new ConnectionHolder(newCon), true);
}
//设置数据源事务对象的事务同步 txObject.getConnectionHolder().setSynchronizedWithTransaction(true);
//获取数据源事务对象的数据库连接
con = txObject.getConnectionHolder().getConnection();
//根据数据连接和事务属性，获取数据库连接的事务隔离级别
Integer previousIsolationLevel = DataSourceUtils.prepareConnectionForTransaction(con, definition);
//为数据源事务对象设置事务隔离级别
txObject.setPreviousIsolationLevel(previousIsolationLevel);
//如果数据库连接设置了自动事务提交属性，则关闭自动提交
if (con.getAutoCommit()) {
//保存数据库连接设置的自动连接到数据源事务对象中
txObject.setMustRestoreAutoCommit(true);
if (logger.isDebugEnabled()) {
logger.debug("Switching JDBC Connection [" + con + "] to manual commit");
}
//设置数据库连接自动事务提交属性为false，即禁止自动事务提交
con.setAutoCommit(false);
}
//激活当前数据源事务对象的事务配置
txObject.getConnectionHolder().setTransactionActive(true);
//获取事务配置的超时时长
int timeout = determineTimeout(definition);
//如果事务配置的超时时长不等于事务的默认超时时长
if (timeout != TransactionDefinition.TIMEOUT_DEFAULT) {
//数据源事务对象设置超时时长
txObject.getConnectionHolder().setTimeoutInSeconds(timeout);
}
//把当前数据库Connection和线程绑定
if (txObject.isNewConnectionHolder()) {
TransactionSynchronizationManager.bindResource(getDataSource(), txObject.getConnectionHolder());
}
}
catch (Exception ex) {
DataSourceUtils.releaseConnection(con, this.dataSource);
throw new CannotCreateTransactionException("Could not open JDBC Connection for transaction", ex);
}
}
//事务挂起
protected Object doSuspend(Object transaction) {
//获取事务对象
DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;
//将事务对象中的ConnectionHolders设置为null
txObject.setConnectionHolder(null);
ConnectionHolder conHolder = (ConnectionHolder)
//解除事务对象和当前线程的绑定 TransactionSynchronizationManager.unbindResource(this.dataSource);
return conHolder;
}
//事务恢复
protected void doResume(Object transaction, Object suspendedResources) {
//获取已暂停事务的ConnectionHolder
ConnectionHolder conHolder = (ConnectionHolder) suspendedResources;
//重新将事务对象和当前线程绑定
TransactionSynchronizationManager.bindResource(this.dataSource, conHolder);
}
//事务提交
protected void doCommit(DefaultTransactionStatus status) {
//获取事务对象
DataSourceTransactionObject txObject = (DataSourceTransactionObject) status.getTransaction();
//通过事务对象获取数据库连接
Connection con = txObject.getConnectionHolder().getConnection();
if (status.isDebug()) {
logger.debug("Committing JDBC transaction on Connection [" + con + "]");
}
try {
//使用数据库连接手动进行事务提交
con.commit();
}
catch (SQLException ex) {
throw new TransactionSystemException("Could not commit JDBC transaction", ex);
}
}
//事务回滚
protected void doRollback(DefaultTransactionStatus status) {
//获取事务对象
DataSourceTransactionObject txObject = (DataSourceTransactionObject) status.getTransaction();
//通过事务对象获取数据库连接
Connection con = txObject.getConnectionHolder().getConnection();
if (status.isDebug()) {
logger.debug("Rolling back JDBC transaction on Connection [" + con + "]");
}
try {
//通过调用数据库连接的回滚方法完成事务回滚操作
con.rollback();
}
catch (SQLException ex) {
throw new TransactionSystemException("Could not roll back JDBC transaction", ex);
}
}
//设置回滚
protected void doSetRollbackOnly(DefaultTransactionStatus status) {
DataSourceTransactionObject txObject = (DataSourceTransactionObject) status.getTransaction();
if (status.isDebug()) {
logger.debug("Setting JDBC transaction [" + txObject.getConnectionHolder().getConnection() +
"] rollback-only");
}
txObject.setRollbackOnly();
}
//操作完成之后清除操作
protected void doCleanupAfterCompletion(Object transaction) {
DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;
//移除当前线程绑定的ConnectionHolder
if (txObject.isNewConnectionHolder()) {
TransactionSynchronizationManager.unbindResource(this.dataSource);
}
Connection con = txObject.getConnectionHolder().getConnection();
try {
//如果事务对象保存了自动事务提交属性，则设置数据库连接的自动事务提交属性
if (txObject.isMustRestoreAutoCommit()) {
con.setAutoCommit(true);
}
//事务结束后重置数据库连接
DataSourceUtils.resetConnectionAfterTransaction(con, txObject.getPreviousIsolationLevel());
}
catch (Throwable ex) {
logger.debug("Could not reset JDBC Connection after transaction", ex);
}
//如果事务对象中有新的ConnectionHolder
if (txObject.isNewConnectionHolder()) {
if (logger.isDebugEnabled()) {
logger.debug("Releasing JDBC Connection [" + con + "] after transaction");
}
//释放数据库连接
DataSourceUtils.releaseConnection(con, this.dataSource);
}
//清除事务对象的ConnectionHolder
txObject.getConnectionHolder().clear();
}
//数据源事务对象，内部类
private static class DataSourceTransactionObject extends JdbcTransactionObjectSupport {
//是否有新的ConnectionHolder
private boolean newConnectionHolder;
//是否保存自动提交
private boolean mustRestoreAutoCommit;
//设置ConnectionHolder
public void setConnectionHolder(ConnectionHolder connectionHolder, boolean newConnectionHolder) {
//为父类JdbcTransactionObjectSupport设置ConnectionHolder
super.setConnectionHolder(connectionHolder);
this.newConnectionHolder = newConnectionHolder;
}
public boolean isNewConnectionHolder() {
return this.newConnectionHolder;
}
//调用父类JdbcTransactionObjectSupport的相关方法，查询收费存在事务
public boolean hasTransaction() {
return (getConnectionHolder() != null && getConnectionHolder().isTransactionActive());
}
//设置是否保存自动提交
public void setMustRestoreAutoCommit(boolean mustRestoreAutoCommit) {
this.mustRestoreAutoCommit = mustRestoreAutoCommit;
}
public boolean isMustRestoreAutoCommit() {
return this.mustRestoreAutoCommit;
}
//设置数据库连接在操作失败是，是否只回滚处理
public void setRollbackOnly() {
getConnectionHolder().setRollbackOnly();
}
public boolean isRollbackOnly() {
return getConnectionHolder().isRollbackOnly();
}
}
}
通过上述对数据源事务处理器的源码分析，我们看到，事务的提交、回滚等操作是通过直接调用数据库连接Connection的提交和回滚方法实现的，由于自动事务提交对应用程序性能影响很大，因此在进行事务提交时，我们首先禁止数据库连接的自动事务提交，事务提供操作通过手动实现。
四、HibernateTransactionManager事务处理器的实现
相对于数据源的事务处理器来说，Hibernate的事务处理器相对要复杂一些，它是通过对Hibernate的会话Session的管理来完成事务处理实现的。Hibernate事务处理器的事务处理相关源码如下：
public class HibernateTransactionManager extends AbstractPlatformTransactionManager
implements ResourceTransactionManager, BeanFactoryAware, InitializingBean {
……
//获取Hibernate事务
protected Object doGetTransaction() {
//创建Hibernate事务对象
HibernateTransactionObject txObject = new HibernateTransactionObject();
//根据是否允许嵌套事务设置事务对象是否允许保存点
txObject.setSavepointAllowed(isNestedTransactionAllowed());
//从线程中获取SessionHolder,SessionHolder是在事务开始时与线程绑定的。
SessionHolder sessionHolder =
(SessionHolder) TransactionSynchronizationManager.getResource(getSessionFactory());
//如果获取到的SessionHolder不为null
if (sessionHolder != null) {
if (logger.isDebugEnabled()) {
logger.debug("Found thread-bound Session [" +
SessionFactoryUtils.toString(sessionHolder.getSession()) + "] for Hibernate transaction");
}
//把获取到的SessionHolder设置到Hibernate事务对象中
txObject.setSessionHolder(sessionHolder);
}
//如果当前Hibernate事务处理器有被管理的Hibernate Session
else if (this.hibernateManagedSession) {
try {
//获取当前的Hibernate Session
Session session = getSessionFactory().getCurrentSession();
if (logger.isDebugEnabled()) {
logger.debug("Found Hibernate-managed Session [" +
SessionFactoryUtils.toString(session) + "] for Spring-managed transaction");
}
//设置Hibernate事务对象已经存在指定的Session
txObject.setExistingSession(session);
}
catch (HibernateException ex) {
throw new DataAccessResourceFailureException(
"Could not obtain Hibernate-managed Session for Spring-managed transaction", ex);
}
}
//如果获取到的数据源不为null
if (getDataSource() != null) {
//将获取到的数据源和当前线程绑定
ConnectionHolder conHolder = (ConnectionHolder)
TransactionSynchronizationManager.getResource(getDataSource());
txObject.setConnectionHolder(conHolder);
}
return txObject;
}
//是否已存在事务
protected boolean isExistingTransaction(Object transaction) {
HibernateTransactionObject txObject = (HibernateTransactionObject) transaction;
//根据事务对象是否存在Spring管理的事务，或者通过判断是否存在Hibernate //Session或者事务对象中有被Hibernate管理的事务
return (txObject.hasSpringManagedTransaction() ||
(this.hibernateManagedSession && txObject.hasHibernateManagedTransaction()));
}
//处理事务开始
protected void doBegin(Object transaction, TransactionDefinition definition) {
//获取事务对象
HibernateTransactionObject txObject = (HibernateTransactionObject) transaction;
//如果事务对象有ConnectionHolder，且事务对象的数据库连接不是事务同步的
if (txObject.hasConnectionHolder() && !txObject.getConnectionHolder().isSynchronizedWithTransaction()) {
throw new IllegalTransactionStateException(
"Pre-bound JDBC Connection found! HibernateTransactionManager does not support " +
"running within DataSourceTransactionManager if told to manage the DataSource itself. " +
"It is recommended to use a single HibernateTransactionManager for all transactions " +
"on a single DataSource, no matter whether Hibernate or JDBC access.");
}
Session session = null;
try {
//如果事务对象的SessionHolder为null，或者事务对象Hibernate
//Session是事务同步的
if (txObject.getSessionHolder() == null || txObject.getSessionHolder().isSynchronizedWithTransaction()) {
//获取Hibernate事务处理器中的实体拦截器
Interceptor entityInterceptor = getEntityInterceptor();
//获取Hibernate Session，如果实体拦截器不为null，则打开指定
//实体拦截器的Session，如果实体拦截器为null，则打开新Session
Session newSession = (entityInterceptor != null ?
getSessionFactory().openSession(entityInterceptor) : getSessionFactory().openSession());
if (logger.isDebugEnabled()) {
logger.debug("Opened new Session [" + SessionFactoryUtils.toString(newSession) +
"] for Hibernate transaction");
}
//将获取的Hibernate Session设置到事务对象中
txObject.setSession(newSession);
}
//如果Hibernate事务处理器中的SessionHolder不为null，则
//获取SessionHolder中已有的Hibernate Session
session = txObject.getSessionHolder().getSession();
//允许为JDBC连接改变事务设置
if (this.prepareConnection && isSameConnectionForEntireSession(session)) {
if (logger.isDebugEnabled()) {
logger.debug(
"Preparing JDBC Connection of Hibernate Session [" + SessionFactoryUtils.toString(session) + "]");
}
//获取Session连接
Connection con = session.connection();
//获取事务的隔离级别
Integer previousIsolationLevel = DataSourceUtils.prepareConnectionForTransaction(con, definition);
//设置事务对象的事务隔离级别 txObject.setPreviousIsolationLevel(previousIsolationLevel);
}
//不允许为JDBC连接改成事务设置
else {
//如果事务隔离级别不是默认事务隔离级别
if (definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT) {
throw new InvalidIsolationLevelException(
"HibernateTransactionManager is not allowed to support custom isolation levels: " +
"make sure that its 'prepareConnection' flag is on (the default) and that the " +
"Hibernate connection release mode is set to 'on_close' (SpringTransactionFactory's default). " +
"Make sure that your LocalSessionFactoryBean actually uses SpringTransactionFactory: Your " +
"Hibernate properties should *not* include a 'hibernate.transaction.factory_class' property!");
}
if (logger.isDebugEnabled()) {
logger.debug(
"Not preparing JDBC Connection of Hibernate Session [" + SessionFactoryUtils.toString(session) + "]");
}
}
//如果事务是只读，且事务对象是新的Hibernate Session
if (definition.isReadOnly() && txObject.isNewSession()) {
//设置Hibernate Session刷新模式为手动
session.setFlushMode(FlushMode.MANUAL);
}
//如果事务是非只读的，且事务对象不是新Hibernate Session
if (!definition.isReadOnly() && !txObject.isNewSession()) {
//或者Hibernate的刷新模式
FlushMode flushMode = session.getFlushMode();
//设置Session的刷新模式
if (flushMode.lessThan(FlushMode.COMMIT)) {
session.setFlushMode(FlushMode.AUTO);
//为事务对象设置刷新模式 txObject.getSessionHolder().setPreviousFlushMode(flushMode);
}
}
Transaction hibTx;
//获取事务超时时长
int timeout = determineTimeout(definition);
//如果事务配置的超时时长不是事务默认超时时长
if (timeout != TransactionDefinition.TIMEOUT_DEFAULT) {
//获取Hibernate Session事务
hibTx = session.getTransaction();
//为事务对象设置超时时长
hibTx.setTimeout(timeout);
//开启事务
hibTx.begin();
}
//如果事务配置的超时时长是默认超时时长
else {
//通过Hibernate Session直接开启事务
hibTx = session.beginTransaction();
}
//把事务设置到事务对象的SessionHolder中，并且线程绑定
txObject.getSessionHolder().setTransaction(hibTx);
//如果数据源不为null，即设置了数据源
if (getDataSource() != null) {
//使用Hibernate Session打开数据库连接
Connection con = session.connection();
//创建ConnectionHolder
ConnectionHolder conHolder = new ConnectionHolder(con);
//设置超时时长
if (timeout != TransactionDefinition.TIMEOUT_DEFAULT) {
conHolder.setTimeoutInSeconds(timeout);
}
if (logger.isDebugEnabled()) {
logger.debug("Exposing Hibernate transaction as JDBC transaction [" + con + "]");
}
//将数据源和JDBC ConnectionHolder绑定到当前线程 TransactionSynchronizationManager.bindResource(getDataSource(), conHolder);
//将创建的JDBC ConnectionHolder设置到事务对象中
txObject.setConnectionHolder(conHolder);
}
//如果事务对象中的SessionHolder是新的
if (txObject.isNewSessionHolder()) {
//当SessionHolder和当前线程绑定起来 TransactionSynchronizationManager.bindResource(getSessionFactory(), txObject.getSessionHolder());
}
//设置事务对象中的SessionHolder是事务同步的 txObject.getSessionHolder().setSynchronizedWithTransaction(true);
}
//事务开启过程中异常处理
catch (Exception ex) {
if (txObject.isNewSession()) {
try {
//如果Session的事务上激活的，回滚Session的事务
if (session.getTransaction().isActive()) {
session.getTransaction().rollback();
}
}
catch (Throwable ex2) {
logger.debug("Could not rollback Session after failed transaction begin", ex);
}
finally {
//关闭Session
SessionFactoryUtils.closeSession(session);
}
}
throw new CannotCreateTransactionException("Could not open Hibernate Session for transaction", ex);
}
}
//事务挂起
protected Object doSuspend(Object transaction) {
HibernateTransactionObject txObject = (HibernateTransactionObject) transaction;
//把当前的SessionHolder从线程中和事务对象中释放
txObject.setSessionHolder(null);
//解析SessionHolder和线程的绑定
SessionHolder sessionHolder =
(SessionHolder) TransactionSynchronizationManager.unbindResource(getSessionFactory());
txObject.setConnectionHolder(null);
ConnectionHolder connectionHolder = null;
//解除数据源和线程的绑定
if (getDataSource() != null) {
connectionHolder = (ConnectionHolder) TransactionSynchronizationManager.unbindResource(getDataSource());
}
return new SuspendedResourcesHolder(sessionHolder, connectionHolder);
}
//事务恢复
protected void doResume(Object transaction, Object suspendedResources) {
SuspendedResourcesHolder resourcesHolder = (SuspendedResourcesHolder) suspendedResources;
//如果事务管理器中有SessionFactory
if (TransactionSynchronizationManager.hasResource(getSessionFactory())) {
//解除SessionFactory和当前线程的绑定
TransactionSynchronizationManager.unbindResource(getSessionFactory());
}
//如果事务管理器中没有SessionFactory，则将Session和当前线程绑定 TransactionSynchronizationManager.bindResource(getSessionFactory(), resourcesHolder.getSessionHolder());
if (getDataSource() != null) {
TransactionSynchronizationManager.bindResource(getDataSource(), resourcesHolder.getConnectionHolder());
}
}
//准备提交
protected void prepareForCommit(DefaultTransactionStatus status) {
//如果事务配置为FlushBeforeCommit，并且是新事务
if (this.earlyFlushBeforeCommit && status.isNewTransaction()) {
//获取事务对象
HibernateTransactionObject txObject = (HibernateTransactionObject) status.getTransaction();
//回去事务对象中的Session
Session session = txObject.getSessionHolder().getSession();
//如果Session的刷新模式不低于COMMIT
if (!session.getFlushMode().lessThan(FlushMode.COMMIT)) {
logger.debug("Performing an early flush for Hibernate transaction");
try {
//刷新Session
session.flush();
}
catch (HibernateException ex) {
throw convertHibernateAccessException(ex);
}
finally {
//把Session的刷新模式设置为MANUAL
session.setFlushMode(FlushMode.MANUAL);
}
}
}
}
//提交处理
protected void doCommit(DefaultTransactionStatus status) {
//获取当前的Hibernate事务对象
HibernateTransactionObject txObject = (HibernateTransactionObject) status.getTransaction();
if (status.isDebug()) {
logger.debug("Committing Hibernate transaction on Session [" +SessionFactoryUtils.toString(txObject.getSessionHolder().getSession()) + "]");
}
try {
//通过Hibernate事务完成提交
txObject.getSessionHolder().getTransaction().commit();
}
catch (org.hibernate.TransactionException ex) {
throw new TransactionSystemException("Could not commit Hibernate transaction", ex);
}
catch (HibernateException ex) {
throw convertHibernateAccessException(ex);
}
}
//回滚处理
protected void doRollback(DefaultTransactionStatus status) {
//获取Hibernate事务对象
HibernateTransactionObject txObject = (HibernateTransactionObject) status.getTransaction();
if (status.isDebug()) {
logger.debug("Rolling back Hibernate transaction on Session ["+SessionFactoryUtils.toString(txObject.getSessionHolder().getSession()) + "]");
}
try {
//通过Hibernate事务执行回滚操作
txObject.getSessionHolder().getTransaction().rollback();
}
catch (org.hibernate.TransactionException ex) {
throw new TransactionSystemException("Could not roll back Hibernate transaction", ex);
}
catch (HibernateException ex) {
throw convertHibernateAccessException(ex);
}
finally {
if (!txObject.isNewSession() && !this.hibernateManagedSession) {
//清除事务对象中的Hibernate Session
txObject.getSessionHolder().getSession().clear();
}
}
}
……
}
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