由于springAop的实现思路，在业务代码执行的时候，会将所有的通知转换为拦截器链，所会依次执行拦截器的invoke方法，在spring事物中TransactionInterceptor构成了spring事物的核心。
代码如下：
@Override public Object invoke(final MethodInvocation invocation) throws Throwable { // Work out the target class: may be {@code null}. // The TransactionAttributeSource should be passed the target class // as well as the method, which may be from an interface. Class<?> targetClass = (invocation.getThis() != null ? AopUtils.getTargetClass(invocation.getThis()) : null); // Adapt to TransactionAspectSupport's invokeWithinTransaction... // 执行业务代码的部分 return invokeWithinTransaction(invocation.getMethod(), targetClass, new InvocationCallback() { @Override public Object proceedWithInvocation() throws Throwable { // 执行下一个拦截器 return invocation.proceed(); } }); }
进入代码进行分析：
protected Object invokeWithinTransaction(Method method, Class<?> targetClass, final InvocationCallback invocation) throws Throwable { // If the transaction attribute is null, the method is non-transactional. final TransactionAttribute txAttr = getTransactionAttributeSource().getTransactionAttribute(method, targetClass); final PlatformTransactionManager tm = determineTransactionManager(txAttr); final String joinpointIdentification = methodIdentification(method, targetClass); // 声明式事物处理 if (txAttr == null || !(tm instanceof CallbackPreferringPlatformTransactionManager)) { // Standard transaction demarcation with getTransaction and commit/rollback calls. // 创建TransactionInfo TransactionInfo txInfo = createTransactionIfNecessary(tm, txAttr, joinpointIdentification); Object retVal = null; try { // This is an around advice: Invoke the next interceptor in the chain. // This will normally result in a target object being invoked. // 执行目标业务方法 retVal = invocation.proceedWithInvocation(); } catch (Throwable ex) { // target invocation exception // 遇到异常进行回滚 completeTransactionAfterThrowing(txInfo, ex); throw ex; } finally { // 清除信息 cleanupTransactionInfo(txInfo); } // 提价事物 commitTransactionAfterReturning(txInfo); return retVal; } else { //编程式事物处理 // It's a CallbackPreferringPlatformTransactionManager: pass a TransactionCallback in. try { Object result = ((CallbackPreferringPlatformTransactionManager) tm).execute(txAttr, new TransactionCallback<Object>() { @Override public Object doInTransaction(TransactionStatus status) { TransactionInfo txInfo = prepareTransactionInfo(tm, txAttr, joinpointIdentification, status); try { return invocation.proceedWithInvocation(); } catch (Throwable ex) { if (txAttr.rollbackOn(ex)) { // A RuntimeException: will lead to a rollback. if (ex instanceof RuntimeException) { throw (RuntimeException) ex; } else { throw new ThrowableHolderException(ex); } } else { // A normal return value: will lead to a commit. return new ThrowableHolder(ex); } } finally { cleanupTransactionInfo(txInfo); } } }); // Check result: It might indicate a Throwable to rethrow. if (result instanceof ThrowableHolder) { throw ((ThrowableHolder) result).getThrowable(); } else { return result; } } catch (ThrowableHolderException ex) { throw ex.getCause(); } } }
继续进入创建TransactionInfo类的代码中进行分析：
protected TransactionInfo createTransactionIfNecessary( PlatformTransactionManager tm, TransactionAttribute txAttr, final String joinpointIdentification) { // If no name specified, apply method identification as transaction name. if (txAttr != null && txAttr.getName() == null) { txAttr = new DelegatingTransactionAttribute(txAttr) { @Override public String getName() { return joinpointIdentification; } }; } TransactionStatus status = null; if (txAttr != null) { if (tm != null) { // 获取事物的TransactionStatus status = tm.getTransaction(txAttr); } else { if (logger.isDebugEnabled()) { logger.debug("Skipping transactional joinpoint [" + joinpointIdentification + "] because no transaction manager has been configured"); } } } //根据获取的TransactionStatus创建一个TransactionInfo对象并返回 return prepareTransactionInfo(tm, txAttr, joinpointIdentification, status); }
进一步分析获取事物TransactionStatus的代码：
public final TransactionStatus getTransaction(TransactionDefinition definition) throws TransactionException { Object transaction = doGetTransaction(); // Cache debug flag to avoid repeated checks. boolean debugEnabled = logger.isDebugEnabled(); if (definition == null) { // Use defaults if no transaction definition given. definition = new DefaultTransactionDefinition(); } if (isExistingTransaction(transaction)) { // Existing transaction found -> check propagation behavior to find out how to behave. // 处理已经存在的事物 return handleExistingTransaction(definition, transaction, debugEnabled); } // Check definition settings for new transaction. if (definition.getTimeout() < TransactionDefinition.TIMEOUT_DEFAULT) { throw new InvalidTimeoutException("Invalid transaction timeout", definition.getTimeout()); } // No existing transaction found -> check propagation behavior to find out how to proceed. if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_MANDATORY) { throw new IllegalTransactionStateException( "No existing transaction found for transaction marked with propagation 'mandatory'"); } 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); } try { boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER); DefaultTransactionStatus status = newTransactionStatus( definition, transaction, true, newSynchronization, debugEnabled, suspendedResources); doBegin(transaction, definition); prepareSynchronization(status, definition); return status; } catch (RuntimeException ex) { resume(null, suspendedResources); throw ex; } catch (Error err) { resume(null, suspendedResources); throw err; } } else { // Create "empty" transaction: no actual transaction, but potentially synchronization. if (definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT && logger.isWarnEnabled()) { logger.warn("Custom isolation level specified but no actual transaction initiated; " + "isolation level will effectively be ignored: " + definition); } boolean newSynchronization = (getTransactionSynchronization() == SYNCHRONIZATION_ALWAYS); return prepareTransactionStatus(definition, null, true, newSynchronization, debugEnabled, null); } }
spring处理已经存在事物的逻辑：
需要主要考虑两种情况：第一：如果当前事物的传播行为是PROPAGATION_REQUIRES_NEW ，则需要开启新的事物，不考虑原有的事物，此时，spring会将原有的事物挂起，待当前事物完成以后则将挂起的事物恢复，如果当前事物失败，不会引起挂起事物的回滚。第二：如果传播行为设置是,PROPAGATION_NESTED,则spring允许嵌套事物的存在，此时会设置一个保存点，嵌套事物的回滚会根据保存点进行回滚。但是由于JTA事物不支持保存点设置，如果是JTA事物设置允许嵌套事物，则会按照传播行为为PROPAGATION_REQUIRES_NEW的情况下面进行处理，即开启新的事物。
处理已经存在事物的源码：
private TransactionStatus handleExistingTransaction( TransactionDefinition definition, Object transaction, boolean debugEnabled) throws TransactionException { if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NEVER) { throw new IllegalTransactionStateException( "Existing transaction found for transaction marked with propagation 'never'"); } if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NOT_SUPPORTED) { if (debugEnabled) { logger.debug("Suspending current transaction"); } Object suspendedResources = suspend(transaction); boolean newSynchronization = (getTransactionSynchronization() == SYNCHRONIZATION_ALWAYS); return prepareTransactionStatus( definition, null, false, newSynchronization, debugEnabled, suspendedResources); } if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_REQUIRES_NEW) { if (debugEnabled) { logger.debug("Suspending current transaction, creating new transaction with name [" + definition.getName() + "]"); } SuspendedResourcesHolder suspendedResources = suspend(transaction); try { boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER); DefaultTransactionStatus status = newTransactionStatus( definition, transaction, true, newSynchronization, debugEnabled, suspendedResources); 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; } } if (definition.getPropagationBehavior() == TransactionDefinition.PROPAGATION_NESTED) { 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() + "]"); } if (useSavepointForNestedTransaction()) { // Create savepoint within existing Spring-managed transaction, // through the SavepointManager API implemented by TransactionStatus. // Usually uses JDBC 3.0 savepoints. Never activates Spring synchronization. DefaultTransactionStatus status = prepareTransactionStatus(definition, transaction, false, false, debugEnabled, null); status.createAndHoldSavepoint(); return status; } else { // Nested transaction through nested begin and commit/rollback calls. // Usually only for JTA: Spring synchronization might get activated here // in case of a pre-existing JTA transaction. boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER); DefaultTransactionStatus status = newTransactionStatus( definition, transaction, true, newSynchronization, debugEnabled, null); doBegin(transaction, definition); prepareSynchronization(status, definition); return status; } } // Assumably PROPAGATION_SUPPORTS or PROPAGATION_REQUIRED. if (debugEnabled) { logger.debug("Participating in existing transaction"); } if (isValidateExistingTransaction()) { if (definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT) { Integer currentIsolationLevel = TransactionSynchronizationManager.getCurrentTransactionIsolationLevel(); 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)")); } } if (!definition.isReadOnly()) { 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); return prepareTransactionStatus(definition, transaction, false, newSynchronization, debugEnabled, null); }