spring 声明式事务源码解析 PROPAGATION_REQUIRES

Posted 2020-12-19 会游泳的小猪

 当执行到47行的时候，会开启一个事务，此事务叫最新事务（老大事务），然后执行到51行的时候，老大事务会传播给51行的

userService，具体如何实现，请看我分析：

动态代理调用目标方法：

 一直进去会走进 

invokeWithinTransaction 方法，如下图：

 

 重点分析 

TransactionInfo txInfo = createTransactionIfNecessary(ptm, txAttr, joinpointIdentification);

如果有 必要就创建事务

 

 分析得到事务状态对象：status = tm.getTransaction(txAttr);

 

 如果是第一个service会走到  

if (isExistingTransaction(transaction)) 为假，就跳过走到下面的代码，开始事务，为最新事务（老大事务），开启事务的同事，会创立一个新的连接，connection
，然后把connection封装到connectionHolder里面，然后把此connnectionHolder放入 threadLocal里面，设置此老大事务为激活状态，并且设置事务状态newTransactin
为true，表示是老大事务。然后运行目标方法，目标方法里面由于 又有另外一个userService, 还是会进入事务的代理代码，会到

if (isExistingTransaction(transaction)) 此时这参数transactin是之前从threadLoacl里面拿到的事务，是之前老大事务留下来的一些属性，所以会任务此时是会存在的，
也就是我们认为的如果当前有事务，就用当前事务，就会进入if条件，走进去

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 {
         return startTransaction(definition, transaction, debugEnabled, suspendedResources);
      }
      catch (RuntimeException | Error beginEx) {
         resumeAfterBeginException(transaction, suspendedResources, beginEx);
         throw beginEx;
      }
   }

   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.
         return startTransaction(definition, transaction, debugEnabled, null);
      }
   }

进入

 return startTransaction(definition, transaction, debugEnabled, suspendedResources);

 

 

进入 doBegin

 开启事务，最主要是把connectin自动提交关闭 即代码 

con.setAutoCommit(false);
走完事务代码，然后走目标方法userService，走完以后，由于userService用的事务不是老大事务，所以在执行完目标方法后，提交事务的时候，会判断
状态是不是老大事务，如果不是老大事务就跳过提交（commit）的代码，老大事务判断依据是 newTransaction==true，以及是不是激活状态。然后就会回到
itemService，这个service的目标代码走完以后，就会会到事务代码的提交事务操作，这个时候由于itemService是老大事务，就提交（conmmit）,如果在
执行目标方法的时候发生运行时异常，就会进入catch代码块，回滚操作.