处理回滚流程图

传播机制图

AbstractPlatformTransactionManager的processRollback处理回滚

unexpectedRollback这个一般是false，除非是设置rollback-only=true，才是true，表示是全局的回滚标记。首先会进行回滚前回调，然后判断是否设置了保存点，比如NESTED会设置，要先回滚到保存点。如果状态是新的事务，那就进行回滚，如果不是新的，就设置一个回滚标记，内部是设置连接持有器回滚标记。然后回滚完成回调，根据事务状态信息，完成后数据清除,和线程的私有资源解绑，重置连接自动提交，隔离级别，是否只读，释放连接，恢复挂起事务等

    	private void processRollback(DefaultTransactionStatus status, boolean unexpected) {
    		try {
    			boolean unexpectedRollback = unexpected;//意外的回滚
    
    			try {
    				triggerBeforeCompletion(status);//回滚完成前回调
    				//有保存点回滚到保存点
    				if (status.hasSavepoint()) {
    					if (status.isDebug()) {
    						logger.debug("Rolling back transaction to savepoint");
    					}
    					status.rollbackToHeldSavepoint();
    				}
    				else if (status.isNewTransaction()) {//当前状态是一个新事务
    					if (status.isDebug()) {
    						logger.debug("Initiating transaction rollback");
    					}
    					doRollback(status);//进行回滚
    				}
    				else {
    					// Participating in larger transaction
    					if (status.hasTransaction()) {
    						if (status.isLocalRollbackOnly() || isGlobalRollbackOnParticipationFailure()) {
    							if (status.isDebug()) {
    								logger.debug("Participating transaction failed - marking existing transaction as rollback-only");
    							}
    							doSetRollbackOnly(status);//设置连接要回滚标记，也就是全局回滚
    						}
    						else {
    							if (status.isDebug()) {
    								logger.debug("Participating transaction failed - letting transaction originator decide on rollback");
    							}
    						}
    					}
    					else {
    						logger.debug("Should roll back transaction but cannot - no transaction available");
    					}
    					// Unexpected rollback only matters here if we're asked to fail early
    					if (!isFailEarlyOnGlobalRollbackOnly()) {
    						unexpectedRollback = false;
    					}
    				}
    			}
    			catch (RuntimeException | Error ex) {
    				triggerAfterCompletion(status, TransactionSynchronization.STATUS_UNKNOWN);
    				throw ex;
    			}
    			//回滚完成后回调
    			triggerAfterCompletion(status, TransactionSynchronization.STATUS_ROLLED_BACK);
    
    			// Raise UnexpectedRollbackException if we had a global rollback-only marker
    			if (unexpectedRollback) {
    				throw new UnexpectedRollbackException(
    						"Transaction rolled back because it has been marked as rollback-only");
    			}
    		}
    		finally {//根据事务状态信息，完成后数据清除,和线程的私有资源解绑，重置连接自动提交，隔离级别，是否只读，释放连接，恢复挂起事务等
    			cleanupAfterCompletion(status);
    		}
    	}

AbstractTransactionStatus的rollbackToHeldSavepoint回滚到保存点

如果设置了保存点的话，会进行处理，回滚到保存点，内部就是调用JDBC的连接回滚，释放保存点，其实没做什么，空的，最后清除保存点：

    	public void rollbackToHeldSavepoint() throws TransactionException {
    		Object savepoint = getSavepoint();
    		if (savepoint == null) {
    			throw new TransactionUsageException(
    					"Cannot roll back to savepoint - no savepoint associated with current transaction");
    		}
    		getSavepointManager().rollbackToSavepoint(savepoint);//回滚到保存点
    		getSavepointManager().releaseSavepoint(savepoint);//释放保存点，其实啥都没做
    		setSavepoint(null);//清除保存点
    	}

JdbcTransactionObjectSupport的rollbackToSavepoint回滚到保存点

内部就是获取连接对象，然后调用rollback回滚到保存点，然后重置连接持有器的回滚标记为false。所以这里不会影响外层的提交，否则外层提交的时候发现有回滚标记，会进行回滚的，这个在讲提交的时候会说到。

    	@Override
    	public void rollbackToSavepoint(Object savepoint) throws TransactionException {
    		ConnectionHolder conHolder = getConnectionHolderForSavepoint();
    		try {
    			conHolder.getConnection().rollback((Savepoint) savepoint);//回滚到保存点
    			conHolder.resetRollbackOnly();//重置回滚标记,不需要回滚
    		}
    		catch (Throwable ex) {
    			throw new TransactionSystemException("Could not roll back to JDBC savepoint", ex);
    		}
    	}

重置回滚标记：

DataSourceTransactionManager的doRollback回滚

真正的回滚就是这里啦，也是获取到JDBC的连接，然后回滚。

    	@Override
    	protected 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();//jdbc的回滚
    		}
    		catch (SQLException ex) {
    			throw new TransactionSystemException("Could not roll back JDBC transaction", ex);
    		}
    	}

DataSourceTransactionManager的doSetRollbackOnly设置回滚标记

如果既没有保存点，又不是新的事务，如果可以设置全局的回滚标记的话，就会设置。

    	@Override
    	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();
    	}

DataSourceTransactionObject 的setRollbackOnly设置回滚标记

最终就是设置了连接持有器的回滚标记啦。

    		public void setRollbackOnly() {
    			getConnectionHolder().setRollbackOnly();
    		}

最后再进行cleanupAfterCompletion的清除处理，里面也涉及到很多东西，后面说。

好了，今天就到这里了，希望对学习理解有帮助，大神看见勿喷，仅为自己的学习理解，能力有限，请多包涵。