NCC 事务

2024-04-08 22:46:58

NC事务
1.NC中新建独立事务
NC中接口方法命名为method__RequiresNew(Object param) throws Exception ，后续步骤同新建NC组件一样——实现接口，在upm中注册接口。

public interface IGuanyiBillFilterService {

/**
* 更新已处理的单据记录
* @param records
*/
void updateBillRecord__RequiresNew(List<GuanYiErpBillRecord> records) throws DAOException;

代码中调用事务，需通过NCLocator进行远程组件调用事务才生效，直接调用不会新建事务。

2.NC事务原理
当进行远程组件调用时会使用动态代理执行目标方法，其中会判断方法名是否具有_RequiresNew后缀来决定是否新建事务

public class CMTEJBServiceHandler implements InvocationHandler {
　　　　　　...
		public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
			try {
				if (method.getName().endsWith("_RequiresNew")) {
					return this.cmtProxy.delegate_RequiresNew(this.wrapped, method, args);
				}
				return this.cmtProxy.delegate(this.wrapped, method, args);
			} catch (Throwable e) {
				Throwable lastEJBException = getLastEJBException(e);
				if (lastEJBException == null) {
					throw e;
				}
				if (lastEJBException.getCause() != null) {
					throw lastEJBException.getCause();
				}
				throw e;
			}
		}
　　　　　　　　...
	}

下一步会进入到如下方法，其中需要关注的是beforeCallMethod和afterCallMethod，其中分别新建和结束事务

 public class CMTProxy_Local
   extends BeanBase
   implements CMTProxyEjbObject
 {
  .....
   
   public Object delegate_RequiresNew(Object arg0, Method arg1, Object[] arg2)
     throws Exception
   {
     beforeCallMethod(200);
     try {
       o = _getBeanObject().delegate_RequiresNew(arg0, arg1, arg2);
     }
     catch (Exception e) {
       er = e;
     } catch (Throwable thr) {
       er = new FrameworkEJBException("Fatal unknown error", thr);
     }
     try {
       afterCallMethod(200, er);
     }
   .....
   }
   
 
   public Object delegate(Object arg0, Method arg1, Object[] arg2)
     throws Exception
   {
   ....
     beforeCallMethod(201);
     try {
       o = _getBeanObject().delegate_RequiresNew(arg0, arg1, arg2);
     }
     catch (Exception e) {
       er = e;
     } catch (Throwable thr) {
       er = new FrameworkEJBException("Fatal unknown error", thr);
     }
     try {
       afterCallMethod(201, er);
     }
    ......
   }
 }

让我们看看里面干了啥…

beforeCallMethod中首先判断组件是否是容器控制事务，获取事务类型和事务隔离级别后调用TransactionManager的begin方法

   protected void beforeCallMethod(int methodId)
   {
    ......
     boolean isCmt = ((HomeBase)getEJBLocalHome()).getEJBBeanDescriptor().isCmt();
     
     if (isCmt)
     {
       try
       {
         this.currentMethodTransectionType = getMethodTransectionType(methodId);
         int isolateLevel = getMethodIsolateLevelType(methodId);
         setIerpTransactionManagerProxy(TransactionFactory.getTMProxy());
         getIerpTransactionManagerProxy().begin(this.currentMethodTransectionType, isolateLevel);
       }
       catch (Exception e) {
         Logger.error("BeforeCallMethod", e);
       }
     }
     else {
       if (getIerpUserTransaction() == null) {
         setIerpTransactionManagerProxy(null);
         
         setIerpUserTransaction(TransactionFactory.getUTransaction());
       }
       
       getIerpUserTransaction().bindToCurrentThread();
     }
     
    ......
   }

UAPTransactionManager中的begin方法，其中3是对应声明了_RequiresNew的接口方法，1是对应普通接口方法，自己debug可以跟踪到。

使用_RequiresNew方法会直接新建一个事务
不使用_RequiresNew会判断堆栈中是否已有事务，有就直接使用栈顶事务，没有就新建事务
之后封装成context，压栈

   public void begin(int transType) throws NotSupportedException, SystemException {
     switch (transType) {
     case 1: 
       if (this.tranStack.isEmpty()) {
         createTransaction(TransactionContextType.SOURCE);
       } else {
         createTransaction(TransactionContextType.JOINED);
       }
       break;
     case 3: 
       createTransaction(TransactionContextType.SOURCE);
       break;
     case 4: 
       if (this.tranStack.isEmpty()) {
         throw new SystemException();
       }
       createTransaction(TransactionContextType.JOINED);
       
       break;
     case 5: 
       if (!this.tranStack.isEmpty()) {
         throw new SystemException();
       }
       createTransaction(TransactionContextType.NULL);
       break;
     case 2: 
       if (!this.tranStack.isEmpty()) {
         createTransaction(TransactionContextType.NULL);
       } else {
         createTransaction(TransactionContextType.JOINED);
       }
       break;
     case 0: 
       createTransaction(TransactionContextType.NULL);
       break;
     case 11: 
       createTransaction(TransactionContextType.JOINED);
       try {
         setCurInvokeSavePoint();
       } catch (SQLException e) {
         throw new NotSupportedException("savePoint error!");
       }
     case 6: case 7: case 8: 
     case 9: case 10: default: 
       throw new NotSupportedException("trans type error!");
     }
     
   }

 private UAPTransactionContext createTransaction(TransactionContextType transType) throws 	SystemException
   {
     UAPTransaction uapTran = null;
     if (transType == TransactionContextType.SOURCE) {
       uapTran = new UAPTransaction();
     }
     if (transType == TransactionContextType.JOINED) {
       if (this.tranStack.isEmpty()) {
         throw new SystemException("no source Transaction,can not join ");
       }
       uapTran = (UAPTransaction)getTranContext().getTransaction();
     } else {
       uapTran = new UAPTransaction();
     }
     
     UAPTransactionContext tranText = new UAPTransactionContext(uapTran);
     tranText.setTransType(transType);
     this.tranStack.push(tranText);
     return tranText;
   }

　　afterCallMethod同理

   protected void afterCallMethod(int methodId, Exception exception)
     throws java.rmi.RemoteException
   {
......
     boolean isCmt = ((HomeBase)getEJBLocalHome()).getEJBBeanDescriptor().isCmt();
     
     if (isCmt) {
       getIerpTransactionManagerProxy().end(exception);
       setIerpTransactionManagerProxy(null);
     }
     else
     {
       getIerpUserTransaction().unbindCurrentThread();
     }
......
   }

UAPTransactionManager中的end方法，其中会判断目标方法是否抛出异常

   public void end(Exception ex)
   {
     IUAPTransactionManager m_tranManager = (IUAPTransactionManager)tm_local.get();
     try {
       if (ex != null) {
         if (m_tranManager.getTranContext().needRBPoint()) {
           if (!((UAPTransaction)m_tranManager.getTranContext().getTransaction()).getRollbackOnly())
           {
             m_tranManager.rollBackToCurInvokePoint();
           }
         }
         else {
           m_tranManager.setCurTransRollBack();
         }
       }
       m_tranManager.commit();
     } catch (Exception e) {
       log.error("", e);
     }
   }

假如抛出异常，最终会调用UAPTransaction的setRollbackOnly方法，值得注意的是这里的rollback仅仅是设置了一个回滚标志，没有真正回滚，之后会说这样会导致什么问题。

最终会调用commit方法，这里的commit也不是单纯的提交，他会判断之前是否有设置回滚标志来进行统一回滚，整个事务调用到此完成。

知道了以上事务的原理后，假如我们代码里面有这样一种场景，即便调用方法B的时候捕捉异常且不向外抛出，之后的数据库操作也会回滚。其中是因为调用方法B之后代理会将当前的事务设置一个回滚标志，当完成方法A之后，整个事务会根据回滚标志统一回滚。

methodA__RequiresNew{
ClassB cb = NCLocate.lookup(ClassB.class);
try{
cb.methodB();
}catch(e){

}
//insert to db
insertsomething();
}

同大多数框架一样，NC实现了JTA规范，拓展：

https://www.jianshu.com/p/3938e7172443

https://blog.csdn.net/u014235678/article/details/103898538

3.checkpoint
4.Synchronization

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