JTA事务总结（二）
自：http://blog.sina.com.cn/s/blog_661a3fce0100msjb.html
记得EJB的部署文件的事务属性<trans-attribute>RequiresNew</trans-attribute>的情况，在调用该EJB函数时如果已经存在一个事务进行中，那么要求容器挂起该事务，启动新的事务进行函数调用，直到函数结束后，再恢复原来的事务继续进行。
也许你会想到用以下的方式进行:
UserTransaction tx = (UserTransaction)ctx.lookup("javax.transaction.UserTransaction");
UserTransaction tx2 = (UserTransaction)ctx.lookup("javax.transaction.UserTransaction");
tx.begin();
tx2.begin();
tx2.commit();
tx.commit();
以上代码会抛出如下异常：
javax.transaction.NotSupportedException: Another transaction is associated with this thread.
查找了sun的 JTA specification 说明如下：
The UserTransaction.begin method starts a global transaction and associates the transaction with the calling thread. The transaction-to-thread association is managed transparently by the Transaction Manager. Support for nested tranactions is not required. The UserTransaction.begin method throws the NotSupportedException when the calling thread is already associated with a transaction and the transaction manager implementation does not support nested transactions.
看来weblogic的Transaction没有实现嵌套功能，那么容器如何RequiresNew的ejb事务情况呢，就得借助于TransactionManager类了
tm = (TransactionManager)ctx.lookup("javax.transaction.TransactionManager");
tx = (UserTransaction)ctx.lookup("javax.transaction.UserTransaction");
tx.begin();
...
transaction = tm.suspend();
doNestedTransaction();
tm.resume(transaction);
...
tx.commit();
其实以上问题的顺利解决都归功于sun完整的官方资料，想想从事Java快两年了我的大部分知识都是来源于“东拼西凑”：书籍、论坛、项目...看来是该花点时间好好读读sun网站的各种specification了。
http://java.sun.com/products/jta/index.html
