/*** @author 王政* @date 2006-11-24* @note 转载自http://www.iteye.com/topic/35907?page=1*/ ********TransactionDefinition 接口定义*******************/*** Support a current transaction, create a new one if none exists.* Analogous to EJB transaction attribute of the same name.*

This is typically the default setting of a transaction definition.*/int PROPAGATION_REQUIRED = 0;/*** Support a current transaction, execute non-transactionally if none exists.* Analogous to EJB transaction attribute of the same name.*

Note: For transaction managers with transaction synchronization,* PROPAGATION_SUPPORTS is slightly different from no transaction at all,* as it defines a transaction scopp that synchronization will apply for.* As a consequence, the same resources (JDBC Connection, Hibernate Session, etc)* will be shared for the entire specified scope. Note that this depends on* the actual synchronization configuration of the transaction manager.* @see org.springframework.transaction.support.AbstractPlatformTransactionManager#setTransactionSynchronization*/int PROPAGATION_SUPPORTS = 1;/*** Support a current transaction, throw an exception if none exists.* Analogous to EJB transaction attribute of the same name.*/int PROPAGATION_MANDATORY = 2;/*** Create a new transaction, suspend the current transaction if one exists.* Analogous to EJB transaction attribute of the same name.*

Note: Actual transaction suspension will not work on out-of-the-box* on all transaction managers. This in particular applies to JtaTransactionManager,* which requires the javax.transaction.TransactionManager to be* made available it to it (which is server-specific in standard J2EE).* @see org.springframework.transaction.jta.JtaTransactionManager#setTransactionManager*/int PROPAGATION_REQUIRES_NEW = 3;/*** Execute non-transactionally, suspend the current transaction if one exists.* Analogous to EJB transaction attribute of the same name.*

Note: Actual transaction suspension will not work on out-of-the-box* on all transaction managers. This in particular applies to JtaTransactionManager,* which requires the javax.transaction.TransactionManager to be* made available it to it (which is server-specific in standard J2EE).* @see org.springframework.transaction.jta.JtaTransactionManager#setTransactionManager*/int PROPAGATION_NOT_SUPPORTED = 4;/*** Execute non-transactionally, throw an exception if a transaction exists.* Analogous to EJB transaction attribute of the same name.*/int PROPAGATION_NEVER = 5;/*** Execute within a nested transaction if a current transaction exists,* behave like PROPAGATION_REQUIRED else. There is no analogous feature in EJB.*

Note: Actual creation of a nested transaction will only work on specific* transaction managers. Out of the box, this only applies to the JDBC* DataSourceTransactionManager when working on a JDBC 3.0 driver.* Some JTA providers might support nested transactions as well.* @see org.springframework.jdbc.datasource.DataSourceTransactionManager*/int PROPAGATION_NESTED = 6;*************************************************************************在这篇文章里，他用两个嵌套的例子辅助分析，我这里直接引用了。********************sample***********************ServiceA {/*** 事务属性配置为 PROPAGATION_REQUIRED*/void methodA() {ServiceB.methodB();}}ServiceB {/*** 事务属性配置为 PROPAGATION_REQUIRED*/void methodB() {}}      *************************************************我们这里一个个分析吧1： PROPAGATION_REQUIRED加入当前正要执行的事务不在另外一个事务里，那么就起一个新的事务比如说，ServiceB.methodB的事务级别定义为PROPAGATION_REQUIRED, 那么由于执行ServiceA.methodA的时候，ServiceA.methodA已经起了事务，这时调用ServiceB.methodB，ServiceB.methodB看到自己已经运行在ServiceA.methodA的事务内部，就不再起新的事务。而假如ServiceA.methodA运行的时候发现自己没有在事务中，他就会为自己分配一个事务。这样，在ServiceA.methodA或者在ServiceB.methodB内的任何地方出现异常，事务都会被回滚。即使ServiceB.methodB的事务已经被提交，但是ServiceA.methodA在接下来fail要回滚，ServiceB.methodB也要回滚2：   PROPAGATION_SUPPORTS如果当前在事务中，即以事务的形式运行，如果当前不再一个事务中，那么就以非事务的形式运行这就跟平常用的普通非事务的代码只有一点点区别了。不理这个，因为我也没有觉得有什么区别3：   PROPAGATION_MANDATORY必须在一个事务中运行。也就是说，他只能被一个父事务调用。否则，他就要抛出异常。4：   PROPAGATION_REQUIRES_NEW这个就比较绕口了。 比如我们设计ServiceA.methodA的事务级别为PROPAGATION_REQUIRED，ServiceB.methodB的事务级别为PROPAGATION_REQUIRES_NEW，那么当执行到ServiceB.methodB的时候，ServiceA.methodA所在的事务就会挂起，ServiceB.methodB会起一个新的事务，等待ServiceB.methodB的事务完成以后，他才继续执行。他与PROPAGATION_REQUIRED 的事务区别在于事务的回滚程度了。因为ServiceB.methodB是新起一个事务，那么就是存在两个不同的事务。如果ServiceB.methodB已经提交，那么ServiceA.methodA失败回滚，ServiceB.methodB是不会回滚的。如果ServiceB.methodB失败回滚，如果他抛出的异常被ServiceA.methodA捕获，ServiceA.methodA事务仍然可能提交。5：   PROPAGATION_NOT_SUPPORTED当前不支持事务。比如ServiceA.methodA的事务级别是PROPAGATION_REQUIRED ，而ServiceB.methodB的事务级别是PROPAGATION_NOT_SUPPORTED ，那么当执行到ServiceB.methodB时，ServiceA.methodA的事务挂起，而他以非事务的状态运行完，再继续ServiceA.methodA的事务。6：   PROPAGATION_NEVER不能在事务中运行。假设ServiceA.methodA的事务级别是PROPAGATION_REQUIRED， 而ServiceB.methodB的事务级别是PROPAGATION_NEVER ，那么ServiceB.methodB就要抛出异常了。7：   PROPAGATION_NESTED理解Nested的关键是savepoint。他与PROPAGATION_REQUIRES_NEW的区别是，PROPAGATION_REQUIRES_NEW另起一个事务，将会与他的父事务相互独立，而Nested的事务和他的父事务是相依的，他的提交是要等和他的父事务一块提交的。也就是说，如果父事务最后回滚，他也要回滚的。而Nested事务的好处是他有一个savepoint。*****************************************ServiceA {/*** 事务属性配置为 PROPAGATION_REQUIRED*/void methodA() {try {//savepointServiceB.methodB();    //PROPAGATION_NESTED 级别} catch (SomeException) {// 执行其他业务, 如 ServiceC.methodC();}}}********************************************也就是说ServiceB.methodB失败回滚，那么ServiceA.methodA也会回滚到savepoint点上，ServiceA.methodA可以选择另外一个分支，比如ServiceC.methodC，继续执行，来尝试完成自己的事务。但是这个事务并没有在EJB标准中定义。二、Isolation Level(事务隔离等级):