spring事务传播级别（枚举项意义）

spring事务的传播级别不知道可就尴尬了

（Propagation，一个枚举类）

1.REQUIRED(TransactionDefinition.PROPAGATION_REQUIRED)，默认级别，

Support a current transaction, create a new one if none exists. 支持当前事务，不存在就创建新的

2.SUPPORTS(TransactionDefinition.PROPAGATION_SUPPORTS),

Support a current transaction, execute non-transactionally if none exists.支持当前事务，不存在就以非事务方式运行

3.MANDATORY(TransactionDefinition.PROPAGATION_MANDATORY),

upport a current transaction, throw an exception if none exists.支持当前事务，没有就抛出异常

4.REQUIRES_NEW(TransactionDefinition.PROPAGATION_REQUIRES_NEW),

Create a new transaction, and suspend the current transaction if one exists.创建新的事务，当前事务存在则挂起

5.NOT_SUPPORTED(TransactionDefinition.PROPAGATION_NOT_SUPPORTED),

Execute non-transactionally, suspend the current transaction if one exists.以非事务方式运行，当前事务存在则挂起

6.NEVER(TransactionDefinition.PROPAGATION_NEVER),

Execute non-transactionally, throw an exception if a transaction exists。非事务方式运行，有事务抛异常

7.NESTED(TransactionDefinition.PROPAGATION_NESTED);

Execute within a nested transaction if a current transaction exists, behave like PROPAGATION_REQUIRED else.

在嵌套事务内运行，很像PROPAGATION_REQUIRED