spring事务锁
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事务的传播行为和隔离级别[transaction behavior and isolated level]
Spring中事务的定义：
一、Propagation ：
key属性确定代理应该给哪个方法增加事务行为。这样的属性最重要的部份是传播行为。有以下选项可供使用：
PROPAGA TION_REQUIRED--支持当前事务，如果当前没有事务，就新建一个事务。这是最常见的选择。
PROPAGA TION_SUPPORTS--支持当前事务，如果当前没有事务，就以非事务方式执行。PROPAGA TION_MANDA TORY--支持当前事务，如果当前没有事务，就抛出异常。PROPAGA TION_REQUIRES_NEW--新建事务，如果当前存在事务，把当前事务挂起。PROPAGA TION_NOT_SUPPORTED--以非事务方式执行操作，如果当前存在事务，就把当前事务挂起。
PROPAGA TION_NEVER--以非事务方式执行，如果当前存在事务，则抛出异常。
很多人看到事务的传播行为属性都不甚了解，我昨晚看了j2ee without ejb的时候，看到这里也不了解，甚至重新翻起数据库系统的教材书，但是也没有找到对这个的分析。今天搜索，找到一篇极好的分析文章，虽然这篇文章是重点分析PROPAGA TION_REQUIRED 和PROPAGA TION_REQUIRED_NESTED的
解惑spring 嵌套事务
/**
* @author 王政
* @date 2006-11-24
* @note 转载自/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.AbstractPlatformT ransactionManager#setT ransa ctionSynchronization
*/
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 JtaT ransactionManager,
* which requires the javax.transaction.T ransactionManager to be
* made available it to it (which is server-specific in standard J2EE).
* @see org.springframework.transaction.jta.JtaT ransactionManager#setT ransactionManager */
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 JtaT ransactionManager, * which requires the javax.transaction.T ransactionManager to be
* made available it to it (which is server-specific in standard J2EE).
* @see org.springframework.transaction.jta.JtaT ransactionManager#setT ransactionManager */
int PROPAGATION_NOT_SUPPORTED = 4;