spring事务的传播属性--@Transaction的Propagation属性

public enum Propagation {

	//默认值
	//当前有事务，就加入这个事务，没有事务，就新建一个事务
	REQUIRED(TransactionDefinition.PROPAGATION_REQUIRED),
	
  	//当前有事务，就加入这个事务，没有事务，就以非事务的方式执行
	SUPPORTS(TransactionDefinition.PROPAGATION_SUPPORTS),

	//当前有事务，就加入这个事务，没有事务，就抛出异常
	MANDATORY(TransactionDefinition.PROPAGATION_MANDATORY),

	//新建一个事务执行，如果当前有事务，就把当前的事务挂起
	REQUIRES_NEW(TransactionDefinition.PROPAGATION_REQUIRES_NEW),

	//在无事务状态下执行，如果当前有事务，就把当前的事务挂起
	NOT_SUPPORTED(TransactionDefinition.PROPAGATION_NOT_SUPPORTED),

	//在无事务状态下执行，如果当前有事务，会抛出异常
	NEVER(TransactionDefinition.PROPAGATION_NEVER),

	/**
	 * Execute within a nested transaction if a current transaction exists,
	 * behave like PROPAGATION_REQUIRED else. There is no analogous feature in EJB.
	 * <p>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
	 */
	 //当前有事务，就新建一个事务，嵌套执行，当前无事务，就新建一个事务执行
	 //这个看了不同的文章，说法不一致，建议看下源码注释。
	NESTED(TransactionDefinition.PROPAGATION_NESTED);
	
	private final int value;

	Propagation(int value) { this.value = value; }

	public int value() { return this.value; }

}