spring 面试题

1.事务何时回滚

默认spring事务只在发生未被捕获的 runtimeexcetpion时才回滚。  
   spring aop  异常捕获原理：被拦截的方法需显式抛出异常，并不能经任何处理，这样aop代理才能捕获到方法的异常，才能进行回滚，默认状况下aop只捕获runtimeexception的异常，但能够经过  
    
配置来捕获特定的异常并回滚  
  换句话说在service的方法中不使用try catch 或者在catch中最后加上throw new runtimeexcetpion（），这样程序异常时才能被aop捕获进而回滚
  解决方案： 
  方案1.

    例如service层处理事务，那么service中的方法中不作异常捕获，或者在catch语句中最后增长throw new RuntimeException()语句，以便让aop捕获异常再去回滚，而且在service上层（webservice客户端，view层action）要继续捕获这个异常并处理
  方案2.

    在service层方法的catch语句中增长：

    TransactionAspectSupport.currentTransactionStatus().setRollbackOnly();语句，手动回滚，这样上层就无需去处理异常（如今项目的作法）

RuleBasedTransactionAttribute
/**
	 * Winning rule is the shallowest rule (that is, the closest in the
	 * inheritance hierarchy to the exception). If no rule applies (-1),
	 * return false.
	 * @see TransactionAttribute#rollbackOn(java.lang.Throwable)
	 */
	@Override
	public boolean rollbackOn(Throwable ex) {
		if (logger.isTraceEnabled()) {
			logger.trace("Applying rules to determine whether transaction should rollback on " + ex);
		}

		RollbackRuleAttribute winner = null;
		int deepest = Integer.MAX_VALUE;

		if (this.rollbackRules != null) {
			for (RollbackRuleAttribute rule : this.rollbackRules) {
				int depth = rule.getDepth(ex);
				if (depth >= 0 && depth < deepest) {
					deepest = depth;
					winner = rule;
				}
			}
		}

		if (logger.isTraceEnabled()) {
			logger.trace("Winning rollback rule is: " + winner);
		}

		// User superclass behavior (rollback on unchecked) if no rule matches.
		if (winner == null) {
			logger.trace("No relevant rollback rule found: applying default rules");
			return super.rollbackOn(ex);
		}

		return !(winner instanceof NoRollbackRuleAttribute);
	}

//经过源码能够看出，spring默认只对，RuntimeException和Error作处理了
DefaultTransactionAttribute
@Override
public boolean rollbackOn(Throwable ex) {
		return (ex instanceof RuntimeException || ex instanceof Error);
}