spring源码自定义异常分析

查了好久，才找到spring事务对自定义异常的分析和应用，看类RuleBasedTransactionAttribute，该类的简介如下：

TransactionAttribute implementation that works out whether a given exception should cause transaction rollback by applying a number of rollback rules, both positive and negative. If no rules are relevant to the exception, it behaves like DefaultTransactionAttribute (rolling back on runtime exceptions).

spring对指定异常的回滚在于 rollbackOn 方法，该类默认的实现是在DefaultTransactionAttribute类中，而RuleBasedTransactionAttribute重写了该方法，简化后代码如下：

/**
* 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) {
RollbackRuleAttribute winner = null;
int deepest = Integer.MAX_VALUE;

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

// 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);
}

另外，如果我们需要在事务控制的service层类中使用try catch 去捕获异常后，会使事务回滚机制失效，因为该类的异常并没有抛出，即不触发事务管理机制。怎样才能既用try catch去捕获异常，又让出现异常后spring回滚呢？代码解决如下：

//假设这是一个service类的片段
try{
//出现异常
} catch (Exception e) {
e.printStackTrace();
//设置手动回滚(重点！！！！！！)
TransactionAspectSupport.currentTransactionStatus().setRollbackOnly();
}
//此时return语句能够执行
return  xxx;