java - Spring事务配置在service层，传播规则为required，方法中究竟应该是调用service还是多个dao比较好？

Question

Spring中事务配置如下：

<tx:advice id="txAdvice" transaction-manager="transactionManager">
    <tx:attributes>
        <tx:method name="delete*" propagation="REQUIRED" read-only="false" 
                   rollback-for="java.lang.Exception"/>
        <tx:method name="insert*" propagation="REQUIRED" read-only="false" 
                   rollback-for="Exception" />
        <tx:method name="update*" propagation="REQUIRED" read-only="false" 
                   rollback-for="java.lang.Exception" />
        <tx:method name="save*" propagation="REQUIRED" read-only="false" 
                   rollback-for="Exception" />
        <tx:method name="*" propagation="REQUIRED" read-only="true"/>
    <:attributes>
<:advice>

现在ServiceA中有一个方法methodA，那么在ServiceA中应该注入ServiceB，ServiceC呢，还是DaoB,DaoC,然后在methodA中去保存B，C，保证B,C同时保存成功，或同时失败!

---

答：

既可以单独注入service，也可以单独注入dao，关键是，spring容器的事务管理默认只截获未检查异常RuntimeException。上边配置的rollback-for="java.lang.Exception"其实不用配置。配置如下

<tx:advice id="txAdvice" transaction-manager="transactionManager">
    <tx:attributes>
        <tx:method name="delete*" propagation="REQUIRED" read-only="false"  />
        <tx:method name="insert*" propagation="REQUIRED" read-only="false"   />
        <tx:method name="update*" propagation="REQUIRED" read-only="false"   />
        <tx:method name="save*" propagation="REQUIRED" read-only="false"  />
        <tx:method name="*" propagation="REQUIRED" read-only="true"/>
    <:attributes>
<:advice>

解决方案是：

• 如果代码中使用了try...catch...捕获了检查型异常，意味着程序员自己必须要解决异常，必须知道如何解决异常。通常的做法是：将检查型的异常在catch块中重新抛出为Runtime Exception，这样Spring容器就会截获该异常，进行事务回滚处理 。如下

try {
   .....
}catch( CheckedException e ) {
    logger.error(e);
    throw new RuntimeException(e);
}

注意，不使用try...catch...，而在方法签名后向外抛出检查型异常的行为不可取，事务也不会回滚。

• 如果代码中没有使用try抛出了未检查异常，则Spring容器会自动截获异常，进行事务回滚处理。

Answer 1

If you want to know more about Spring transaction mechanism, you can read these articles of mine:

1. Detailed explanation of Spring Transaction - Transaction Isolation

2. Detailed explanation of Spring Transaction - Transaction Propagation mode

3. Detailed explanation of Spring Transaction - Manual rollback of transactions

4. Detailed explanation of Spring Transaction - transaction rollback mechanism when exceptions occur

Answer 2

In fact, this kind of thing is done according to needs, and transactions will be automatically merged. However, as a design consideration, try to call dao so that different services can be uncoupled.

Answer 3

Generally, it is more complicated for us in Service的方法上会进行事务的定义，特别是如果有控制传播行为的场景，那放入dao就和放入service不同了。因为dao肯定都是在一个大事务下了，service.