java - 间接 Hibernate/JPA 方法调用丢失事务

Question

我在这段代码中使用 Spring/JPA2/hibernate:

class A {
  @Autowired
  B b;

  @RequestMapping("/test")
  public void test(final HttpServletRequest r1, HttpServletResponse r2) throws ... {

    b.inner();   // Works

    b.outer();   // javax.persistence.TransactionRequiredException: 
                 // no transaction is in progress ... :|
}

@Component
class B {
   @PersistenceContext
   EntityManager em;

   public void outer() { inner(); }

   @Transactional
   public void inner() { em.flush(); }
}

为什么 inner() 只有在间接调用时才会松动事务？

Answer 1

http://static.springsource.org/spring/docs/current/reference/transaction.html#transaction-declarative-annotations

In proxy mode (which is the default), only external method calls coming in through the proxy are intercepted. This means that self-invocation, in effect, a method within the target object calling another method of the target object, will not lead to an actual transaction at runtime even if the invoked method is marked with @Transactional.

Consider the use of AspectJ mode (see mode attribute in table below) if you expect self-invocations to be wrapped with transactions as well. In this case, there will not be a proxy in the first place; instead, the target class will be weaved (that is, its byte code will be modified) in order to turn @Transactional into runtime behavior on any kind of method.

@Autowired 引用 B b(在类 A 内)，用 Spring AOP 事务感知代理包装。

当 b.inner() 被调用时，您是在事务感知实例上调用它，它被标记为 @Transactional。因此启动了 Spring 管理的事务。

当 b.outer() 被调用时，它也是在事务感知实例上，但它不是 @Transactional。因此，Spring 管理的事务未启动。

一旦您进入 outer() 的调用，对 inner() 的调用不会通过事务感知代理，它被直接调用。它与 this.inner() 相同。由于您是直接调用它，而不是通过代理调用它，因此它不具有 Spring 事务感知语义。

由于尚未启动任何事务，这将导致 TransactionRequiredException。

可能的解决方案包括使方法 outer() @Transactional。

   @Transactional
   public void outer() { inner(); }

或者使整个类成为@Transactional。

@Transactional   
@Component
class B {
   @PersistenceContext
   EntityManager em;