Intercepting method with Spring AOP using only annotations

Question

In my Spring context file I have something like this:

<bean id="userCheck" class="a.b.c.UserExistsCheck"/>
<aop:config>
      <aop:aspect ref="userCheck">
         <aop:pointcut id="checkUser"
                expression="execution(* a.b.c.d.*.*(..)) &amp;&amp; args(a.b.c.d.RequestObject)"/>
         <aop:around pointcut-ref="checkUser" method="checkUser"/>
      </aop:aspect>
</aop:config>    

a.b.c.UserExistsCheck looks like this:

@Aspect
public class UserExistsCheck {

@Autowired
private UserInformation userInformation;

public Object checkUser(ProceedingJoinPoint pjp) throws Throwable {
    int userId = ... //get it from the RequestObject passed as a parameter
    if (userExists(userId)) {
        return pjp.proceed();
    } else {
        return new ResponseObject("Invalid user);
    }
}

And the class that is being intercepted with this stuff looks like this:

public class Klazz {
    public ResponseObject doSomething(RequestObject request) {...}
}

This works. UserExistCheck is executed as desired before the call is passed to Klazz. The problem is that this is the only way I got it working. To get this working by using annotations instead of the context file seems to be just too much for my small brain. So... how exactly should I annotate the methods in UserExistsCheck and Klazz? And do I still need something else too? Another class? Still something in the context file?

Answer 1

Have you enabled annotation-based AOP? The documentation says you have to add

<aop:aspectj-autoproxy/>

to your spring configuration. Then you need to add an annotation in front of your checkUser method. It looks like you want @Around advice, as described here.

@Aspect
public class UserExistsCheck {

  @Around("execution(* a.b.c.d.*.*(..)) && args(a.b.c.d.RequestObject)")
  public Object checkUser(ProceedingJoinPoint pjp) throws Throwable {

Answer 2

From the example code you've provided, it appears that you're trying to create advice for a class that doesn't implement any interfaces. As described in the Proxying Mechanisms section of the Spring docs, if you're going to do this, you'll need to enable CGLIB:

<aop:aspectj-autoproxy proxy-target-class="true" />

I've personally found this to be a bit more finicky than the documentation indicates it should be, and though it does work if all of the stars are aligned just right, it's often easier--and preferable from a design standpoint--to declare your AOP advice on an interface, as follows. (Note that you'll need to obtain your instance of KlazzImpl from your BeanFactory/ApplicationContext.)

public class Klazz {
  ResponseObject doSomething(RequestObject request);
}

public class KlazzImpl implements Klazz {
  public ResponseObject doSomething(RequestObject request) {...}
}

Additionally, your use of the args expression is a little bit off. See the following:

@Aspect
public class UserExistsCheck {
  @Autowired
  private UserInformation userInformation;

  @Around("execution(* a.b.c.d.*.*(..)) && args(reqObj)")
  public Object checkUser(ProceedingJoinPoint pjp, a.b.c.d.RequestObject reqObj) throws Throwable {
      // ...
  }
}

These changes should do the job.