why is this Spring AOP pointcut not triggered?

Question

I'm writing very basic schema-based Spring AOP, here's the .xml

<bean id="aoplistener" class="tao.zhang.Listener"/> <aop:config> <aop:aspect ref="aoplistener"> <aop:pointcut id="whenCalled" expression="execution(* callme(..))" /> <aop:after method="scream" pointcut-ref="whenCalled" /> </aop:aspect> </aop:config>

The method scream() in tao.zhang.Listener just prints out some text, and is supposed to be executed whenever a method callme() is called.

I have a bean called logger which has the methods log() and callme()

public void log(){ callme(); System.out.println("Hello from logger ~~~~~~~~~~~~~~~~~~~"); } public void callme(){ System.out.println("I'm called"); }

Note that callme() is called by log()

Now I have a scheduler which calls log() every 5 seconds:

<task:scheduler id="myScheduler" pool-size="10"/> <task:scheduled-tasks scheduler="myScheduler"> <task:scheduled ref="logger" method="log" fixed-rate="5000"/> </task:scheduled-tasks>

Strangely, scream() is not invoked, but if callme() is called directly:

<task:scheduler id="myScheduler" pool-size="10"/> <task:scheduled-tasks scheduler="myScheduler"> <task:scheduled ref="logger" method="callme" fixed-rate="5000"/> </task:scheduled-tasks>

scream() is invoked!

Any suggestions? It seems to me that this pointcut doesn't match methods called inside another method ...

Donal Fellows · Accepted Answer · 2012-02-10 06:36:05Z

11

Spring AOP only traps a method call when the call is done through a bean handle (because the interceptor is applied through the use of a proxy object) and not when the method is called directly.

To make your code work, you need to either switch to using AspectJ (which works by rewriting the class's bytecode, which allows it to intercept far more things and to do so more transparently) or to change how you call callme() so that it is via a bean handle:

SomeClass selfRef; public void log(){ selfRef.callme(); System.out.println("Hello from logger ~~~~~~~~~~~~~~~~~~~"); } public void callme(){ System.out.println("I'm called"); }

You need to configure the selfRef field explicitly; it won't be autowired.

answered Feb 10, 2012 at 6:36

Donal Fellows

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4 Comments

Tao Over a year ago

Yeah, Thanks a lot! I was just chewing this sentence from the spring manual book : Spring AOP only supports method execution join points for Spring beans

Donal Fellows Over a year ago

I found that it helped me a lot to know how Spring worked. If it does anything fancy (including AOP) it gives you a proxy object that contains the interception points it requires. That proxy object — the bean handle, if you will — is how you are supposed to do all calls on the bean, and you shouldn't go behind Spring's back by calling via this (which is what a raw callme() does; the this. is implicit).

Tao Over a year ago

I now feel that Spring AOP is hardly useful in many cases. In my current project, I want to take some log whenever callme() is called, and callme() is used by various methods in this class as a sub-routine, which is a very common situation.

Donal Fellows Over a year ago

@Tao: Well, your choices are to refactor into two (or more) beans, call by the self-handle trick, or to use AspectJ to do the interception (as that can do what you want). In my code, I mostly dealt with things by refactoring and I also had some use of the self-trick, but I avoided AspectJ as I already had other bytecode rewriting systems in place and didn't want to try to get the whole system to play nicely. (It was complex enough already!)

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