java - Spring AOP - Invoking advice from catch block

Question

Purpose: Send an email to admin every time an exception occurs while executing business logic.

Till now I have come across "throwing advice" which is fine and gets executed when an exception is raised from the target method.

This could have worked well for me but I have to do some additional processing in terms of setting request attribute and next page. I don't think it would be a good idea to share the objects from target class with advice by making those objects static. The code scenario is shown below:

try{
   //normal processing
} catch (AuthenticationException ae) {
   ae.printStackTrace();
   req.setAttribute("msg", ae.getMessage());

   //execute advice at this point

   return loginPage;
}

Pls. see the point where I want to execute the advice and suggest solution accordingly.

Best Regards

Answer 1

I know you want to avoid full AspectJ as opposed to Spring AOP. (BTW, I wonder why many people are so afraid of it.) Anyway, in AspectJ is is really easy to intercept exception handler execution (=catch blocks) by means of the handler() pointcut. There is one limitation though: It only works with before() advice, not after() or around(). This is due to compiler limitations. Look at JVM byte code of exception handlers and you will see that there is no way to detect the end of a handler block. Anyway, because the concept is related to the original question, I want to show here how it is done. I have created a little driver application and a very simple aspect:

import java.util.Random;
import javax.naming.AuthenticationException;

public class Application {
    public static void main(String[] args) {
        Application app = new Application();
        System.out.println(app.foo(1, "two", 3d));
        System.out.println(app.bar("one", 2d, 3));
        System.out.println(app.zot(1d, 2, "three"));
    }

    public String foo(int i, String string, double d) {
        try {
            if (new Random().nextBoolean())
                throw new AuthenticationException("wrong password");
        }
        catch (AuthenticationException e) {
            return "return value from catch block";
        }
        return "normal return value";
    }

    public String bar(String string, double d, int i) {
        try {
            if (new Random().nextBoolean())
                throw new IllegalArgumentException("I don't like your arguments");
        }
        catch (IllegalArgumentException e) {
            return "return value from catch block";
        }
        return "normal return value";
    }

    public String zot(double d, int i, String string) {
        try {
            int n = 2/0;
        }
        catch (Throwable t) {
            return "return value from catch block";
        }
        return "normal return value";
    }
}

As you can see, methods foo and bar throw exceptions based on random values in ca. 50% of all cases, whereas zot always throws a division by zero exception. So the output will differ from run to run.

So how do we find out what is going on if all exceptions are silently swallowed and not logged? Like so:

import java.util.logging.Logger;

public aspect ExceptionLoggingAspect {
    final Logger log = Logger.getLogger(ExceptionLoggingAspect.class.getName());

    before(Throwable t) : handler(Throwable+) && args(t) {
        log.warning(thisJoinPointStaticPart + "  ->  " + t);
    }
}

This is really simple and elegant and works throughout your application. Here is some test output:

Apr 6, 2013 12:15:43 PM ExceptionLoggingAspect ajc$before$ExceptionLoggingAspect$1$3d90b181
WARNING: handler(catch(AuthenticationException))  ->  javax.naming.AuthenticationException: wrong password
return value from catch block
Apr 6, 2013 12:15:43 PM ExceptionLoggingAspect ajc$before$ExceptionLoggingAspect$1$3d90b181
WARNING: handler(catch(IllegalArgumentException))  ->  java.lang.IllegalArgumentException: I don't like your arguments
return value from catch block
Apr 6, 2013 12:15:43 PM ExceptionLoggingAspect ajc$before$ExceptionLoggingAspect$1$3d90b181
WARNING: handler(catch(Throwable))  ->  java.lang.ArithmeticException: / by zero
return value from catch block

In the advice you can do more, e.g. access this and read/update some properties and so fort.