Java annotation for wrapping a method

annotations, java, methods

Solution

To do this, you would need some AOP framework that would use a proxy around your method. This proxy would catch the exception and execute the finally block. Quite frankly, if you don't use a framework supporting AOP already, I'm not sure I would use one just to save these few lines od code.

You could use the following pattern to do this in a more elegant way, though:

public void doSomething() {
    logAndCleanup(new Callable<Void>() {
        public Void call() throws Exception {
            implementationOfDoSomething();
            return null;
        }
    });
}

private void logAndCleanup(Callable<Void> callable) {
    try {
        callable.call();
    } 
    catch (Exception e) {
        MyEnv.getLogger().log(e);
    } 
    finally {
        genericCleanUpMethod();
    }
}

I just used `Callable<Void>` as an interface, but you could define your own `Command` interface:

public interface Command {
    public void execute() throws Exception;
}

and thus avoid the need to use a generic `Callable<Void>` and return null from the Callable.

EDIT: in case you want to return something from your methods, then make the `logAndCleanup()` method generic. Here's a complete example:

public class ExceptionHandling {
    public String doSomething(final boolean throwException) {
        return logAndCleanup(new Callable<String>() {
            public String call() throws Exception {
                if (throwException) {
                    throw new Exception("you asked for it");
                }
                return "hello";
            }
        });
    }

    public Integer doSomethingElse() {
        return logAndCleanup(new Callable<Integer>() {
            public Integer call() throws Exception {
                return 42;
            }
        });
    }

    private <T> T logAndCleanup(Callable<T> callable) {
        try {
            return callable.call();
        }
        catch (Exception e) {
            System.out.println("An exception has been thrown: " + e);
            throw new RuntimeException(e); // or return null, or whatever you want
        }
        finally {
            System.out.println("doing some cleanup...");
        }
    }

    public static void main(String[] args) {
        ExceptionHandling eh = new ExceptionHandling();

        System.out.println(eh.doSomething(false));
        System.out.println(eh.doSomethingElse());
        System.out.println(eh.doSomething(true));
    }
}

EDIT : And with Java 8, the wrapped code can be a bit prettier :

public String doSomething(final boolean throwException) {
    return logAndCleanup(() -> {                
        if (throwException) {
            throw new Exception("you asked for it");
        }
        return "hello";                
    });
}

Problem

I have a lot of boilerplate code that basically follows this pattern: ``` function doSomething() { try { [implementation] [implementation] [implementation] [implementation] } catch (Exception e) { MyEnv.getLogger().log(e); } finally { genericCleanUpMethod(); } } ``` I'd love to create my own annotation to clean my code up a bit: ``` @TryCatchWithLoggingAndCleanUp function doSomething() { [implementation] [implementation] [implementation] [implementation] } ``` The method signatures vary wildly (depending on the actual implementation of the method), but the boilerplate try/catch/finally part is always the same. The annotation I have in mind would automatically wrap the contents of the annotated method with the whole `try...catch...finally` hoopla. I've searched high and low for a straightforward way to do this, but have found nothing. I don't know, maybe I just can't see the woods for all the annotated trees. Any pointers on how I might implement such an annotation would be greatly appreciated.

Original source

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