Question

I need to create a proxy for a class. I do not have access to the concrete subject but only to the subject interface. I have also a factory method to create the instance of the original implementation.

If I use Eclipse I can get a stub for each method:

@Override
public R1 method(T1 p1) {
    // TODO Auto-generated method stub
        return null;
}

I need to create implementation like this:

@Override
public R1 method(T1 p1) {
    return instance.method(p1);
}

Because there are a lot of methods I used regexp with search and replace. Search for:

public ([a-z,A-Z,\.]*) ([a-z,A-Z]*)\(([a-z,A-Z]* ([a-z,A-Z]*))?\) \{\r\n([ ,\t]*)// TODO Auto-generated method stub\r\n[ ,\t]*return [0-9,a-z,A-Z]*\;

And replace with:

public \1 \2\(\3\) \{\r\n\5return instance\.\2\(\4\);

Is there a better solution?

Another problem comes with methods that take more params:

@Override
public R1 method(T1 p1, T2 p2) {
    // TODO Auto-generated method stub
    return null;
}

The only solution I found is to have a different search-replace pairs for each number of params. Is there a better solution?

Answer 1

The easisest solution would probably to just use and IDE. For example in Netbeans 7 you could write the following skeleton:

public class MyProxy implements SomeInterface {
    private SomeInterface instance;

}

Then you place your curson inside the class, hit ALT and Insert, choose “delegate method”, select all methods of the interface and click on generate.

Another, more dynamic, possibility would be to use the java.lang.reflect.Proxy class of the jdk. This allows you to define a class at runtime that implements a given interface:

public static SomeInterface create() {
    return (SomeInterface)Proxy.newProxyInstance(MyProxy.class.getClassLoader(), new Class[]{SomeInterface.class}, new InvocationHandler() {
        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
            if ("method1".equals(method.getName())) {
                // Some special logic for this method
                return null;
            } else {
                // delegate all other methods
                return method.invoke(proxy, args);
            }
        }
    });
}