Sample Java Proxy

PersistenceServiceProxy.java

interface PersistenceService {
    Object save(Object obj);
}

class DatabasePersistenceService implements PersistenceService {
    @Override
    public Object save(Object obj) {
        //save to the database
        return null;
    }
}

public class PersistenceServiceProxy implements InvocationHandler {

    private Object obj;

    public static Object newInstance(Object obj) {
        return java.lang.reflect.Proxy.newProxyInstance(
                obj.getClass().getClassLoader(),
                obj.getClass().getInterfaces(),
                new PersistenceServiceProxy(obj));
    }

    private PersistenceServiceProxy(Object obj) {
        this.obj = obj;
    }

    public Object invoke(Object proxy, Method m, Object[] args)
            throws Throwable {
        Object result;
        try {
            System.out.println("before method " + m.getName());
            result = m.invoke(obj, args);
        } catch (InvocationTargetException e) {
            throw e.getTargetException();
        } catch (Exception e) {
            throw new RuntimeException("unexpected invocation exception: " +
                    e.getMessage());
        } finally {
            System.out.println("after method " + m.getName());
        }
        return result;
    }

    public static void main(String... args) {
        PersistenceService proxy = (PersistenceService) PersistenceServiceProxy.newInstance(new DatabasePersistenceService());
        proxy.save(new Object());
    }
}