Design Patterns in Java - Proxy Pattern

Proxy Pattern

• Act as an interface for something else
• Interface based

• Create an interface

public interface TwitterService {

    

    public String getTimeline();

}

• Create the implementation(s)

public class TwitterServiceStub implements TwitterService {

    @Override

    public String getTimeline() {

        return "Printing Timeline --...";

    }

}

• Create the Proxy
• that implements InvocationHandler that works by reflection

public class SecurityProxy implements InvocationHandler {

    Object obj;

    private SecurityProxy(Object obj) {

        this.obj = obj;

    }

    public static Object newInstance(Object obj) {

        return java.lang.reflect.Proxy.newProxyInstance(obj.getClass().

                getClassLoader(), obj.getClass().getInterfaces(), new SecurityProxy(obj));

    }

    @Override

    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

        Object result;

        try {

• You can add security adding
• if( method.getName.contains (" remove"  )){
•     //... don't performe an action
• }

            result = method.invoke(obj, args);

        } catch (InvocationTargetException e) {

            throw e.getTargetException();

        } catch (Exception e) {

            throw new RuntimeException("Unexpected expection: " +  e.getMessage());

        }

        

        return result;

    }

}