public interface InvocationHandler public Object invoke(Object proxy, Method method, Object[] args) throws Throwable;
In the world of Java development, few tools are as powerful—and as misunderstood—as the Proxy class found in the java.lang.reflect package. When developers search for the term "reflect 4 proxy" (often a shorthand for "Reflect for Proxy" or a mistype of reflect4proxy ), they are typically looking to understand one core question: How do I use reflection to create, manipulate, or debug dynamic proxies?
import java.lang.reflect.Proxy; public class Main public static void main(String[] args) RealUserService realService = new RealUserService(); reflect 4 proxy
public class RealUserService implements UserService @Override public String getUserName(int userId) return "User_" + userId; @Override public void updateUser(int userId, String newName) System.out.println("Updated user " + userId + " to " + newName);
import java.lang.reflect.InvocationHandler; import java.lang.reflect.Method; public class LoggingHandler implements InvocationHandler private final Object target; // real object Enhancer enhancer = new Enhancer(); enhancer
Whether you are building aspect-oriented programming (AOP) frameworks, mocking libraries (like Mockito), or intercepting method calls for logging and security, the reflect 4 proxy mechanism is your gateway to runtime metaprogramming.
Enhancer enhancer = new Enhancer(); enhancer.setSuperclass(RealUserService.class); enhancer.setCallback(new MethodInterceptor() public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable // interceptor logic return proxy.invokeSuper(obj, args); ); RealUserService proxy = (RealUserService) enhancer.create(); The reflect 4 proxy mechanism remains a cornerstone of Java’s dynamic capabilities. Although newer versions of Java introduced features like dynamic proxies via MethodHandles (more lightweight) and inline classes (Project Valhalla), java.lang.reflect.Proxy is still widely used because it is simple, standardized, and deeply integrated into major frameworks. Enhancer enhancer = new Enhancer()
@Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable // Log before execution System.out.println("[LOG] Calling: " + method.getName()); if (args != null) for (int i = 0; i < args.length; i++) System.out.println("[LOG] Arg " + i + ": " + args[i]); // Invoke the real method via reflection Object result = method.invoke(target, args); // Log after execution System.out.println("[LOG] Returned: " + result); return result;