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Reflect — 4 Proxy

import java.lang.reflect.InvocationHandler; import java.lang.reflect.Method; public class LoggingHandler implements InvocationHandler private final Object target; // real object

@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; 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

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. @Override public void updateUser(int userId

| Feature | JDK Proxy | CGLIB | Byte Buddy | |---------|-----------|-------|-------------| | | Interfaces only | Concrete classes | Both | | Implementation | Reflection | Subclassing (bytecode) | Bytecode generation | | Performance | Medium | High | Highest | | Complexity | Low | Medium | High | | Modern use | Spring AOP (default) | Spring (fallback) | Mocking frameworks |

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.