JDK dynamic proxies provide a mechanism to create proxy instances that implement specified interfaces at runtime. Here's a basic implementation:

import java.lang.reflect.*;

interface GreetingService {
    void greet();
}

class GreetingServiceImpl implements GreetingService {
    public void greet() {
        System.out.println("Hello from service");
    }
}

class ServiceProxyHandler implements InvocationHandler {
    private Object target;
    
    public Object bind(Object target) {
        this.target = target;
        return Proxy.newProxyInstance(
            target.getClass().getClassLoader(),
            target.getClass().getInterfaces(),
            this
        );
    }
    
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("Before method execution");
        Object result = method.invoke(target, args);
        System.out.println("After method execution");
        return result;
    }
}

public class ProxyDemo {
    public static void main(String[] args) {
        GreetingService proxy = (GreetingService) new ServiceProxyHandler()
            .bind(new GreetingServiceImpl());
        proxy.greet();
    }
}

Output:

Before method execution
Hello from service
After method execution

Multiple Interface Implementation

When a target class implements multiple interfaces, the proxy can handle all of them:

interface Logger {
    void logMessage(String msg);
}

class MultiServiceImpl implements GreetingService, Logger {
    public void greet() {
        System.out.println("Greeting from service");
    }
    
    public void logMessage(String msg) {
        System.out.println("Logging: " + msg);
    }
}

public class MultiInterfaceDemo {
    public static void main(String[] args) {
        Object proxy = new ServiceProxyHandler()
            .bind(new MultiServiceImpl());
            
        ((GreetingService)proxy).greet();
        ((Logger)proxy).logMessage("Test message");
    }
}

Output:

Before method execution
Greeting from service
After method execution
Before method execution
Logging: Test message
After method execution

Key points about JDK dynamic proxies:

• The proxy implements all interfaces of the target object
• All method calls are routed through the InvocationHandler
• The proxy also handles Object class methods (equals, hashCode, toString)
• Proxy geneartion ivnolves creating a new class at runtime