Understanding the Difference Between JDK Dynamic Proxy and CGLib

What is the difference between JDK Dynamic Proxy and CGLib?

The Java ecosystem offers two primary mechanisms for creating dynamic proxies: JDK's built-in Dynamic Proxy and CGLib. Understanding their differences helps developers choose the right approach based on specific use cases and requirements.

// Example of JDK Dynamic Proxy
import java.lang.reflect.*;

interface SimpleInterface {
    void sayHello();
}

class SimpleClass implements SimpleInterface {
    public void sayHello() {
        System.out.println("Hello from SimpleClass!");
    }
}

class SimpleInvocationHandler implements InvocationHandler {
    private Object obj;

    public SimpleInvocationHandler(Object obj) {
        this.obj = obj;
    }

    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("Before method: " + method.getName());
        Object result = method.invoke(obj, args);
        System.out.println("After method: " + method.getName());
        return result;
    }
}

public class DynamicProxyDemo {
    public static void main(String[] args) {
        SimpleInterface obj = new SimpleClass();
        SimpleInterface proxyInstance = (SimpleInterface) Proxy.newProxyInstance(
            obj.getClass().getClassLoader(),
            new Class<?>[] { SimpleInterface.class },
            new SimpleInvocationHandler(obj)
        );
        proxyInstance.sayHello();
    }
} // This code demonstrates how to create a dynamic proxy using JDK.

Causes

• JDK Dynamic Proxy works only with interfaces, meaning you must define your behavior in an interface.
• CGLib, on the other hand, creates proxies for classes directly, allowing for more flexibility as it does not require interfaces.

Solutions

• Use JDK Dynamic Proxy when you have an interface and want a cleaner solution with less overhead.
• Opt for CGLib when your target class doesn't have an interface, or when you need to proxy the class itself.

Mistake: Confusing when to use each proxy type.

Solution: Evaluate whether you require proxying interfaces (JDK) or classes (CGLib). If your class has an interface, use JDK; otherwise, prefer CGLib.

Mistake: Not managing dependencies properly when using CGLib.

Solution: Ensure that CGLib is included in your project dependencies to avoid ClassNotFoundExceptions.