invocationhandler

Here is the introduction in Oracle:

InvocationHandler is the interface implemented by the invocation handler of a proxy instance.
Each proxy instance has an associated invocation handler. When a method is invoked on a proxy instance, the method invocation is encoded and dispatched to the invoke method of its invocation handler.

Here is an example:

import java.lang.reflect.*;

public class Main {
    static void customer(ProxyInterface pi){
        pi.say();
    }
    public static void main(String[] args){
        RealObject real = new RealObject();
        ProxyInterface proxy = (ProxyInterface)Proxy.newProxyInstance(ProxyInterface.class.getClassLoader(),new Class[]{ProxyInterface.class}, new ProxyObject(real));
        customer(proxy);
    }
}


interface ProxyInterface{
    void say();
}

class RealObject implements ProxyInterface{
    public void say(){
        System.out.println("i'm talking");
    }
}

//implement InvocationHandler 
class ProxyObject implements InvocationHandler{
    private Object proxied = null;
    public ProxyObject(){

    }
    public ProxyObject(Object proxied){
        this.proxied  = proxied;
    }
    public Object invoke(Object arg0, Method arg1, Object[] arg2) throws Throwable {
        System.out.println("hello");
        return arg1.invoke(proxied, arg2);
    };
}

Here we can see the proxy class implements an InvocationHandler interface. We can use newProxyInstance to get a instance then use it as a param.