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.

Object invoke(Object proxy, Method method, Object[] args) throws Throwable

Proxy provides static methods for creating dynamic proxy classes and instances, and it is also the superclass of all dynamic proxy classes created by those methods.

public static Object newProxyInstance(ClassLoader loader, Class<?>[] interfaces, 
 InvocationHandler h) throws IllegalArgumentException

Returns an instance of a proxy class for the specified interfaces that dispatches method
 invocations to the specified invocation handler.

loader:一個(gè)ClassLoader對(duì)象，定義了由哪個(gè)ClassLoader對(duì)象來(lái)對(duì)生成的代理對(duì)象進(jìn)行加載
interfaces:一個(gè)Interface對(duì)象的數(shù)組，表示的是我將要給我需要代理的對(duì)象提供一組什么接口，如果我提供了一組接口給它，那么這個(gè)代理對(duì)象就宣稱(chēng)實(shí)現(xiàn)了該接口(多態(tài))，這樣我就能調(diào)用這組接口中的方法了
h:一個(gè)InvocationHandler對(duì)象，表示的是當(dāng)我這個(gè)動(dòng)態(tài)代理對(duì)象在調(diào)用方法的時(shí)候，會(huì)關(guān)聯(lián)到哪一個(gè)InvocationHandler對(duì)象上

public interface Subject
{
  public void rent();

  public void hello(String str);
}

public class RealSubject implements Subject
{
  @Override
  public void rent()
  {
    System.out.println("I want to rent my house");
  }

  @Override
  public void hello(String str)
  {
    System.out.println("hello: " + str);
  }
}

public class DynamicProxy implements InvocationHandler
{
  //　這個(gè)就是我們要代理的真實(shí)對(duì)象
  private Object subject;

  //  構(gòu)造方法，給我們要代理的真實(shí)對(duì)象賦初值
  public DynamicProxy(Object subject)
  {
    this.subject = subject;
  }

  @Override
  public Object invoke(Object object, Method method, Object[] args)
      throws Throwable
  {
    //　　在代理真實(shí)對(duì)象前我們可以添加一些自己的操作
    System.out.println("before rent house");

    System.out.println("Method:" + method);

    //  當(dāng)代理對(duì)象調(diào)用真實(shí)對(duì)象的方法時(shí)，其會(huì)自動(dòng)的跳轉(zhuǎn)到代理對(duì)象關(guān)聯(lián)的handler對(duì)象的invoke方法來(lái)進(jìn)行調(diào)用
    method.invoke(subject, args);

    //　　在代理真實(shí)對(duì)象后我們也可以添加一些自己的操作
    System.out.println("after rent house");

    return null;
  }

}

public class Client
{
  public static void main(String[] args)
  {
    //  我們要代理的真實(shí)對(duì)象
    Subject realSubject = new RealSubject();

    //  我們要代理哪個(gè)真實(shí)對(duì)象，就將該對(duì)象傳進(jìn)去，最后是通過(guò)該真實(shí)對(duì)象來(lái)調(diào)用其方法的
    InvocationHandler handler = new DynamicProxy(realSubject);

    /*
     * 通過(guò)Proxy的newProxyInstance方法來(lái)創(chuàng)建我們的代理對(duì)象，我們來(lái)看看其三個(gè)參數(shù)
     * 第一個(gè)參數(shù) handler.getClass().getClassLoader() ，我們這里使用handler這個(gè)類(lèi)的ClassLoader對(duì)象來(lái)加載我們的代理對(duì)象
     * 第二個(gè)參數(shù)realSubject.getClass().getInterfaces()，我們這里為代理對(duì)象提供的接口是真實(shí)對(duì)象所實(shí)行的接口，表示我要代理的是該真實(shí)對(duì)象，這樣我就能調(diào)用這組接口中的方法了
     * 第三個(gè)參數(shù)handler， 我們這里將這個(gè)代理對(duì)象關(guān)聯(lián)到了上方的 InvocationHandler 這個(gè)對(duì)象上
     */
    Subject subject = (Subject)Proxy.newProxyInstance(handler.getClass().getClassLoader(), realSubject
        .getClass().getInterfaces(), handler);

    System.out.println(subject.getClass().getName());
    subject.rent();
    subject.hello("world");
  }
}

$Proxy0

before rent house
Method:public abstract void com.xiaoluo.dynamicproxy.Subject.rent()
I want to rent my house
after rent house

before rent house
Method:public abstract void com.xiaoluo.dynamicproxy.Subject.hello(java.lang.String)
hello: world
after rent house

Subject subject = (Subject)Proxy.newProxyInstance(handler.getClass().getClassLoader(), realSubject
        .getClass().getInterfaces(), handler);

subject.rent();
subject.hello(“world”);

public Object invoke(Object object, Method method, Object[] args)
      throws Throwable
  {
    //　　在代理真實(shí)對(duì)象前我們可以添加一些自己的操作
    System.out.println("before rent house");

    System.out.println("Method:" + method);

    //  當(dāng)代理對(duì)象調(diào)用真實(shí)對(duì)象的方法時(shí)，其會(huì)自動(dòng)的跳轉(zhuǎn)到代理對(duì)象關(guān)聯(lián)的handler對(duì)象的invoke方法來(lái)進(jìn)行調(diào)用
    method.invoke(subject, args);

    //　　在代理真實(shí)對(duì)象后我們也可以添加一些自己的操作
    System.out.println("after rent house");

    return null;
  }

public abstract void com.xiaoluo.dynamicproxy.Subject.rent()

public abstract void com.xiaoluo.dynamicproxy.Subject.hello(java.lang.String)