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public interface HelloWorld {
  public void sayHelloWorld();
}
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public class HelloWorldImpl implements HelloWorld {

  @Override
  public void sayHelloWorld() {
    System.out.println(">>>>>HelloWorld!<<<<<")
  }
}

动态代理的思路:

  1. 建立代理对象和真实对象之间的关系: bind;
  2. 实现代理逻辑: invoke;

实现代理逻辑类必须实现java.lang.reflect.InvocationHandler接口;

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public class JdkProxyExample implements InvocationHandler {

  // real object
  private Object target = null;

  /*
    relation: proxy object -> true object
    @param target: true object
    @return proxy object
  */
  public Object bind(Object target) {
    this.target = target;
    return Proxy.newProxyInstance(target.getClass().getClassLoader(), 
      target.getClass().getInterfaces(), this);
  }

  /*
    proxy method logics
    @param proxy: proxy object
    @param method: current invoked method
    @param args: current method args
  */
  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    System.out.println("proxy logics method");
    System.out.println("setUp service before true object");
    Object obj = method.invoke(target, args); // <=> sayHelloWorld
    System.out.println("tearDown service after true object");
    return obj;
  }
}

测试JDK动态代理:

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public void testJdkProxy() {
  JdkProxyExample jdk = new JdkProxyExample();
  HelloWorld proxy = (HelloWorld) jdk.bind(new HelloWorldImpl());
  proxy.sayHelloWorld();
}

Output:

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proxy logics method
setUp service before true object
>>>>>HelloWorld!<<<<<
tearDown service after true object