JVM动态代理

https://www.zhihu.com/question/20794107

public class Main {
    public static void main(String[] args) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
        //People为接口
        //代理的对象User实现接口People
        //获得代理Class对象
        Class peopleProxyClass = Proxy.getProxyClass(People.class.getClassLoader(),People.class);
        //获得代理Class对象的构造器
        Constructor constructor = peopleProxyClass.getConstructor(InvocationHandler.class);
        //通过构造器获得代理对象
        People peopleImpl = (People)constructor.newInstance(new InvocationHandler() {
            //实现代理
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                //方法前的业务
                System.out.println("方法执行前");
                //user为代理对象
                User user = new User();
                //执行代理对象的原方法
                //通过InvocationHandler的实例调用
                Object result = method.invoke(user,args);
                //方法后的业务
                System.out.println("方法执行后");
                return result;
            }
        });
        //执行代理对象的方法
        peopleImpl.print();
        User user = new User();
        People people = (People) getProxy(user);
        people.print();
    }
    private static Object getProxy(final Object target) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
        Class peopleProxyClass = Proxy.getProxyClass(target.getClass().getClassLoader(),target.getClass().getInterfaces());
        Constructor constructor = peopleProxyClass.getConstructor(InvocationHandler.class);
        Object proxy = constructor.newInstance(new InvocationHandler() {
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                //方法前的业务
                System.out.println("方法执行前");
                //target为代理对象
                Object result = method.invoke(target,args);
                //方法后的业务
                System.out.println("方法执行后");
                return result;
            }
        });
        return proxy;
    }
    private static Object getProxy2(final Object target) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
       //使用newProxyInstance
        Object proxy = Proxy.newProxyInstance(
               target.getClass().getClassLoader(),
               target.getClass().getInterfaces(),
               new InvocationHandler() {
                   public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                       //方法前的业务
                       System.out.println("方法执行前");
                       //target为代理对象
                       Object result = method.invoke(target,args);
                       //方法后的业务
                       System.out.println("方法执行后");
                       return result;
                   }
               });
        return proxy;
    }
}