一、JDK的動態代理

代理模式最主要的就是有一個公共介面（Person），一個具體的類（Student），一個代理類（StudentsProxy）,代理類持有具體類的例項，代為執行具體類例項方法。

簡單實現如下：

//公共介面類
public interface Person {
    public String sayHello();
    public String eating(String name);
}
//實現類
public class Student implements Person {
    private Long id;
    private String name;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Student() {
    }

    @Override
    public String sayHello( ) {
        System.out.println(name+"-- sayHello() --");
        return name + " hello, AOP";
    }

    @Override
	public String eating(String name) {
		// TODO Auto-generated method stub
    	System.out.println(name+" is eating someThing.........");
		return null;
	}

	public void eat(String food){
        System.out.println("我正在吃：" + food);
    }
}


//實現InvocationHandler 介面的類
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;

public class StuInvocationHandler<T> implements InvocationHandler {

    private T stu;

    public StuInvocationHandler(T stu) {
        this.stu = stu;
    }

    public void doSomeThingBefore(){
        System.out.println("before...............");
    }

    public void doSomeThingAfter(){
        System.out.println("after................");
    }
    /**
     * proxy:代表動態代理物件
     * method：代表正在執行的方法
     * args：代表呼叫目標方法時傳入的實參
     */
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        doSomeThingBefore();
        Object ob = method.invoke(this.stu,args);
        doSomeThingAfter();
        return ob;
    }
}

//測試呼叫
public class ProxyTest {
    public static void main(String[] args) {
        Student stu = new Student();
        stu.setName("zhangsan");
        //建立一個與代理物件相關聯的InvocationHandler
        InvocationHandler stuHandler = new StuInvocationHandler<Person>(stu);
        //建立一個代理物件stuProxy來代理zhangsan，代理物件的每個執行方法都會替換執行Invocation中的invoke方法
        Person stuProxy = (Person) Proxy.newProxyInstance(Person.class.getClassLoader(), new Class<?>[]{Person.class}, stuHandler);
        //Student stuProxy = (Student) Proxy.newProxyInstance(Student.class.getClassLoader(), new Class<?>[]{Student.class}, stuHandler);
        //代理物件必須是介面型別 否者編譯失敗： Student is not an interface
        //代理執行上交班費的方法
        stuProxy.sayHello();
        stuProxy.eating("zhangsan");
        
    }
}