代理模式真得这么简单

代理模式的定义：为另一个对象提供一个替身或占位符以控制对这个对象的访问

代理模式类图

简单描述就是真实对象，RealSubject,和代理对象，Proxy实现同一个接口Subject,并且代理对象Proxy持有真实对象的引用

静态代理实例

GumballMachine,作为真实对象

//糖果机，拥有两个属性，位置和糖果数量
public class GumballMachine{String location;int count;public GumballMachine(String location, int count){this.location = location;]this.count = count;}public String getLocation(){return location;}public int getCount(){;return count;}
}

GumballMonitor,作为代理对象，控制对真实对象的访问

public class GumballMonitor{GumballMachine machine;public GumballMonitor(GumballMachine machine){this.machine = machine;}public void report() {System.out.println("Gumball Machine " + machine.getLocation());System.out.println("Current inventory: " + machine.getCount() + "gumballs");}
}

Main函数

public class GumballMachineTestDrive{public static void main(String args[]) {GumballMachine machine = new GumballMachine("ChangJinag", 20);GumballMonitor monitor = new GumballMonitor(machine);monitor.report();}
}

动态代理实例

java动态代理工具，在java.lang.reflect包里，使用起来其实也简单，下面用一个实例简单介绍一下java动态代理的具体用法

java动态代理类图

真实对象RealSubject,和代理对象，Proxy,实现共同接口，Proxy对象持有InvocationHanlder引用，InvocationHandler同时持有真实对象的引用。

所以对代理方法的访问，会转接到InvocationHandler类的invoke方法上，invoke方法又会主动调用RealSubect相应方法。

案例

有一个Person类，除了维护个人信息之外，还拥有一个HotOrNotRating属性(评分属性)

此属性本人不能修改，只能由他人进行修改。所以需要控制对此属性的访问。

Person和其代理共同实现的接口类

interface PersonBean{void setName(String name);void setAge(int age);void setHotOrNotRating(int HotOrNotRating);String getName();int getAge();int getHotOrNotRating();
}

Person类

class Person implements PersonBean{String name;int age;int HotOrNotRating;Person(){}Person(String name, int age, int HotOrNotRating){this.name = name; this.age = age; this.HotOrNotRating = HotOrNotRating;}public void setName(String name){this.name = name;}public void setAge(int age){this.age = age;}public void setHotOrNotRating(int HotOrNotRating){this.HotOrNotRating = HotOrNotRating;}public String getName() {return name;}public int getAge() {return age;}public int getHotOrNotRating() {return HotOrNotRating;}
}

OwnerInvocationHandler类

class OwnerInvocationHandler implements InvocationHandler{PersonBean person;public OwnerInvocationHandler(PersonBean person) {this.person = person;}public Object invoke(Object proxy, Method method, Object[]args) throws IllegalAccessException{try{if(method.getName().startsWith("set")){if(method.getName().startsWith("setHotOrNotRating")) throw new IllegalAccessException();else return method.invoke(person, args);}else return method.invoke(person,args);}catch(InvocationTargetException e) {e.printStackTrace();}return null;}
}

Main类

public class Main{//动态生成代理public static PersonBean getOwnerProxy(PersonBean person) {return (PersonBean) Proxy.newProxyInstance(person.getClass().getClassLoader(),person.getClass().getInterfaces(),new OwnerInvocationHandler(person));}public static void main(String args[]){PersonBean person = new Person("Bob", 24, 90);PersonBean ownerProxy = getOwnerProxy(person);try{ownerProxy.setHotOrNotRating(10);}catch(Exception e) {System.out.println("Owner can't modify the field of HotOrNotRating");}}
}

CGLIB代理实例

person类:与上同

实现MethodInterceptor接口，方法调用均会被intercept方法拦截

/**
sub:生成的代理对象
method:真实对象原方法
objectArr:方法参数列表
methodProxy:代理方法
**/
class MethodInterceptorImp implements MethodInterceptor{@Overridepublic Object intercept(Object sub, Method method, Object[] objectArr, MethodProxy methodProxy)throws Throwable {System.out.println("代理Start");Object object = methodProxy.invokeSuper(sub, objectArr);System.out.println("代理End");return object;}
}

Main方法

public class Main {public static void main(String args[]) {Enhancer enhancer = new Enhancer();enhancer.setSuperclass(Person.class);enhancer.setCallback(new MethodInterceptorImp());Person proxy = (Person)enhancer.create();proxy.setName("zhouyu");System.out.println(proxy.getName());}
}
//代理Start
//代理End
//代理Start
//代理End
//zhouyu

CGLIB原理解析

JDK动态代理无法代理非接口