代理模式
- 前言
- 一、代理模式是什么?
- 二、静态代理
- 三、动态代理
- 1.jdk动态代理(接口代理)
- 2.cglib动态代理
前言
一、代理模式是什么?
代理模式是常见的设计模式之一,顾名思义,代理模式就是代理对象具备真实对象的功能,并代替真实对象完成相应操作,并能够在操作执行的前后,对操作进行增强处理。(为真实对象提供代理,然后供其他对象通过代理访问真实对象)
二、静态代理
以租房为例,租客找房东租房,然后中间经过房屋中介,以此为背景,它的UML图如下:
可以看出房东类(RentHouse)和代理类(IntermediaryProxy)都实现了租房接口,这就是一个静态代理的前提,那就是真实类和代理类要实现同一个接口,在代理类中实现真实类的方法同时可以进行真实类方法的增强处理,在一个代理类中就可以完成对多个真实对象的注入工作。代码如下:
public interface IRentHouse {void rentHouse();
}
public class RentHouse implements IRentHouse {@Overridepublic void rentHouse() {System.out.println("实现租房");}
}
public class IntermediaryProxy implements IRentHouse {private IRentHouse iRent;public IntermediaryProxy(IRentHouse iRentHouse) {iRent=iRentHouse;}@Overridepublic void rentHouse() {System.out.println("交中介费");iRent.rentHouse();System.out.println("中介负责维修管理");}
}
//client测试类
public class TestStaticProxy {public static void main(String[] args) {//定义租房IRentHouse iRentHouse = new RentHouse();//定义中介IRentHouse intermediaryProxy = new IntermediaryProxy(iRentHouse);//中介租房intermediaryProxy.rentHouse();}
}
三、动态代理
从静态代理的代码中可以发现,静态代理的缺点显而易见,那就是当真实类的方法越来越多的时候,这样构建的代理类的代码量是非常大的,所以就引进动态代理.
动态代理允许使用一种方法的单个类(代理类)为具有任意数量方法的任意类(真实类)的多个方法调用提供服务,看到这句话,可以容易的联想到动态代理的实现与反射密不可分。
JAVA 反射机制是在运行状态中,对于任意一个类,都能够知道这个类的所有属性和方法;对于任意一个对象,都能够调用它的任意一个方法和属性;这种动态获取的信息以及动态调用对象的方法的功能称为 java 语言的反射机制。
1.jdk动态代理(接口代理)
Jdk代理涉及到java.lang.reflect包中的InvocationHandler接口和Proxy类,核心方法是
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable
jdk动态代理过程中实际上代理的是接口,是因为在创建代理实例的时候,依赖的是java.lang.reflect包中Proxy类的newProxyInstance方法,该方法的生效就恰恰需要这个参数;
public static Object newProxyInstance(ClassLoader loader,Class<?>[] interfaces,InvocationHandler h)throws IllegalArgumentException{……}
下面以案例来说明jdk动态代理的完整过程:涉及两套接口及其实现类,一个代理类,以及一个测试类
//接口1
public interface Animal {void wakeup();void sleep();
}//实现类1
public class Cat implements Animal {private String name;public Cat() {}public Cat(String name) {this.name = name;}@Overridepublic void wakeup() {System.out.println("小猫"+name+"早晨醒来啦");}@Overridepublic void sleep() {System.out.println("小猫"+name+"晚上睡觉啦");}
}//实现类2
public class Dog implements Animal {private String name;public Dog() {}public Dog(String name) {this.name = name;}@Overridepublic void wakeup() {System.out.println("小狗"+name+"早晨醒来啦");}@Overridepublic void sleep() {System.out.println("小狗"+name+"晚上睡觉啦");}
}
//接口2
public interface Person {void wakeup();void sleep();
}
//实现类1
public class Student implements Person{private String name;public Student() {}public Student(String name) {this.name = name;}@Overridepublic void wakeup() {System.out.println("学生"+name+"早晨醒来啦");}@Overridepublic void sleep() {System.out.println("学生"+name+"晚上睡觉啦");}
}
//实现类2
public class Doctor implements Person {private String name;public Doctor() {}public Doctor(String name) {this.name = name;}@Overridepublic void wakeup() {System.out.println("医生"+name+"早晨醒来啦");}@Overridepublic void sleep() {System.out.println("医生"+name+"晚上睡觉啦");}
}
//代理类
public class JDKDynamicProxy implements InvocationHandler {private Object bean;public JDKDynamicProxy(Object bean) {this.bean=bean;}@Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {String methodname=method.getName();if (methodname.equals("wakeup")){System.out.println("早安~~~");}else if(methodname.equals("sleep")){System.out.println("晚安~~~");}return method.invoke(bean,args);}
}
//测试类public class TestJDKDynamicProxy {public static void main(String[] args) {JDKDynamicProxy proxy = new JDKDynamicProxy(new Student("张三"));//创建代理实例Person student = (Person) Proxy.newProxyInstance(proxy.getClass().getClassLoader(), new Class[]{Person.class}, proxy);student.wakeup();student.sleep();proxy = new JDKDynamicProxy(new Doctor("王教授"));Person doctor = (Person) Proxy.newProxyInstance(proxy.getClass().getClassLoader(), new Class[]{Person.class}, proxy);doctor.wakeup();doctor.sleep();proxy = new JDKDynamicProxy(new Dog("旺旺"));Animal dog = (Animal) Proxy.newProxyInstance(proxy.getClass().getClassLoader(), new Class[]{Animal.class}, proxy);dog.wakeup();dog.sleep();proxy = new JDKDynamicProxy(new Cat("咪咪"));Animal cat = (Animal) Proxy.newProxyInstance(proxy.getClass().getClassLoader(), new Class[]{Animal.class}, proxy);cat.wakeup();cat.sleep();}
}
在执行过程中,为两个接口分别生成了编译以后的虚拟代理类$Proxy0.class 和 $Proxy1.class,下面以接口1的动态代理过程,讲述jdk动态代理的来龙去脉
//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//package com.sun.proxy;import com.deer.test.com.deer.vo.Person;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;public final class $Proxy0 extends Proxy implements Person {private static Method m1;private static Method m4;private static Method m2;private static Method m3;private static Method m0;public $Proxy0(InvocationHandler var1) throws {super(var1);}public final boolean equals(Object var1) throws {try {return (Boolean)super.h.invoke(this, m1, new Object[]{var1});} catch (RuntimeException | Error var3) {throw var3;} catch (Throwable var4) {throw new UndeclaredThrowableException(var4);}}public final void wakeup() throws {try {super.h.invoke(this, m4, (Object[])null);} catch (RuntimeException | Error var2) {throw var2;} catch (Throwable var3) {throw new UndeclaredThrowableException(var3);}}public final String toString() throws {try {return (String)super.h.invoke(this, m2, (Object[])null);} catch (RuntimeException | Error var2) {throw var2;} catch (Throwable var3) {throw new UndeclaredThrowableException(var3);}}public final void sleep() throws {try {super.h.invoke(this, m3, (Object[])null);} catch (RuntimeException | Error var2) {throw var2;} catch (Throwable var3) {throw new UndeclaredThrowableException(var3);}}public final int hashCode() throws {try {return (Integer)super.h.invoke(this, m0, (Object[])null);} catch (RuntimeException | Error var2) {throw var2;} catch (Throwable var3) {throw new UndeclaredThrowableException(var3);}}static {try {m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));m4 = Class.forName("com.deer.test.com.deer.vo.Person").getMethod("wakeup");m2 = Class.forName("java.lang.Object").getMethod("toString");m3 = Class.forName("com.deer.test.com.deer.vo.Person").getMethod("sleep");m0 = Class.forName("java.lang.Object").getMethod("hashCode");} catch (NoSuchMethodException var2) {throw new NoSuchMethodError(var2.getMessage());} catch (ClassNotFoundException var3) {throw new NoClassDefFoundError(var3.getMessage());}}
}
整个调用过程如下(省去本人由于自身原因走的弯路,直接说梳理结果):
从测试类中可以看出,一共创建了四个代理实例,然后每个代理实例对应接口的实现类,道理相同,这里只分析Student类的实现过程
总结对比:
1.静态代理中,代理类和真实类实现的是同一个接口,重写同样的方法;jdk动态代理中,代理类和真实类关系不大,代理类实现无侵入式的代码扩展。
2.静态代理中当接口中方法增加的时候,在代理类代码量也会增加,显然是不妥的;jdk动态代理解决了这个问题,当业务增加,代理类的代码不会增加。
3.jdk动态代理实现的是jdk自带InvocationHandler接口,实现了这个接口的类也叫拦截器类,也叫代理类。
2.cglib动态代理
从上面可以看出,jdk动态代理的前提条件是,要有接口存在,那还有许多场景是没有接口的,这个时候就需要cglib动态代理了,CGLIB(Code Generation Library)是一个基于ASM的字节码生成库,它允许我们在运行时对字节码进行修改和动态生成。CGLIB通过继承方式实现代理。
以下案例中所用到的**被代理类**和和上面jdk动态代理一样
cglib动态代理过程中生成的是实现类的子类,cglib是如何凭空创造的实现类的子类的,下面是测试代码
//所需的代理类
public class CglibProxy implements MethodInterceptor {private Enhancer enhancer=new Enhancer();private Object bean;public CglibProxy(Object bean) {this.bean = bean;}public Object getProxy(){//设置需要创建子类的类enhancer.setSuperclass(bean.getClass());enhancer.setCallback(this);return enhancer.create();}@Overridepublic Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {String methodName = method.getName();if (methodName.equals("wakeup")){System.out.println("早安~~~");}else if(methodName.equals("sleep")){System.out.println("晚安~~~");}return method.invoke(bean,objects);}
}
//测试类
public class TestCglibProxy {public static void main(String[] args) {//生成虚拟代理类的代码,本来虚拟代理子类是看不见的,//下面这句话的作用就是把执行过程中cglib增强后的class字节码文件System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "D:\\aop");CglibProxy proxy = new CglibProxy(new Student("张三"));Student student = (Student) proxy.getProxy();student.wakeup();student.sleep();proxy = new CglibProxy(new Doctor("王教授"));Doctor doctor = (Doctor) proxy.getProxy();doctor.wakeup();doctor.sleep();proxy = new CglibProxy(new Dog("旺旺"));Dog dog = (Dog) proxy.getProxy();dog.wakeup();dog.sleep();proxy = new CglibProxy(new Cat("咪咪"));Cat cat = (Cat) proxy.getProxy();cat.wakeup();cat.sleep();}
}
附上代理Cat类时候,生成的Cat的子类:
//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//
public class Cat$$EnhancerByCGLIB$$8ca2de8b extends Cat implements Factory {private boolean CGLIB$BOUND;public static Object CGLIB$FACTORY_DATA;private static final ThreadLocal CGLIB$THREAD_CALLBACKS;private static final Callback[] CGLIB$STATIC_CALLBACKS;private MethodInterceptor CGLIB$CALLBACK_0;private static Object CGLIB$CALLBACK_FILTER;private static final Method CGLIB$sleep$0$Method;private static final MethodProxy CGLIB$sleep$0$Proxy;private static final Object[] CGLIB$emptyArgs;private static final Method CGLIB$wakeup$1$Method;private static final MethodProxy CGLIB$wakeup$1$Proxy;private static final Method CGLIB$equals$2$Method;private static final MethodProxy CGLIB$equals$2$Proxy;private static final Method CGLIB$toString$3$Method;private static final MethodProxy CGLIB$toString$3$Proxy;private static final Method CGLIB$hashCode$4$Method;private static final MethodProxy CGLIB$hashCode$4$Proxy;private static final Method CGLIB$clone$5$Method;private static final MethodProxy CGLIB$clone$5$Proxy;static void CGLIB$STATICHOOK4() {CGLIB$THREAD_CALLBACKS = new ThreadLocal();CGLIB$emptyArgs = new Object[0];Class var0 = Class.forName("com.example.demo.cglibproxy.vo.Cat$$EnhancerByCGLIB$$8ca2de8b");Class var1;Method[] var10000 = ReflectUtils.findMethods(new String[]{"equals", "(Ljava/lang/Object;)Z", "toString", "()Ljava/lang/String;", "hashCode", "()I", "clone", "()Ljava/lang/Object;"}, (var1 = Class.forName("java.lang.Object")).getDeclaredMethods());CGLIB$equals$2$Method = var10000[0];CGLIB$equals$2$Proxy = MethodProxy.create(var1, var0, "(Ljava/lang/Object;)Z", "equals", "CGLIB$equals$2");CGLIB$toString$3$Method = var10000[1];CGLIB$toString$3$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/String;", "toString", "CGLIB$toString$3");CGLIB$hashCode$4$Method = var10000[2];CGLIB$hashCode$4$Proxy = MethodProxy.create(var1, var0, "()I", "hashCode", "CGLIB$hashCode$4");CGLIB$clone$5$Method = var10000[3];CGLIB$clone$5$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/Object;", "clone", "CGLIB$clone$5");var10000 = ReflectUtils.findMethods(new String[]{"sleep", "()V", "wakeup", "()V"}, (var1 = Class.forName("com.example.demo.cglibproxy.vo.Cat")).getDeclaredMethods());CGLIB$sleep$0$Method = var10000[0];CGLIB$sleep$0$Proxy = MethodProxy.create(var1, var0, "()V", "sleep", "CGLIB$sleep$0");CGLIB$wakeup$1$Method = var10000[1];CGLIB$wakeup$1$Proxy = MethodProxy.create(var1, var0, "()V", "wakeup", "CGLIB$wakeup$1");}final void CGLIB$sleep$0() {super.sleep();}public final void sleep() {MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;if (this.CGLIB$CALLBACK_0 == null) {CGLIB$BIND_CALLBACKS(this);var10000 = this.CGLIB$CALLBACK_0;}if (var10000 != null) {var10000.intercept(this, CGLIB$sleep$0$Method, CGLIB$emptyArgs, CGLIB$sleep$0$Proxy);} else {super.sleep();}}final void CGLIB$wakeup$1() {super.wakeup();}public final void wakeup() {MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;if (this.CGLIB$CALLBACK_0 == null) {CGLIB$BIND_CALLBACKS(this);var10000 = this.CGLIB$CALLBACK_0;}if (var10000 != null) {var10000.intercept(this, CGLIB$wakeup$1$Method, CGLIB$emptyArgs, CGLIB$wakeup$1$Proxy);} else {super.wakeup();}}final boolean CGLIB$equals$2(Object var1) {return super.equals(var1);}public final boolean equals(Object var1) {MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;if (this.CGLIB$CALLBACK_0 == null) {CGLIB$BIND_CALLBACKS(this);var10000 = this.CGLIB$CALLBACK_0;}if (var10000 != null) {Object var2 = var10000.intercept(this, CGLIB$equals$2$Method, new Object[]{var1}, CGLIB$equals$2$Proxy);return var2 == null ? false : (Boolean)var2;} else {return super.equals(var1);}}final String CGLIB$toString$3() {return super.toString();}public final String toString() {MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;if (this.CGLIB$CALLBACK_0 == null) {CGLIB$BIND_CALLBACKS(this);var10000 = this.CGLIB$CALLBACK_0;}return var10000 != null ? (String)var10000.intercept(this, CGLIB$toString$3$Method, CGLIB$emptyArgs, CGLIB$toString$3$Proxy) : super.toString();}final int CGLIB$hashCode$4() {return super.hashCode();}public final int hashCode() {MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;if (this.CGLIB$CALLBACK_0 == null) {CGLIB$BIND_CALLBACKS(this);var10000 = this.CGLIB$CALLBACK_0;}if (var10000 != null) {Object var1 = var10000.intercept(this, CGLIB$hashCode$4$Method, CGLIB$emptyArgs, CGLIB$hashCode$4$Proxy);return var1 == null ? 0 : ((Number)var1).intValue();} else {return super.hashCode();}}final Object CGLIB$clone$5() throws CloneNotSupportedException {return super.clone();}protected final Object clone() throws CloneNotSupportedException {MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;if (this.CGLIB$CALLBACK_0 == null) {CGLIB$BIND_CALLBACKS(this);var10000 = this.CGLIB$CALLBACK_0;}return var10000 != null ? var10000.intercept(this, CGLIB$clone$5$Method, CGLIB$emptyArgs, CGLIB$clone$5$Proxy) : super.clone();}public static MethodProxy CGLIB$findMethodProxy(Signature var0) {String var10000 = var0.toString();switch(var10000.hashCode()) {case -1385928386:if (var10000.equals("sleep()V")) {return CGLIB$sleep$0$Proxy;}break;case -508378822:if (var10000.equals("clone()Ljava/lang/Object;")) {return CGLIB$clone$5$Proxy;}break;case 391780310:if (var10000.equals("wakeup()V")) {return CGLIB$wakeup$1$Proxy;}break;case 1826985398:if (var10000.equals("equals(Ljava/lang/Object;)Z")) {return CGLIB$equals$2$Proxy;}break;case 1913648695:if (var10000.equals("toString()Ljava/lang/String;")) {return CGLIB$toString$3$Proxy;}break;case 1984935277:if (var10000.equals("hashCode()I")) {return CGLIB$hashCode$4$Proxy;}}return null;}public Cat$$EnhancerByCGLIB$$8ca2de8b() {CGLIB$BIND_CALLBACKS(this);}public Cat$$EnhancerByCGLIB$$8ca2de8b(String var1) {super(var1);CGLIB$BIND_CALLBACKS(this);}public static void CGLIB$SET_THREAD_CALLBACKS(Callback[] var0) {CGLIB$THREAD_CALLBACKS.set(var0);}public static void CGLIB$SET_STATIC_CALLBACKS(Callback[] var0) {CGLIB$STATIC_CALLBACKS = var0;}private static final void CGLIB$BIND_CALLBACKS(Object var0) {Cat$$EnhancerByCGLIB$$8ca2de8b var1 = (Cat$$EnhancerByCGLIB$$8ca2de8b)var0;if (!var1.CGLIB$BOUND) {var1.CGLIB$BOUND = true;Object var10000 = CGLIB$THREAD_CALLBACKS.get();if (var10000 == null) {var10000 = CGLIB$STATIC_CALLBACKS;if (CGLIB$STATIC_CALLBACKS == null) {return;}}var1.CGLIB$CALLBACK_0 = (MethodInterceptor)((Callback[])var10000)[0];}}public Object newInstance(Callback[] var1) {CGLIB$SET_THREAD_CALLBACKS(var1);Cat$$EnhancerByCGLIB$$8ca2de8b var10000 = new Cat$$EnhancerByCGLIB$$8ca2de8b();CGLIB$SET_THREAD_CALLBACKS((Callback[])null);return var10000;}public Object newInstance(Callback var1) {CGLIB$SET_THREAD_CALLBACKS(new Callback[]{var1});Cat$$EnhancerByCGLIB$$8ca2de8b var10000 = new Cat$$EnhancerByCGLIB$$8ca2de8b();CGLIB$SET_THREAD_CALLBACKS((Callback[])null);return var10000;}public Object newInstance(Class[] var1, Object[] var2, Callback[] var3) {CGLIB$SET_THREAD_CALLBACKS(var3);Cat$$EnhancerByCGLIB$$8ca2de8b var10000 = new Cat$$EnhancerByCGLIB$$8ca2de8b;switch(var1.length) {case 0:var10000.<init>();break;case 1:if (var1[0].getName().equals("java.lang.String")) {var10000.<init>((String)var2[0]);break;}throw new IllegalArgumentException("Constructor not found");default:throw new IllegalArgumentException("Constructor not found");}CGLIB$SET_THREAD_CALLBACKS((Callback[])null);return var10000;}public Callback getCallback(int var1) {CGLIB$BIND_CALLBACKS(this);MethodInterceptor var10000;switch(var1) {case 0:var10000 = this.CGLIB$CALLBACK_0;break;default:var10000 = null;}return var10000;}public void setCallback(int var1, Callback var2) {switch(var1) {case 0:this.CGLIB$CALLBACK_0 = (MethodInterceptor)var2;default:}}public Callback[] getCallbacks() {CGLIB$BIND_CALLBACKS(this);return new Callback[]{this.CGLIB$CALLBACK_0};}public void setCallbacks(Callback[] var1) {this.CGLIB$CALLBACK_0 = (MethodInterceptor)var1[0];}static {CGLIB$STATICHOOK4();}
}
不难发现,cglib生成的增强子类,比jdk生成的接口代理类默认多实现了clone();而创建这种子类的核心代码就是:
public Object getProxy(){//设置需要创建子类的类enhancer.setSuperclass(bean.getClass());enhancer.setCallback(this);return enhancer.create();}
该案例下,cglib的代理实现过程如下:
总结:cglib动态代理和jdk动态代理的区别显而易见,但是实现逻辑差不多,cglib代理类是通过实现MethodInterceptor,重写intercept方法,通过生成被代理类的子类来达到代理增强代码的目的;而Jdk代理是通过实现InvocationHandler,重写invoke方法,通过生成接口的代理类来达到代码增强的目的,所以jdk动态代理的实现需要接口,cglib则不需要,spring5.0以上以及springboot2.0以上默认采用cglib动态来实现AOP。后面将专门介绍AOP以及spring中是如何实现AOP的!不当之处欢迎大家批评并指正!