怎么实现Spring Core动态代理

本篇内容主要讲解"怎么实现Spring Core动态代理"，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习"怎么实现Spring Core动态代理"吧!

目录

• 1.设计原理

• 2.ProxyFactory (Spring-Core)

• 2.1 JdkDynamicAopProxy

• 2.2 CglibAopProxy

• 2.3 主要源码部分

1.设计原理

通过JDK的Proxy方式或者CGLIB方式生成代理对象的时候，相关的拦截器已经配置到代理对象中去了；
通过拦截器回调

JDK动态代理：代理类和目标类实现了共同的接口，用到InvocationHandler接口。(见下面代码)
CGLIB动态代理：代理类是目标类的子类，用到MethodInterceptor接口。(见下面代码)

jdk动态代理是由Java内部的反射机制来实现的；
cglib动态代理底层则是借助asm来实现的。

jdk （Proxy）

使用了Proxy类的newProxyInstance()方法来创建代理对象

final UserService target=new UserServiceImpl();        Class clazz = UserService.class;        ClassLoader loader = clazz.getClassLoader();        Object proxyInstance = Proxy.newProxyInstance(loader, new Class[]{clazz}, new InvocationHandler() {            @Override            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {                System.out.println("Before...");                Object result = method.invoke(target, args);                System.out.println("After...");                return result;            }        });        UserService service = (UserService) proxyInstance;        service.getUserInfo();

cglib

动态类对象Enhancer，它是CGLIB的核心类；Enhancer类的setSuperclass()方法来确定目标对象；setCallback()方法添加回调函数。最后通过return 语句将创建的代理类对象返回。intercept()方法会在程序执行目标方法时被调用，方法运行时会执行切面类中的增强方法（前和后）。

Enhancer enhancer=new Enhancer();        enhancer.setSuperclass(UserInfo.class);        enhancer.setCallbacks(new Callback[]{new MethodInterceptor() {            @Override            public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {                System.out.println("Before...");                Object result = methodProxy.invokeSuper(o, objects);                System.out.println("After...");                return result;            }        }});        UserInfo userInfo = (UserInfo) enhancer.create();        userInfo.test();

2.ProxyFactory (Spring-Core)

ProxyFactory在生成代理对象之前需要决定到底是使用JDK动态代理还是CGLIB技术；
getProxy() 返回 CglibAopProxy 或者 JdkDynamicAopProxy

UserService target=new UserServiceImpl();        ProxyFactory proxyFactory=new ProxyFactory();        proxyFactory.setTarget(target);        //addAdvice() 添加多个，自动形成责任链        proxyFactory.addAdvice(new AopMethodAroundAdvice());        proxyFactory.addAdvice(new AopMethodBeforeAdvice());        proxyFactory.addAdvice(new AopMethodAfterAdvice());        proxyFactory.addAdvice(new AopMethodThrowsAdvice());                //Advisor 设置具体 pointCut和  advice//        proxyFactory.addAdvisor(new AopPointcutAdvisor());        UserService userService = (UserService) proxyFactory.getProxy();        userService.getUserInfo();        userService.test();

public Object getProxy() {                return createAopProxy().getProxy();        }

2.1 JdkDynamicAopProxy

final class JdkDynamicAopProxy implements AopProxy, InvocationHandler, Serializable {        @Override        public Object getProxy() {                return getProxy(ClassUtils.getDefaultClassLoader());        }        @Override        public Object getProxy(@Nullable ClassLoader classLoader) {                if (logger.isTraceEnabled()) {                        logger.trace("Creating JDK dynamic proxy: " + this.advised.getTargetSource());                }                return Proxy.newProxyInstance(classLoader, this.proxiedInterfaces, this);        }        @Override        @Nullable        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {                                                ...省略...                        Object retVal;                        if (this.advised.exposeProxy) {                                // Make invocation available if necessary.                                oldProxy = AopContext.setCurrentProxy(proxy);                                setProxyContext = true;                        }                        // Get as late as possible to minimize the time we "own" the target,                        // in case it comes from a pool.                        target = targetSource.getTarget();                        Class targetClass = (target != null ? target.getClass() : null);                        //重点：获取此方法的拦截链                        List