Spring Core动态代理实现代码

本篇文章小编给大家分享一下Spring Core动态代理实现代码，文章代码介绍的很详细，小编觉得挺不错的，现在分享给大家供大家参考，有需要的小伙伴们可以来看看。

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