Spring AOP获取Proxy对象的代码流程

前面一篇给出了一个模拟springAOP的小例子，大家可以看到大概流程，今天我们从spring源码中分析获取Proxy对象的代码流程

 

当我们有了advice和pointcut之后，需要一个通知器来通知在哪应用切点以及一些处理动作advice。

我们会通过ProxyFactoryBean来配置我们的代理对象和方面行为，获得代理对象即靠下面的代码

public Object getObject() throws BeansException { //初始化通知器链initializeAdvisorChain();if (isSingleton()) {return getSingletonInstance();}else {if (this.targetName == null) {logger.warn("Using non-singleton proxies with singleton targets is often undesirable. " +"Enable prototype proxies by setting the 'targetName' property.");}return newPrototypeInstance();}}

 

生成单例代理对象getSingletonInstance

private synchronized Object getSingletonInstance() {if (this.singletonInstance == null) {this.targetSource = freshTargetSource();if (this.autodetectInterfaces && getProxiedInterfaces().length == 0 && !isProxyTargetClass()) {// Rely on AOP infrastructure to tell us what interfaces to proxy.Class targetClass = getTargetClass();if (targetClass == null) {throw new FactoryBeanNotInitializedException("Cannot determine target class for proxy");}setInterfaces(ClassUtils.getAllInterfacesForClass(targetClass, this.proxyClassLoader));}// Initialize the shared singleton instance.super.setFrozen(this.freezeProxy);//生成我们需要的Proxythis.singletonInstance = getProxy(createAopProxy());}return this.singletonInstance;}

 

我们接着看这个方法createAopProxy

/** * Subclasses should call this to get a new AOP proxy. They should <b>not</b> * create an AOP proxy with <code>this</code> as an argument. */protected final synchronized AopProxy createAopProxy() {if (!this.active) {activate();}return getAopProxyFactory().createAopProxy(this);}

然后进入AopProxy org.springframework.aop.framework.AopProxyFactory.createAopProxy(AdvisedSupport config)

Create an AopProxy for the given AOP configuration.

 

public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {//如果目标类不是接口，进入cglib的方法if (config.isOptimize() || config.isProxyTargetClass() || hasNoUserSuppliedProxyInterfaces(config)) {Class targetClass = config.getTargetClass();//如果没有cglib的包 抛出异常if (targetClass == null) {throw new AopConfigException("TargetSource cannot determine target class: " +"Either an interface or a target is required for proxy creation.");}if (targetClass.isInterface()) {return new JdkDynamicAopProxy(config);}if (!cglibAvailable) {throw new AopConfigException("Cannot proxy target class because CGLIB2 is not available. " +"Add CGLIB to the class path or specify proxy interfaces.");}//返回cglib类型的AopProxyreturn CglibProxyFactory.createCglibProxy(config);}else {//如果目标类为接口，返回JDK类型的AopProxyreturn new JdkDynamicAopProxy(config);}}

 

JDK类型的AopProxy的方法如下

public Object getProxy(ClassLoader classLoader) {if (logger.isDebugEnabled()) {logger.debug("Creating JDK dynamic proxy: target source is " + this.advised.getTargetSource());}Class[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised);findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);//生成需要的Proxy实例return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);}

 

 

下面为cglib类型的AopProxy方法

public static AopProxy createCglibProxy(AdvisedSupport advisedSupport) {return new Cglib2AopProxy(advisedSupport);}/** * Create a new Cglib2AopProxy for the given AOP configuration. * @param config the AOP configuration as AdvisedSupport object * @throws AopConfigException if the config is invalid. We try to throw an informative * exception in this case, rather than let a mysterious failure happen later. */public Cglib2AopProxy(AdvisedSupport config) throws AopConfigException {Assert.notNull(config, "AdvisedSupport must not be null");if (config.getAdvisors().length == 0 && config.getTargetSource() == AdvisedSupport.EMPTY_TARGET_SOURCE) {throw new AopConfigException("No advisors and no TargetSource specified");}this.advised = config;this.advisedDispatcher = new AdvisedDispatcher(this.advised);}

 

      这样用Proxy包装target之后，通过ProxyFactoryBean得到对其方法的调用就被Proxy拦截了， ProxyFactoryBean的getObject()方法得到的
实际上是一个Proxy了，我们的target对象已经被封装了。对 ProxyFactoryBean这个工厂bean而言，其生产出来的对象是封装了目标对
象的代理对象。

 

参考资料：《Spring技术内幕 - 深入解析Spring架构与设计原理》 ，spring源码。