Spring-ProxyFactory-编程知识

ProxyFactory选择cglib或jdk动态代理原理

ProxyFactory在生成代理对象之前需要决定是使用JDK动态代理还是CGLIB技术：

public class DefaultAopProxyFactory implements AopProxyFactory, Serializable {@Overridepublic AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {// 如果ProxyFactory的isOptimize为true，Spring认为cglib比jdk动态代理要快// 或者isProxyTargetClass为true，// 或者被代理对象没有实现接口，// 或者只实现了SpringProxy这个接口// 那么则利用Cglib进行动态代理，但如果被代理类是接口，或者被代理类已经是进行过JDK动态代理而生成的代理类了则只能进行JDK动态代理// 其他情况都会进行JDK动态代理，比如被代理类实现了除SpringProxy接口之外的其他接口// 是不是在GraalVM虚拟机上运行if (!NativeDetector.inNativeImage() &&(config.isOptimize() || config.isProxyTargetClass() || hasNoUserSuppliedProxyInterfaces(config))) {// config就是ProxyFactory对象Class<?> targetClass = config.getTargetClass();if (targetClass == null) {throw new AopConfigException("TargetSource cannot determine target class: " +"Either an interface or a target is required for proxy creation.");}// targetClass是接口，直接使用Jdk动态代理if (targetClass.isInterface() || Proxy.isProxyClass(targetClass)) {return new JdkDynamicAopProxy(config);}// 使用Cglibreturn new ObjenesisCglibAopProxy(config);}else {// 使用Jdk动态代理return new JdkDynamicAopProxy(config);}}/*** Determine whether the supplied {@link AdvisedSupport} has only the* {@link org.springframework.aop.SpringProxy} interface specified* (or no proxy interfaces specified at all).*/private boolean hasNoUserSuppliedProxyInterfaces(AdvisedSupport config) {Class<?>[] ifcs = config.getProxiedInterfaces();return (ifcs.length == 0 || (ifcs.length == 1 && SpringProxy.class.isAssignableFrom(ifcs[0])));}
}

代理对象创建过程

JdkDynamicAopProxy

/*** Construct a new JdkDynamicAopProxy 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 JdkDynamicAopProxy(AdvisedSupport config) throws AopConfigException {Assert.notNull(config, "AdvisedSupport must not be null");if (config.getAdvisorCount() == 0 && config.getTargetSource() == AdvisedSupport.EMPTY_TARGET_SOURCE) {throw new AopConfigException("No advisors and no TargetSource specified");}this.advised = config;// 设置JDK动态代理所要代理的接口this.proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised, true);findDefinedEqualsAndHashCodeMethods(this.proxiedInterfaces);
}// 1、在构造JdkDynamicAopProxy对象时，会先拿到被代理对象自己所实现的接口，
// 并且额外的增加SpringProxy、Advised、DecoratingProxy三个接口，组合成一个Class[]，
// 并赋值给proxiedInterfaces属性
static Class<?>[] completeProxiedInterfaces(AdvisedSupport advised, boolean decoratingProxy) {// 被代理对象自己所实现的接口Class<?>[] specifiedInterfaces = advised.getProxiedInterfaces();// 如果被代理对象没有实现接口，则判断被代理类是不是接口，或者被代理类是不是已经经过JDK动态代理之后的类从而获取想对应的接口if (specifiedInterfaces.length == 0) {// No user-specified interfaces: check whether target class is an interface.Class<?> targetClass = advised.getTargetClass();if (targetClass != null) {if (targetClass.isInterface()) {advised.setInterfaces(targetClass);}else if (Proxy.isProxyClass(targetClass)) {advised.setInterfaces(targetClass.getInterfaces());}specifiedInterfaces = advised.getProxiedInterfaces();}}// 添加三个Spring内置接口：SpringProxy、Advised、DecoratingProxyList<Class<?>> proxiedInterfaces = new ArrayList<>(specifiedInterfaces.length + 3);for (Class<?> ifc : specifiedInterfaces) {// Only non-sealed interfaces are actually eligible for JDK proxying (on JDK 17)if (isSealedMethod == null || Boolean.FALSE.equals(ReflectionUtils.invokeMethod(isSealedMethod, ifc))) {proxiedInterfaces.add(ifc);}}if (!advised.isInterfaceProxied(SpringProxy.class)) {proxiedInterfaces.add(SpringProxy.class);}if (!advised.isOpaque() && !advised.isInterfaceProxied(Advised.class)) {proxiedInterfaces.add(Advised.class);}if (decoratingProxy && !advised.isInterfaceProxied(DecoratingProxy.class)) {proxiedInterfaces.add(DecoratingProxy.class);}return ClassUtils.toClassArray(proxiedInterfaces);
}// 2、检查这些接口中是否定义了equals()、hashcode()方法
private void findDefinedEqualsAndHashCodeMethods(Class<?>[] proxiedInterfaces) {// 判断被代理的接口中是否定义了equals()、hashCode()方法，// 如果在接口中手动定义了这两个方法，则也会进行代理// 否则这两个方法是不会走代理逻辑的for (Class<?> proxiedInterface : proxiedInterfaces) {Method[] methods = proxiedInterface.getDeclaredMethods();for (Method method : methods) {if (AopUtils.isEqualsMethod(method)) {this.equalsDefined = true;}if (AopUtils.isHashCodeMethod(method)) {this.hashCodeDefined = true;}if (this.equalsDefined && this.hashCodeDefined) {return;}}}
}// 3、得到代理对象，JdkDynamicAopProxy作为InvocationHandler
// 代理对象在执行某个方法时，会进入到JdkDynamicAopProxy的invoke()方法中
public Object getProxy(@Nullable ClassLoader classLoader) {if (logger.isTraceEnabled()) {logger.trace("Creating JDK dynamic proxy: " + this.advised.getTargetSource());}// this实现了InvocationHandlerreturn Proxy.newProxyInstance(classLoader, this.proxiedInterfaces, this);
}

ObjenesisCglibAopProxy

@Override
public Object getProxy(@Nullable ClassLoader classLoader) {if (logger.isTraceEnabled()) {logger.trace("Creating CGLIB proxy: " + this.advised.getTargetSource());}try {// 被代理的类Class<?> rootClass = this.advised.getTargetClass();Assert.state(rootClass != null, "Target class must be available for creating a CGLIB proxy");Class<?> proxySuperClass = rootClass;// 0、如果被代理类本身就已经是Cglib所生成的代理类了if (rootClass.getName().contains(ClassUtils.CGLIB_CLASS_SEPARATOR)) {// 获取真正的被代理类proxySuperClass = rootClass.getSuperclass();// 获取被代理类所实现的接口Class<?>[] additionalInterfaces = rootClass.getInterfaces();for (Class<?> additionalInterface : additionalInterfaces) {this.advised.addInterface(additionalInterface);}}// Validate the class, writing log messages as necessary.validateClassIfNecessary(proxySuperClass, classLoader);// Configure CGLIB Enhancer...// 1、创建Enhancer对象Enhancer enhancer = createEnhancer();if (classLoader != null) {enhancer.setClassLoader(classLoader);if (classLoader instanceof SmartClassLoader &&((SmartClassLoader) classLoader).isClassReloadable(proxySuperClass)) {enhancer.setUseCache(false);}}// 2、被代理类，代理类的父类。proxySuperClass就是ProxyFactory.setTarget()所设置的对象的类enhancer.setSuperclass(proxySuperClass);// 3、代理类额外要实现的接口。通过ProxyFactory.addInterface()所添加的接口，// 以及SpringProxy、Advised、DecoratingProxy接口enhancer.setInterfaces(AopProxyUtils.completeProxiedInterfaces(this.advised));enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);enhancer.setStrategy(new ClassLoaderAwareGeneratorStrategy(classLoader));// 获取和被代理类所匹配的AdvisorCallback[] callbacks = getCallbacks(rootClass);Class<?>[] types = new Class<?>[callbacks.length];for (int x = 0; x < types.length; x++) {types[x] = callbacks[x].getClass();}// fixedInterceptorMap only populated at this point, after getCallbacks call aboveenhancer.setCallbackFilter(new ProxyCallbackFilter(this.advised.getConfigurationOnlyCopy(), this.fixedInterceptorMap, this.fixedInterceptorOffset));enhancer.setCallbackTypes(types);// Generate the proxy class and create a proxy instance.// 4、设置Enhancer的Callbacks为DynamicAdvisedInterceptor// 代理对象在执行某个方法时，会进入到DynamicAdvisedInterceptor的intercept()方法中return createProxyClassAndInstance(enhancer, callbacks);}catch (CodeGenerationException | IllegalArgumentException ex) {throw new AopConfigException("Could not generate CGLIB subclass of " + this.advised.getTargetClass() +": Common causes of this problem include using a final class or a non-visible class",ex);}catch (Throwable ex) {// TargetSource.getTarget() failedthrow new AopConfigException("Unexpected AOP exception", ex);}
}

代理对象执行过程

1、在使用ProxyFactory创建代理对象之前，需要往ProxyFactory先添加Advisor

2、代理对象在执行某个方法时，会把ProxyFactory中的Advisor拿出来和当前正在执行的方法进行匹配筛选

3、把和方法所匹配的Advisor适配成MethodInterceptor

4、把和当前方法匹配的MethodInterceptor链，以及被代理对象、代理对象、代理类、当前Method对象、方法参数封装为MethodInvocation对象

5、调用MethodInvocation的proceed()方法，开始执行各个MethodInterceptor以及被代理对象的对应方法

6、按顺序调用每个MethodInterceptor的invoke()方法，并且会把MethodInvocation对象传入invoke()方法

7、直到执行完最后一个MethodInterceptor，就会调用invokeJoinpoint()方法，从而执行被代理对象的当前方法

各注解对应的MethodInterceptor

@Before对应的是AspectJMethodBeforeAdvice，在进行动态代理时会把AspectJMethodBeforeAdvice转成MethodBeforeAdviceInterceptor

先执行advice对应的方法
再执行MethodInvocation的proceed()，会执行下一个Interceptor，如果没有下一个Interceptor了，会执行target对应的方法

@After对应的是AspectJAfterAdvice，直接实现了MethodInterceptor

先执行MethodInvocation的proceed()，会执行下一个Interceptor，如果没有下一个Interceptor了，会执行target对应的方法
再执行advice对应的方法

@Around对应的是AspectJAroundAdvice，直接实现了MethodInterceptor

直接执行advice对应的方法，由@Around自己决定要不要继续往后面调用

@AfterThrowing对应的是AspectJAfterThrowingAdvice，直接实现了MethodInterceptor

先执行MethodInvocation的proceed()，会执行下一个Interceptor，如果没有下一个Interceptor了，会执行target对应的方法
如果上面抛了Throwable，那么则会执行advice对应的方法

@AfterReturning对应的是AspectJAfterReturningAdvice，在进行动态代理时会把AspectJAfterReturningAdvice转成AfterReturningAdviceInterceptor

先执行MethodInvocation的proceed()，会执行下一个Interceptor，如果没有下一个Interceptor了，会执行target对应的方法
执行上面的方法后得到最终的方法的返回值
再执行advice对应的方法

AbstractAdvisorAutoProxyCreator

DefaultAdvisorAutoProxyCreator的父类是AbstractAdvisorAutoProxyCreator。 AbstractAdvisorAutoProxyCreator非常强大以及重要，只要Spring容器中存在这个类型的Bean，就相当于开启了AOP，AbstractAdvisorAutoProxyCreator实际上就是一个BeanPostProcessor，所以在创建某个Bean时，就会进入到它对应的生命周期方法中。

当某个Bean初始化后，会调用wrapIfNecessary()方法进行AOP：AbstractAdvisorAutoProxyCreator会找到所有的Advisor，然后判断当前这个Bean是否存在某个Advisor与之匹配（根据Pointcut），如果匹配就表示当前这个Bean有对应的切面逻辑，需要进行AOP，需要产生一个代理对象。