Spring AOP如何产生代理对象
框架就是复杂的留给自己，简单的留给码农，像写hello world一样简单
早年开发Spring AOP程序时，都是xml文件配置aop（现在不流行xml了，注解@EnableAspectJAutoProxy大行其道），然后框架解析，
例如：
它这种配置是如何解析的，拦截方法怎么拿到，注入到代理，代理对象如何生成，
看下文，可以先参考我的博文bean创建过程一个Spring Bean从无到有的过程，
xml元素解析就不具体说了，感兴趣自己研究
由于我用的tag是<aop:config>,那么解析类就是ConfigBeanDefinitionParser，解析时会注册一个AspectJAwareAdvisorAutoProxyCreator，一个高高高级的BeanPostProcessor
然后解析aop:config子元素,由于方法众多，我只写了大块
if (POINTCUT.equals(localName)) {
parsePointcut(elt, parserContext);
}
else if (ADVISOR.equals(localName)) {
parseAdvisor(elt, parserContext);
}
else if (ASPECT.equals(localName)) {
parseAspect(elt, parserContext);
}
参照https://blog.csdn.net/dong19891210/article/details/105697175创建bean的createBeanInstance（产出原生对象）和initializeBean阶段,对应文件org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.java
/**
* Initialize the given bean instance, applying factory callbacks
* as well as init methods and bean post processors.
* <p>Called from {@link #createBean} for traditionally defined beans,
* and from {@link #initializeBean} for existing bean instances.
* @param beanName the bean name in the factory (for debugging purposes)
* @param bean the new bean instance we may need to initialize
* @param mbd the bean definition that the bean was created with
* (can also be {@code null}, if given an existing bean instance)
* @return the initialized bean instance (potentially wrapped)
* @see BeanNameAware
* @see BeanClassLoaderAware
* @see BeanFactoryAware
* @see #applyBeanPostProcessorsBeforeInitialization
* @see #invokeInitMethods
* @see #applyBeanPostProcessorsAfterInitialization
*/
protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
//.......略
if (mbd == null || !mbd.isSynthetic()) {
System.out.println(beanName+" AOP 6666666666666666");
wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
System.out.println(wrappedBean.getClass()+" AOP 888888888888");
}
return wrappedBean;
}
@Override
public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
throws BeansException {
Object result = existingBean;
System.out.println("对象:"+existingBean+" 的类型是："+existingBean.getClass());
List<BeanPostProcessor> beanPostProcessorList = getBeanPostProcessors();
System.out.println("BeanPostProcessor列表: "+beanPostProcessorList);
for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
//Bean初始化之后
System.out.println(beanProcessor.getClass().getName());
result = beanProcessor.postProcessAfterInitialization(result, beanName);
if (result == null) {
return result;
}
}
return result;
}在for之前输出：
calculator AOP 6666666666666666
对象:spring.aop.CalculatorImp@906d29b 的类型是：class spring.aop.CalculatorImp
BeanPostProcessor列表: [org.springframework.context.support.ApplicationContextAwareProcessor@49d3c823, org.springframework.context.support.PostProcessorRegistrationDelegate$BeanPostProcessorChecker@436bc36, org.springframework.context.annotation.ConfigurationClassPostProcessor$ImportAwareBeanPostProcessor@3b8f0a79, org.springframework.context.annotation.ConfigurationClassPostProcessor$EnhancedConfigurationBeanPostProcessor@71e693fa, proxyTargetClass=false; optimize=false; opaque=false; exposeProxy=false; frozen=false, org.springframework.context.annotation.CommonAnnotationBeanPostProcessor@4f6f416f, org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor@409c54f, org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor@3e74829, org.springframework.context.support.PostProcessorRegistrationDelegate$ApplicationListenerDetector@5fe1ce85]
获取所有的BeanPostProcessor，
进入for阶段后，留意一个org.springframework.aop.aspectj.autoproxy.AspectJAwareAdvisorAutoProxyCreator 的处理
处理方式可以细看，由于代码超多，只展示大方面的代码
还记得上面说过的注册的一个bean：AspectJAwareAdvisorAutoProxyCreator，它继承自org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator.postProcessAfterInitialization(Object bean, String beanName) throws BeansException
/**
* Create a proxy with the configured interceptors if the bean is
* identified as one to proxy by the subclass.
* @see #getAdvicesAndAdvisorsForBean
*/
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if (bean != null) {
Object cacheKey = getCacheKey(bean.getClass(), beanName);
if (!this.earlyProxyReferences.contains(cacheKey)) {
//
return wrapIfNecessary(bean, beanName, cacheKey);
}
}
return bean;
}
/**
* Wrap the given bean if necessary, i.e. if it is eligible for being proxied.
* @param bean the raw bean instance
* @param beanName the name of the bean
* @param cacheKey the cache key for metadata access
* @return a proxy wrapping the bean, or the raw bean instance as-is
*/
protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
//。。。。。略
// Create proxy if we have advice.预备创建代理对象，拿到拦截方法
Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
if (specificInterceptors != DO_NOT_PROXY) {
System.out.println("org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator.postProcessAfterInitialization(Object bean, String beanName) ");
this.advisedBeans.put(cacheKey, Boolean.TRUE);
//spring aop产生“代理对象”的地方
Object proxy = createProxy(
bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));
this.proxyTypes.put(cacheKey, proxy.getClass());
return proxy;
}
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}
在创建代理对象前，会拿到通知或拦截方法
1. 拿拦截方式org.springframework.aop.framework.autoproxy.AbstractAdvisorAutoProxyCreator.getAdvicesAndAdvisorsForBean(Class<?> beanClass, String beanName, TargetSource targetSource)
2. 创建代理 Object org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator.createProxy(Class<?> beanClass, String beanName, Object[] specificInterceptors, TargetSource targetSource)
/**
* Create an AOP proxy for the given bean.
* @param beanClass the class of the bean
* @param beanName the name of the bean
* @param specificInterceptors the set of interceptors that is
* specific to this bean (may be empty, but not null)
* @param targetSource the TargetSource for the proxy,
* already pre-configured to access the bean
* @return the AOP proxy for the bean
* @see #buildAdvisors
*/
protected Object createProxy(
Class<?> beanClass, String beanName, Object[] specificInterceptors, TargetSource targetSource) {
if (this.beanFactory instanceof ConfigurableListableBeanFactory) {
AutoProxyUtils.exposeTargetClass((ConfigurableListableBeanFactory) this.beanFactory, beanName, beanClass);
}
//开始准备原料
ProxyFactory proxyFactory = new ProxyFactory();
proxyFactory.copyFrom(this);
if (!proxyFactory.isProxyTargetClass()) {
if (shouldProxyTargetClass(beanClass, beanName)) {
proxyFactory.setProxyTargetClass(true);
}
else {
evaluateProxyInterfaces(beanClass, proxyFactory);
}
}
//很重要
Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
for (Advisor advisor : advisors) {
proxyFactory.addAdvisor(advisor);
}
proxyFactory.setTargetSource(targetSource);
customizeProxyFactory(proxyFactory);
proxyFactory.setFrozen(this.freezeProxy);
if (advisorsPreFiltered()) {
proxyFactory.setPreFiltered(true);
}
//创建代理
return proxyFactory.getProxy(getProxyClassLoader());
}
文件org.springframework.aop.framework.proxyFactory.java
/**
* Create a new proxy according to the settings in this factory.
* <p>Can be called repeatedly. Effect will vary if we've added
* or removed interfaces. Can add and remove interceptors.
* <p>Uses the given class loader (if necessary for proxy creation).
* @param classLoader the class loader to create the proxy with
* (or {@code null} for the low-level proxy facility's default)
* @return the proxy object
*/
public Object getProxy(ClassLoader classLoader) {
return createAopProxy().getProxy(classLoader);
}
public class ProxyCreatorSupport extends AdvisedSupport {
//。。。略
/**
* Create a new ProxyCreatorSupport instance.
*/
public ProxyCreatorSupport() {
this.aopProxyFactory = new DefaultAopProxyFactory();
}
/**
* Return the AopProxyFactory that this ProxyConfig uses.
*/
public AopProxyFactory getAopProxyFactory() {
return this.aopProxyFactory;
}
/**
* Subclasses should call this to get a new AOP proxy. They should <b>not</b>
* create an AOP proxy with {@code this} as an argument.
*/
protected final synchronized AopProxy createAopProxy() {
if (!this.active) {
activate();
}
return getAopProxyFactory().createAopProxy(this);
}
}
public class DefaultAopProxyFactory implements AopProxyFactory, Serializable {
@Override
public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
if (config.isOptimize() || config.isProxyTargetClass() || hasNoUserSuppliedProxyInterfaces(config)) {
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.");
}
//如果targetClass是接口，则使用JDK生成代理proxy
if (targetClass.isInterface() || Proxy.isProxyClass(targetClass)) {
return new JdkDynamicAopProxy(config);
}
//若不是接口，则使用cglib生成代理类proxy
return new ObjenesisCglibAopProxy(config);
}
else {
return new JdkDynamicAopProxy(config);
}
}
}由于我用的是接口，那么代理实现类是JdkDynamicAopProxy.java
/**
* JDK-based {@link AopProxy} implementation for the Spring AOP framework,
* based on JDK {@link java.lang.reflect.Proxy dynamic proxies}.
*
* <p>Creates a dynamic proxy, implementing the interfaces exposed by
* the AopProxy. Dynamic proxies <i>cannot</i> be used to proxy methods
* defined in classes, rather than interfaces.
*
* <p>Objects of this type should be obtained through proxy factories,
* configured by an {@link AdvisedSupport} class. This class is internal
* to Spring's AOP framework and need not be used directly by client code.
*
* <p>Proxies created using this class will be thread-safe if the
* underlying (target) class is thread-safe.
*
* <p>Proxies are serializable so long as all Advisors (including Advices
* and Pointcuts) and the TargetSource are serializable.
*
* @author Rod Johnson
* @author Juergen Hoeller
* @author Rob Harrop
* @author Dave Syer
* @see java.lang.reflect.Proxy
* @see AdvisedSupport
* @see ProxyFactory
*/
final class JdkDynamicAopProxy implements AopProxy, InvocationHandler, Serializable {
/** Config used to configure this proxy */
private final AdvisedSupport advised;
/**
* 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.getAdvisors().length == 0 && config.getTargetSource() == AdvisedSupport.EMPTY_TARGET_SOURCE) {
throw new AopConfigException("No advisors and no TargetSource specified");
}
this.advised = config;
}
@Override
public Object getProxy() {
return getProxy(ClassUtils.getDefaultClassLoader());
}
@Override
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, true);
findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);
//jdk自带的工具
return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
}
/**
* Implementation of {@code InvocationHandler.invoke}.
* <p>Callers will see exactly the exception thrown by the target,
* unless a hook method throws an exception.
*/
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
MethodInvocation invocation;
Object oldProxy = null;
boolean setProxyContext = false;
TargetSource targetSource = this.advised.targetSource;
Class<?> targetClass = null;
Object target = null;
try {
if (!this.equalsDefined && AopUtils.isEqualsMethod(method)) {
// The target does not implement the equals(Object) method itself.
return equals(args[0]);
}
else if (!this.hashCodeDefined && AopUtils.isHashCodeMethod(method)) {
// The target does not implement the hashCode() method itself.
return hashCode();
}
else if (method.getDeclaringClass() == DecoratingProxy.class) {
// There is only getDecoratedClass() declared -> dispatch to proxy config.
return AopProxyUtils.ultimateTargetClass(this.advised);
}
else if (!this.advised.opaque && method.getDeclaringClass().isInterface() &&
method.getDeclaringClass().isAssignableFrom(Advised.class)) {
// Service invocations on ProxyConfig with the proxy config...
return AopUtils.invokeJoinpointUsingReflection(this.advised, method, args);
}
Object retVal;
if (this.advised.exposeProxy) {
// Make invocation available if necessary.
oldProxy = AopContext.setCurrentProxy(proxy);
setProxyContext = true;
}
// May be null. Get as late as possible to minimize the time we "own" the target,
// in case it comes from a pool.
//得到目标对象
target = targetSource.getTarget();
if (target != null) {
targetClass = target.getClass();
}
// Get the interception chain for this method.
// 得到定义好的拦截器链
List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
// Check whether we have any advice. If we don't, we can fallback on direct
// reflective invocation of the target, and avoid creating a MethodInvocation.
if (chain.isEmpty()) {
// We can skip creating a MethodInvocation: just invoke the target directly
// Note that the final invoker must be an InvokerInterceptor so we know it does
// nothing but a reflective operation on the target, and no hot swapping or fancy proxying.
Object[] argsToUse = AopProxyUtils.adaptArgumentsIfNecessary(method, args);
retVal = AopUtils.invokeJoinpointUsingReflection(target, method, argsToUse);
}
else {
// We need to create a method invocation...
/*
* 如果有拦截器的定义，那么需要调用拦截器后才能调用目标对象的相应方法
*
*/
invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain);
// Proceed to the joinpoint through the interceptor chain.
//
retVal = invocation.proceed();
}
// Massage return value if necessary.
Class<?> returnType = method.getReturnType();
if (retVal != null && retVal == target && returnType.isInstance(proxy) &&
!RawTargetAccess.class.isAssignableFrom(method.getDeclaringClass())) {
// Special case: it returned "this" and the return type of the method
// is type-compatible. Note that we can't help if the target sets
// a reference to itself in another returned object.
retVal = proxy;
}
else if (retVal == null && returnType != Void.TYPE && returnType.isPrimitive()) {
throw new AopInvocationException(
"Null return value from advice does not match primitive return type for: " + method);
}
return retVal;
}
finally {
if (target != null && !targetSource.isStatic()) {
// Must have come from TargetSource.
targetSource.releaseTarget(target);
}
if (setProxyContext) {
// Restore old proxy.
AopContext.setCurrentProxy(oldProxy);
}
}
}
此时已是代理对象
然后一层层返回：
代理对象执行业务方法，顺便加些其他操作
总结：Spring AOP的处理由它AspectJAwareAdvisorAutoProxyCreator对bean的处理，还是对bean的生命周期的把控，在哪个阶段生成，initializeBean阶段，然后再去看怎么生成的代理对象，需要什么原材料（拦截器，通知，切面，切入点等），哪种方式（两种方式）
好了，细节慢慢深入，相信吗，Spring aop为创建代理对象，方法嵌套调用上百个，还有不少新概念，不过还好，对于开发人员用起aop来像helloword一样简单。
附图两张：
参考：
0. https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#xsd-schemas-aop
1. https://www.springframework.org/schema/aop/spring-aop.xsd
3. https://github.com/seaswalker/spring-analysis/blob/master/note/spring-aop.md
4. Spring 框架的设计理念与设计模式分析 https://www.ibm.com/developerworks/cn/java/j-lo-spring-principle/index.html
5. Understanding Spring AOP https://www.codejava.net/frameworks/spring/understanding-spring-aop
6. Spring 源码学习(八) AOP 使用和实现原理
http://www.justdojava.com/2019/07/17/spring-analysis-note-8/
7. Spring AOP 源码初窥（三）扫描Advice与Bean匹配 https://segmentfault.com/a/1190000016054658
8. Spring AOP 使用介绍，从前世到今生 https://www.javadoop.com/post/spring-aop-intro
9. spring源码解析之AOP原理 https://www.cnblogs.com/liuyk-code/p/9886033.html
