24、Spring源码分析 - 24-基于注解@Aspect的AOP实现
1、AnnotationAwareAspectJAutoProxyCreator注册过程
Spring应用如果想开启基于注解形式的AOP代理，只需要在@Configuration类上加入@EnableAspectJAutoProxy，因为EnableAspectJAutoProxy上有@Import(AspectJAutoProxyRegistrar.class)，就可以在bean加载阶段调用AspectJAutoProxyRegistrar.registerBeanDefinitions()方法，具体原理请看《ConfigurationClassPostProcessor原理》。
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(AspectJAutoProxyRegistrar.class)
public @interface EnableAspectJAutoProxy {
/**
* Indicate whether subclass-based (CGLIB) proxies are to be created as opposed
* to standard Java interface-based proxies. The default is {@code false}.
*/
boolean proxyTargetClass() default false;
/**
* Indicate that the proxy should be exposed by the AOP framework as a {@code ThreadLocal}
* for retrieval via the {@link org.springframework.aop.framework.AopContext} class.
* Off by default, i.e. no guarantees that {@code AopContext} access will work.
* @since 4.3.1
*/
boolean exposeProxy() default false;
}
AspectJAutoProxyRegistrar.registerBeanDefinitions()方法内部会注册一个bean name为org.springframework.aop.config.internalAutoProxyCreator的AnnotationAwareAspectJAutoProxyCreator用于解析@Aspect。
class AspectJAutoProxyRegistrar implements ImportBeanDefinitionRegistrar {
/**
* Register, escalate, and configure the AspectJ auto proxy creator based on the value
* of the @{@link EnableAspectJAutoProxy#proxyTargetClass()} attribute on the importing
* {@code @Configuration} class.
*/
@Override
public void registerBeanDefinitions(
AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
//注册bean name为org.springframework.aop.config.internalAutoProxyCreator的AnnotationAwareAspectJAutoProxyCreator
AopConfigUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(registry);
AnnotationAttributes enableAspectJAutoProxy =
AnnotationConfigUtils.attributesFor(importingClassMetadata, EnableAspectJAutoProxy.class);
if (enableAspectJAutoProxy != null) {
//如果@EnableAspectJAutoProxy的proxyTargetClass是true代表使用cglib代理目标类
//会为AnnotationAwareAspectJAutoProxyCreator添加一个属性
//definition.getPropertyValues().add("proxyTargetClass", Boolean.TRUE);
if (enableAspectJAutoProxy.getBoolean("proxyTargetClass")) {
AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
}
//definition.getPropertyValues().add("exposeProxy", Boolean.TRUE);
if (enableAspectJAutoProxy.getBoolean("exposeProxy")) {
AopConfigUtils.forceAutoProxyCreatorToExposeProxy(registry);
}
}
}
}
2、原理
首先看下AnnotationAwareAspectJAutoProxyCreator继承结构。
AnnotationAwareAspectJAutoProxyCreator通过继承AbstractAutoProxyCreator实现了BeanPostProcessor接口，postProcessAfterInitialization()方法会判断当前bean是否可以当做代理对象，如果可以则使用代理对象替换原来的bean。
@Override
public Object postProcessAfterInitialization(@Nullable Object bean, String beanName) {
if (bean != null) {
//bean name或class
Object cacheKey = getCacheKey(bean.getClass(), beanName);
if (!this.earlyProxyReferences.contains(cacheKey)) {
//bean符合代理对象的条件则包装成代理对象返回
return wrapIfNecessary(bean, beanName, cacheKey);
}
}
return bean;
}
//bean符合代理对象的条件则包装成代理对象返回
protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
if (StringUtils.hasLength(beanName) && this.targetSourcedBeans.contains(beanName)) {
return bean;
}
//不符合代理对象的也会缓存，避免重复调用此方法重新计算
if (Boolean.FALSE.equals(this.advisedBeans.get(cacheKey))) {
return bean;
}
//此方法是protected，判断bean是否可以作为拦截器，拦截器不需要被代理，
//是否是Advice、Pointcut、Advisor、AopInfrastructureBean之一，
//AnnotationAwareAspectJAutoProxyCreator实现的具体行为还包括类有@Aspect注解并且不是被Ajc编译的
if (isInfrastructureClass(bean.getClass()) || shouldSkip(bean.getClass(), beanName)) {
this.advisedBeans.put(cacheKey, Boolean.FALSE);
return bean;
}
// Create proxy if we have advice.
//取得用户定义的拦截器
Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
if (specificInterceptors != DO_NOT_PROXY) {
this.advisedBeans.put(cacheKey, Boolean.TRUE);
//使用ProxyFactory创建代理对象
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;
}
上面代码要创建一个代理对象的核心就是要得到我们定义的拦截器， 然后createProxy()方法内部使用ProxyFactory创建代理对象，使用ProxyFactory与ProxyFactoryBean原理相同可以参考/zhuanlan/j2ee/spring/7/22.html。
下面就具体看一下AbstractAdvisorAutoProxyCreator的getAdvicesAndAdvisorsForBean()方法如何取得通知器数组了。
@Override
@Nullable
protected Object[] getAdvicesAndAdvisorsForBean(
Class<?> beanClass, String beanName, @Nullable TargetSource targetSource) {
List<Advisor> advisors = findEligibleAdvisors(beanClass, beanName);
if (advisors.isEmpty()) {
return DO_NOT_PROXY;
}
return advisors.toArray();
}
//找到所有适合自动代理这个类的通知器
protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
//找出容器中所有的通知器
List<Advisor> candidateAdvisors = findCandidateAdvisors();
//从所有的通知器中找出可以应用到此bean的通知器
List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
//在使用AspectJ表达式切入点在通知链的开头添加ExposeInvocationInterceptor
extendAdvisors(eligibleAdvisors);
if (!eligibleAdvisors.isEmpty()) {
eligibleAdvisors = sortAdvisors(eligibleAdvisors);
}
return eligibleAdvisors;
}
AnnotationAwareAspectJAutoProxyCreator重写了findCandidateAdvisors()方法，首先调用父类AbstractAdvisorAutoProxyCreator的findCandidateAdvisors()方法获得一批通知器，然后使用aspectJAdvisorsBuilder在获得一批通知器。
@Override
protected List<Advisor> findCandidateAdvisors() {
// Add all the Spring advisors found according to superclass rules.
List<Advisor> advisors = super.findCandidateAdvisors();
// Build Advisors for all AspectJ aspects in the bean factory.
if (this.aspectJAdvisorsBuilder != null) {
advisors.addAll(this.aspectJAdvisorsBuilder.buildAspectJAdvisors());
}
return advisors;
}
AbstractAdvisorAutoProxyCreator的findCandidateAdvisors()方法内部使用一个BeanFactoryAdvisorRetrievalHelper取得容器内所有的通知器，这个BeanFactoryAdvisorRetrievalHelper是在setBeanFactory()方法被调用的时候实例化的。
@Override
public void setBeanFactory(BeanFactory beanFactory) {
super.setBeanFactory(beanFactory);
if (!(beanFactory instanceof ConfigurableListableBeanFactory)) {
throw new IllegalArgumentException(
"AdvisorAutoProxyCreator requires a ConfigurableListableBeanFactory: " + beanFactory);
}
initBeanFactory((ConfigurableListableBeanFactory) beanFactory);
}
protected void initBeanFactory(ConfigurableListableBeanFactory beanFactory) {
this.advisorRetrievalHelper = new BeanFactoryAdvisorRetrievalHelperAdapter(beanFactory);
}
protected List<Advisor> findCandidateAdvisors() {
Assert.state(this.advisorRetrievalHelper != null, "No BeanFactoryAdvisorRetrievalHelper available");
return this.advisorRetrievalHelper.findAdvisorBeans();
}
BeanFactoryAdvisorRetrievalHelperAdapter是AbstractAdvisorAutoProxyCreator的内部类继承了BeanFactoryAdvisorRetrievalHelper拥有了findAdvisorBeans()的能力。
public List<Advisor> findAdvisorBeans() {
// Determine list of advisor bean names, if not cached already.
String[] advisorNames = this.cachedAdvisorBeanNames;
if (advisorNames == null) {
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let the auto-proxy creator apply to them!
advisorNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
this.beanFactory, Advisor.class, true, false);
this.cachedAdvisorBeanNames = advisorNames;
}
if (advisorNames.length == 0) {
return new ArrayList<>();
}
List<Advisor> advisors = new ArrayList<>();
//advisorNames是容器中所有Advisor类型的bean name
for (String name : advisorNames) {
//直接返回的是true
if (isEligibleBean(name)) {
//忽略当前正在创建的bean
if (this.beanFactory.isCurrentlyInCreation(name)) {
if (logger.isTraceEnabled()) {
logger.trace("Skipping currently created advisor '" + name + "'");
}
}
else {
try {
advisors.add(this.beanFactory.getBean(name, Advisor.class));
}
catch (BeanCreationException ex) {
Throwable rootCause = ex.getMostSpecificCause();
if (rootCause instanceof BeanCurrentlyInCreationException) {
BeanCreationException bce = (BeanCreationException) rootCause;
String bceBeanName = bce.getBeanName();
if (bceBeanName != null && this.beanFactory.isCurrentlyInCreation(bceBeanName)) {
if (logger.isTraceEnabled()) {
logger.trace("Skipping advisor '" + name +
"' with dependency on currently created bean: " + ex.getMessage());
}
// Ignore: indicates a reference back to the bean we're trying to advise.
// We want to find advisors other than the currently created bean itself.
continue;
}
}
throw ex;
}
}
}
}
return advisors;
}
AnnotationAwareAspectJAutoProxyCreator使用父类findCandidateAdvisors()方法获取容器内所有的通知器后，再使用BeanFactoryAspectJAdvisorsBuilder来发掘@Aspect代表的通知器。这个BeanFactoryAspectJAdvisorsBuilder也是在通过调用setFactory()方法的时候实例化的，是AnnotationAwareAspectJAutoProxyCreator的内部类，通过继承BeanFactoryAspectJAdvisorsBuilder拥有了buildAspectJAdvisors()的能力，并重写了isEligibleBean()方法，方法的具体实现是直接调用AnnotationAwareAspectJAutoProxyCreator的isEligibleAspectBean()方法。
@Override
protected void initBeanFactory(ConfigurableListableBeanFactory beanFactory) {
super.initBeanFactory(beanFactory);
if (this.aspectJAdvisorFactory == null) {
this.aspectJAdvisorFactory = new ReflectiveAspectJAdvisorFactory(beanFactory);
}
this.aspectJAdvisorsBuilder =
new BeanFactoryAspectJAdvisorsBuilderAdapter(beanFactory, this.aspectJAdvisorFactory);
}
protected boolean isEligibleAspectBean(String beanName) {
//默认是null
if (this.includePatterns == null) {
return true;
}
else {
//正则过滤
for (Pattern pattern : this.includePatterns) {
if (pattern.matcher(beanName).matches()) {
return true;
}
}
return false;
}
}
//寻找被@Aspect注解的类，返回一个Spring AOP的通知器代表它，
//为这个类的每个通知方法创建一个通知器
public List<Advisor> buildAspectJAdvisors() {
List<String> aspectNames = this.aspectBeanNames;
if (aspectNames == null) {
synchronized (this) {
aspectNames = this.aspectBeanNames;
if (aspectNames == null) {
List<Advisor> advisors = new ArrayList<>();
aspectNames = new ArrayList<>();
String[] beanNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
this.beanFactory, Object.class, true, false);
for (String beanName : beanNames) {
//使用正则做一层过滤
if (!isEligibleBean(beanName)) {
continue;
}
// We must be careful not to instantiate beans eagerly as in this case they
// would be cached by the Spring container but would not have been weaved.
Class<?> beanType = this.beanFactory.getType(beanName);
if (beanType == null) {
continue;
}
//判断该bean是否是@Aspect类
if (this.advisorFactory.isAspect(beanType)) {
aspectNames.add(beanName);
AspectMetadata amd = new AspectMetadata(beanType, beanName);
//@Aspect value默认情况
if (amd.getAjType().getPerClause().getKind() == PerClauseKind.SINGLETON) {
MetadataAwareAspectInstanceFactory factory =
new BeanFactoryAspectInstanceFactory(this.beanFactory, beanName);
//
List<Advisor> classAdvisors = this.advisorFactory.getAdvisors(factory);
if (this.beanFactory.isSingleton(beanName)) {
this.advisorsCache.put(beanName, classAdvisors);
}
else {
this.aspectFactoryCache.put(beanName, factory);
}
advisors.addAll(classAdvisors);
}
else {
// Per target or per this.
if (this.beanFactory.isSingleton(beanName)) {
throw new IllegalArgumentException("Bean with name '" + beanName +
"' is a singleton, but aspect instantiation model is not singleton");
}
MetadataAwareAspectInstanceFactory factory =
new PrototypeAspectInstanceFactory(this.beanFactory, beanName);
this.aspectFactoryCache.put(beanName, factory);
advisors.addAll(this.advisorFactory.getAdvisors(factory));
}
}
}
this.aspectBeanNames = aspectNames;
return advisors;
}
}
}
if (aspectNames.isEmpty()) {
return Collections.emptyList();
}
List<Advisor> advisors = new ArrayList<>();
for (String aspectName : aspectNames) {
List<Advisor> cachedAdvisors = this.advisorsCache.get(aspectName);
if (cachedAdvisors != null) {
advisors.addAll(cachedAdvisors);
}
else {
MetadataAwareAspectInstanceFactory factory = this.aspectFactoryCache.get(aspectName);
advisors.addAll(this.advisorFactory.getAdvisors(factory));
}
}
return advisors;
}
上面的核心方法就是这三行：
MetadataAwareAspectInstanceFactory factory =
new BeanFactoryAspectInstanceFactory(this.beanFactory, beanName);
List<Advisor> classAdvisors = this.advisorFactory.getAdvisors(factory);
BeanFactoryAspectInstanceFactory包含当前的bean name，通过ReflectiveAspectJAdvisorFactory的getAdvisors()方法返回此bean name的@Aspect类代表的所有的Advisor。BeanFactoryAspectInstanceFactory这个类主要用于获取@Aspect类的AspectMetadata对象。
public class AspectMetadata implements Serializable {
//bean name
private final String aspectName;
//bean class
private final Class<?> aspectClass;
//AspectJ反射信息，参考AjTypeImpl
private transient AjType<?> ajType;
//默认情况@Aspect value=singleton --> Pointcut.TRUE
private final Pointcut perClausePointcut;
}
下面是ReflectiveAspectJAdvisorFactory的getAdvisors()方法。
@Override
public List<Advisor> getAdvisors(MetadataAwareAspectInstanceFactory aspectInstanceFactory) {
Class<?> aspectClass = aspectInstanceFactory.getAspectMetadata().getAspectClass();
String aspectName = aspectInstanceFactory.getAspectMetadata().getAspectName();
//非抽象父类不能是@Aspect类
validate(aspectClass);
// We need to wrap the MetadataAwareAspectInstanceFactory with a decorator
// so that it will only instantiate once.
MetadataAwareAspectInstanceFactory lazySingletonAspectInstanceFactory =
new LazySingletonAspectInstanceFactoryDecorator(aspectInstanceFactory);
List<Advisor> advisors = new ArrayList<>();
//循环处理没有@Pointcut的方法
for (Method method : getAdvisorMethods(aspectClass)) {
Advisor advisor = getAdvisor(method, lazySingletonAspectInstanceFactory, advisors.size(), aspectName);
if (advisor != null) {
advisors.add(advisor);
}
}
// If it's a per target aspect, emit the dummy instantiating aspect.
if (!advisors.isEmpty() && lazySingletonAspectInstanceFactory.getAspectMetadata().isLazilyInstantiated()) {
Advisor instantiationAdvisor = new SyntheticInstantiationAdvisor(lazySingletonAspectInstanceFactory);
advisors.add(0, instantiationAdvisor);
}
// Find introduction fields.
for (Field field : aspectClass.getDeclaredFields()) {
//为切入点引入共同的接口实现，参考
//https://blog.csdn.net/elim168/article/details/78166296
Advisor advisor = getDeclareParentsAdvisor(field);
if (advisor != null) {
advisors.add(advisor);
}
}
return advisors;
}
//一个非@Pointcut方法对应一个通知器
public Advisor getAdvisor(Method candidateAdviceMethod, MetadataAwareAspectInstanceFactory aspectInstanceFactory,
int declarationOrderInAspect, String aspectName) {
validate(aspectInstanceFactory.getAspectMetadata().getAspectClass());
//@Pointcut, @Around,@Before, @After, @AfterReturning,@AfterThrowing都会对应一个AspectJExpressionPointcut
AspectJExpressionPointcut expressionPointcut = getPointcut(
candidateAdviceMethod, aspectInstanceFactory.getAspectMetadata().getAspectClass());
if (expressionPointcut == null) {
return null;
}
//绑定切入点与通知，通知就是方法
return new InstantiationModelAwarePointcutAdvisorImpl(expressionPointcut, candidateAdviceMethod,
this, aspectInstanceFactory, declarationOrderInAspect, aspectName);
}
总结：基于注解的AOP实现，最终还是要将注解类转换成相应的Adviser、advice、Pointcut的。