本文将通过阅读AnnotationAwareAspectJAutoProxyCreator后置处理器的源码，分析其解析AOP通知、匹配切入点和创建AOP代理的流程。

入口

AnnotationAwareAspectJAutoProxyCreator是一个BeanPostProcessor实现，他在容器进行initializeBean的时候被调用：

在这里插入图片描述

核心的BeanPostProcessor方法实现都在其父类AbstractAutoProxyCreator中实现。

wrapIfNecessary方法

在其父类AbstractAutoProxyCreator的postProcessAfterInitialization方法中。

核心功能：

查找AOP Advisor
创建AOP代理

protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
	// 最开始是一些是否需要AOP的判断，如果不需要或者已经创建代理，则直接返回了

	// Create proxy if we have advice.
    // 查找AOP Advisor
	Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(bean.getClass(), beanName, null);
	if (specificInterceptors != DO_NOT_PROXY) {
		this.advisedBeans.put(cacheKey, Boolean.TRUE);
        // 创建AOP代理
		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;
}

getAdvicesAndAdvisorsForBean方法

查找AOP Advisor

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();
}

// Find all eligible Advisors for auto-proxying this class.
protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
    // 此处分为两部分：
    // 1. 查找Spring容器里面注入的Advisor
    // 2. 解析所有的AspectJ AOP并创建Advisor
    // 实现逻辑在AnnotationAwareAspectJAutoProxyCreator类中
	List<Advisor> candidateAdvisors = findCandidateAdvisors();
    // Search the given candidate Advisors to find all Advisors that can apply to the specified bean.
	List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
    // Add an ExposeInvocationInterceptor to the beginning of the advice chain.
    // This additional advice is needed when using AspectJ pointcut expressions and 
    // when using AspectJ-style advice.
	extendAdvisors(eligibleAdvisors);
	if (!eligibleAdvisors.isEmpty()) {
		eligibleAdvisors = sortAdvisors(eligibleAdvisors);
	}
	return eligibleAdvisors;
}

// AnnotationAwareAspectJAutoProxyCreator.findCandidateAdvisors
protected List<Advisor> findCandidateAdvisors() {
	// Add all the Spring advisors found according to superclass rules.
    // 查找Spring容器里面注入的Advisor，代码就不再展开记录
	List<Advisor> advisors = super.findCandidateAdvisors();
	// Build Advisors for all AspectJ aspects in the bean factory.
    // 解析所有的AspectJ AOP并创建Advisor
	if (this.aspectJAdvisorsBuilder != null) {
		advisors.addAll(this.aspectJAdvisorsBuilder.buildAspectJAdvisors());
	}
	return advisors;
}

过滤当前Bean可用Advisor

findAdvisorsThatCanApply方法用于过滤可用Advisor：

protected List<Advisor> findAdvisorsThatCanApply(
		List<Advisor> candidateAdvisors, Class<?> beanClass, String beanName) {

	ProxyCreationContext.setCurrentProxiedBeanName(beanName);
	try {
		return AopUtils.findAdvisorsThatCanApply(candidateAdvisors, beanClass);
	} finally {
		ProxyCreationContext.setCurrentProxiedBeanName(null);
	}
}

AopUtils.findAdvisorsThatCanApply方法：

// Determine the sublist of the candidateAdvisors list that is applicable to the given class.
public static List<Advisor> findAdvisorsThatCanApply(List<Advisor> candidateAdvisors, Class<?> clazz) {
	List<Advisor> eligibleAdvisors = new ArrayList<>();
	for (Advisor candidate : candidateAdvisors) {
		if (candidate instanceof IntroductionAdvisor && canApply(candidate, clazz)) {
			eligibleAdvisors.add(candidate);
		}
	}
	boolean hasIntroductions = !eligibleAdvisors.isEmpty();
	for (Advisor candidate : candidateAdvisors) {
		if (candidate instanceof IntroductionAdvisor) {
			// already processed
			continue;
		}
		if (canApply(candidate, clazz, hasIntroductions)) {
			eligibleAdvisors.add(candidate);
		}
	}
	return eligibleAdvisors;
}

public static boolean canApply(Advisor advisor, Class<?> targetClass, boolean hasIntroductions) {
	if (advisor instanceof IntroductionAdvisor) {
		return ((IntroductionAdvisor) advisor).getClassFilter().matches(targetClass);
	} else if (advisor instanceof PointcutAdvisor) {
		PointcutAdvisor pca = (PointcutAdvisor) advisor;
        // 使用pointcut判断
		return canApply(pca.getPointcut(), targetClass, hasIntroductions);
	} else {
		return true;
	}
}

排序

在查找Advisor集的过程中，有一步是Advisor集排序：

protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
	List<Advisor> candidateAdvisors = findCandidateAdvisors();
	List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
	extendAdvisors(eligibleAdvisors);
	if (!eligibleAdvisors.isEmpty()) {
        // 排序
		eligibleAdvisors = sortAdvisors(eligibleAdvisors);
	}
	return eligibleAdvisors;
}

protected List<Advisor> sortAdvisors(List<Advisor> advisors) {
	List<PartiallyComparableAdvisorHolder> partiallyComparableAdvisors = new ArrayList<>(advisors.size());
	for (Advisor advisor : advisors) {
		partiallyComparableAdvisors.add(
				new PartiallyComparableAdvisorHolder(advisor, DEFAULT_PRECEDENCE_COMPARATOR));
	}
	List<PartiallyComparableAdvisorHolder> sorted = PartialOrder.sort(partiallyComparableAdvisors);
	if (sorted != null) {
		List<Advisor> result = new ArrayList<>(advisors.size());
		for (PartiallyComparableAdvisorHolder pcAdvisor : sorted) {
			result.add(pcAdvisor.getAdvisor());
		}
		return result;
	} else {
		return super.sortAdvisors(advisors);
	}
}

核心的排序逻辑都在DEFAULT_PRECEDENCE_COMPARATOR中，他是一个Comparator实现：

public int compare(Advisor o1, Advisor o2) {
	int advisorPrecedence = this.advisorComparator.compare(o1, o2);
    // 如果advisorComparator比较结果相同，将使用AspectJ相关的方法排序，此部分不分析
	if (advisorPrecedence == SAME_PRECEDENCE && declaredInSameAspect(o1, o2)) {
		advisorPrecedence = comparePrecedenceWithinAspect(o1, o2);
	}
	return advisorPrecedence;
}

advisorComparator也是一个Comparator实现，他内部有一些从Ordered实现方法、Order注解获取顺序的逻辑，此处不展开分析，了解即可。

创建AOP代理

// 创建AOP代理
Object proxy = createProxy(
		bean.getClass(), beanName, specificInterceptors, new SingletonTargetSource(bean));

createProxy入口方法

protected Object createProxy(Class<?> beanClass, String beanName,
		Object[] specificInterceptors, TargetSource targetSource) {

    // Expose the given target class for the specified bean, if possible.
	if (this.beanFactory instanceof ConfigurableListableBeanFactory) {
		AutoProxyUtils
            .exposeTargetClass((ConfigurableListableBeanFactory) this.beanFactory, beanName, beanClass);
	}

	ProxyFactory proxyFactory = new ProxyFactory();
	proxyFactory.copyFrom(this);

	if (!proxyFactory.isProxyTargetClass()) {
		if (shouldProxyTargetClass(beanClass, beanName)) {
			proxyFactory.setProxyTargetClass(true);
		}
		else {
			evaluateProxyInterfaces(beanClass, proxyFactory);
		}
	}

    // 构建AOP通知
	Advisor[] advisors = buildAdvisors(beanName, specificInterceptors);
	proxyFactory.addAdvisors(advisors);
	proxyFactory.setTargetSource(targetSource);
	customizeProxyFactory(proxyFactory);

	proxyFactory.setFrozen(this.freezeProxy);
	if (advisorsPreFiltered()) {
		proxyFactory.setPreFiltered(true);
	}

    // 创建代理
	return proxyFactory.getProxy(getProxyClassLoader());
}

// 构建AOP通知
protected Advisor[] buildAdvisors(String beanName, Object[] specificInterceptors) {
	Advisor[] commonInterceptors = resolveInterceptorNames();

	List<Object> allInterceptors = new ArrayList<>();
	if (specificInterceptors != null) {
		allInterceptors.addAll(Arrays.asList(specificInterceptors));
		if (commonInterceptors.length > 0) {
			// 不重要
		}
	}

	Advisor[] advisors = new Advisor[allInterceptors.size()];
	for (int i = 0; i < allInterceptors.size(); i++) {
		advisors[i] = this.advisorAdapterRegistry.wrap(allInterceptors.get(i));
	}
	return advisors;
}

proxyFactory.getProxy方法里面判断使用Cglib还是JdkProxy创建代理：

public Object getProxy(@Nullable ClassLoader classLoader) {
	return createAopProxy().getProxy(classLoader);
}

public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
	if (config.isOptimize() || config.isProxyTargetClass() || hasNoUserSuppliedProxyInterfaces(config)) {
		Class<?> targetClass = config.getTargetClass();
		if (targetClass == null) {
			// throw exception
		}
		if (targetClass.isInterface() || Proxy.isProxyClass(targetClass)) {
			return new JdkDynamicAopProxy(config);
		}
		return new ObjenesisCglibAopProxy(config);
	} else {
		return new JdkDynamicAopProxy(config);
	}
}

Cglib代理

从上面的代码可以看到，Cglib代理是使用ObjenesisCglibAopProxy实现类创建的。

继承关系是这样的：

AopProxy
  |-- CglibAopProxy
    |-- ObjenesisCglibAopProxy

Spring Cglib示例

下面代码演示如何是Spring Cglib创建一个代理类对象：

public static void main(String[] args) throws InstantiationException, IllegalAccessException {

  ClassLoader classLoader = CglibTest.class.getClassLoader();

  Enhancer enhancer = createEnhancer();

  // 设置目标类型
  enhancer.setSuperclass(LogService.class);

  enhancer.setClassLoader(classLoader);
  enhancer.setUseCache(false);
  enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);
  enhancer.setStrategy(new ClassLoaderAwareGeneratorStrategy(classLoader));

  // callback集
  Callback[] callbacks = new Callback[]{
      new MyMethodInterceptor()
  };
  Class<?>[] types = new Class<?>[callbacks.length];
  for (int x = 0; x < types.length; x++) {
    types[x] = callbacks[x].getClass();
  }
  enhancer.setCallbackTypes(types);

  // 创建代理类并实例化
  Class<?> proxyClass = enhancer.createClass();
  Object proxyInstance = proxyClass.newInstance();

  ((Factory) proxyInstance).setCallbacks(callbacks);

  LogService o = (LogService) proxyInstance;
  o.testServiceLog();
}

protected static Enhancer createEnhancer() {
  return new Enhancer();
}

private static class MyMethodInterceptor implements MethodInterceptor {

  @Override
  public Object intercept(
      Object enhancedConfigInstance, Method beanMethod,
      Object[] beanMethodArgs, MethodProxy cglibMethodProxy) throws Throwable {

    System.out.printf("MyMethodInterceptor %s args: %s\n",
        beanMethod.getName(), Arrays.toString(beanMethodArgs));

    return cglibMethodProxy.invokeSuper(enhancedConfigInstance, beanMethodArgs);
  }
}

CglibAopProxy.getProxy实现

public Object getProxy(ClassLoader classLoader) {

	try {
		Class<?> rootClass = this.advised.getTargetClass();

		Class<?> proxySuperClass = rootClass;
		if (rootClass.getName().contains(ClassUtils.CGLIB_CLASS_SEPARATOR)) {
			proxySuperClass = rootClass.getSuperclass();
			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...
		Enhancer enhancer = createEnhancer();
		if (classLoader != null) {
			enhancer.setClassLoader(classLoader);
			if (classLoader instanceof SmartClassLoader &&
					((SmartClassLoader) classLoader).isClassReloadable(proxySuperClass)) {
				enhancer.setUseCache(false);
			}
		}
		enhancer.setSuperclass(proxySuperClass);
		enhancer.setInterfaces(AopProxyUtils.completeProxiedInterfaces(this.advised));
		enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);
		enhancer.setStrategy(new ClassLoaderAwareGeneratorStrategy(classLoader));

        // 通过advisor创建cglib代理callback
		Callback[] 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 above
		enhancer.setCallbackFilter(
            new ProxyCallbackFilter(
				this.advised.getConfigurationOnlyCopy(),
                this.fixedInterceptorMap,
                this.fixedInterceptorOffset));
		enhancer.setCallbackTypes(types);

		// Generate the proxy class and create a proxy instance.
        // 生成代理对象并返回
		return createProxyClassAndInstance(enhancer, callbacks);
	} catch (CodeGenerationException | IllegalArgumentException ex) {
		// throw new AopConfigException
	} catch (Throwable ex) {
		// throw new AopConfigException
	}
}

getCallbacks

创建cglib callback对象，最核心的就是使用spring aop advisor创建了一个DynamicAdvisedInterceptor对象，让其作为代理对象的处理逻辑。

DynamicAdvisedInterceptor这个类会在后续解析AOP执行流程时再做介绍。

下图就是该方法封装DynamicAdvisedInterceptor对象的结构：

target - 封装原始的Bean对象
advisors - spring aop advisor集

在这里插入图片描述

createProxyClassAndInstance

这个方法在ObjenesisCglibAopProxy类实现：

protected Object createProxyClassAndInstance(Enhancer enhancer, Callback[] callbacks) {
    // Generate a new class if necessary and return it without creating a new instance.
    // This ignores any callbacks that have been set.
    // To create a new instance you will have to use reflection,
    // and methods called during the constructor will not be intercepted.
    // To avoid this problem, use the multi-arg create method.
    // 生成代理类
	Class<?> proxyClass = enhancer.createClass();
	Object proxyInstance = null;

	// 创建proxyInstance代理对象，实际上就是使用反射创建一个proxyClass的实例，代码省略

    // 设置callback代理拦截
	((Factory) proxyInstance).setCallbacks(callbacks);
	return proxyInstance;
}

Cglib生成代理类(暂时不分析)

不太懂，暂时不分析。

JDK代理

JDK代理示例

public static void main(String[] args) {

  LogService logService = new LogServiceImpl();

  Object proxyInstance = Proxy.newProxyInstance(
      SpringJdkProxyDemo.class.getClassLoader(),
      new Class[]{LogService.class},
      new MyInvocationHandler(logService));

  LogService o = (LogService) proxyInstance;
  o.log();
}

static class MyInvocationHandler implements InvocationHandler {

  private final Object object;

  public MyInvocationHandler(Object object) {
    this.object = object;
  }

  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    System.out.printf("MyInvocationHandler %s args: %s\n",
        method.getName(), Arrays.toString(args));
    return method.invoke(this.object, args);
  }
}

interface LogService {
  void log();
}

static class LogServiceImpl implements LogService {

  @Override
  public void log() {
    System.out.println("LogServiceImpl.log()");
  }
}

JdkDynamicAopProxy.getProxy

public Object getProxy(ClassLoader classLoader) {
	Class<?>[] proxiedInterfaces = AopProxyUtils.completeProxiedInterfaces(this.advised, true);
	findDefinedEqualsAndHashCodeMethods(proxiedInterfaces);
	return Proxy.newProxyInstance(classLoader, proxiedInterfaces, this);
}