spring5 源码深度解析—– 创建AOP代理之获取增强器

如果 bean 存在  Aspect.class 注解，就可以获取此bean中的增强器了，接着我们来看看  List classAdvisors = this.advisorFactory.getAdvisors(factory);

@Override
public List getAdvisors(MetadataAwareAspectInstanceFactory aspectInstanceFactory) {
    // 获取标记为AspectJ的类
    Class aspectClass = aspectInstanceFactory.getAspectMetadata().getAspectClass();
    // 获取标记为AspectJ的name
    String aspectName = aspectInstanceFactory.getAspectMetadata().getAspectName();
    validate(aspectClass);

    // We need to wrap the MetadataAwareAspectInstanceFactory with a decorator
    // so that it will only instantiate once.
    MetadataAwareAspectInstanceFactory lazySingletonAspectInstanceFactory =
            new LazySingletonAspectInstanceFactoryDecorator(aspectInstanceFactory);

    List advisors = new ArrayList();
    
    // 对aspectClass的每一个带有注解的方法进行循环（带有PointCut注解的方法除外），取得Advisor，并添加到集合里。
    // (这是里应该是取得Advice，然后取得我们自己定义的切面类中PointCut，组合成Advisor)
    for (Method method : getAdvisorMethods(aspectClass)) {
        //将类中的方法封装成Advisor
        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()) {
        Advisor advisor = getDeclareParentsAdvisor(field);
        if (advisor != null) {
            advisors.add(advisor);
        }
    }

    return advisors;
}

普通增强器的获取

普通增强器的获取逻辑通过 getAdvisor 方法实现，实现步骤包括对切点的注解的获取以及根据注解信息生成增强。我们先来看看  getAdvisorMethods(aspectClass)，这个方法，通过很巧妙的使用接口，定义一个匿名回调，把带有注解的Method都取得出来，放到集合里

private List getAdvisorMethods(Class aspectClass) {
    final List methods = new LinkedList();
    ReflectionUtils.doWithMethods(aspectClass, new ReflectionUtils.MethodCallback() {
        @Override
        public void doWith(Method method) throws IllegalArgumentException {
            // Exclude pointcuts
            // 将没有使用Pointcut.class注解的方法加入到集合中
            if (AnnotationUtils.getAnnotation(method, Pointcut.class) == null) {
                methods.add(method);
            }
        }
    });
    Collections.sort(methods, METHOD_COMPARATOR);
    return methods;
}

public static void doWithMethods(Class clazz, MethodCallback mc, @Nullable MethodFilter mf) {
    // Keep backing up the inheritance hierarchy.
    // 通过反射获取类中所有的方法
    Method[] methods = getDeclaredMethods(clazz);
    //遍历所有的方法
    for (Method method : methods) {
        if (mf != null && !mf.matches(method)) {
            continue;
        }
        try {
            //调用函数体
            mc.doWith(method);
        }
        catch (IllegalAccessException ex) {
            throw new IllegalStateException("Not allowed to access method '" + method.getName() + "': " + ex);
        }
    }
    if (clazz.getSuperclass() != null) {
        doWithMethods(clazz.getSuperclass(), mc, mf);
    }
    else if (clazz.isInterface()) {
        for (Class superIfc : clazz.getInterfaces()) {
            doWithMethods(superIfc, mc, mf);
        }
    }
}

普通增强器的获取逻辑通过 getAdvisor 方法来实现，实现步骤包括对切点的注解以及根据注解信息生成增强。

public Advisor getAdvisor(Method candidateAdviceMethod, MetadataAwareAspectInstanceFactory aif,
        int declarationOrderInAspect, String aspectName) {

    validate(aif.getAspectMetadata().getAspectClass());
    // 获取PointCut信息（主要是PointCut里的表达式）
    // 把Method对象也传进去的目的是，比较Method对象上的注解，是不是下面注解其中一个
    // 如果不是，返回null；如果是，就把取得PointCut内容包装返回
    // 被比较注解：Before.class, Around.class, After.class, AfterReturning.class, AfterThrowing.class, Pointcut.class
    AspectJExpressionPointcut ajexp =
            getPointcut(candidateAdviceMethod, aif.getAspectMetadata().getAspectClass());
    if (ajexp == null) {
        return null;
    }
    // 根据PointCut信息生成增强器
    return new InstantiationModelAwarePointcutAdvisorImpl(
            this, ajexp, aif, candidateAdviceMethod, declarationOrderInAspect, aspectName);
}

（1）切点信息的获取 

所谓获取切点信息就是指定注解的表达式信息的获取，如@Before(“test()”)。

private AspectJExpressionPointcut getPointcut(Method candidateAdviceMethod, Class candidateAspectClass) {
    // 获取方法上的注解
    // 比较Method对象上的注解，是不是下面注解其中一个，如果不是返回null
    // 被比较注解：Before.class, Around.class, After.class, AfterReturning.class, AfterThrowing.class, Pointcut.class
    AspectJAnnotation aspectJAnnotation = AbstractAspectJAdvisorFactory.findAspectJAnnotationOnMethod(candidateAdviceMethod);
    if (aspectJAnnotation == null) {
        return null;
    }
    // 使用AspectJExpressionPointcut 实例封装获取的信息
    AspectJExpressionPointcut ajexp = new AspectJExpressionPointcut(candidateAspectClass, new String[0], new Class[0]);

    // 提取得到的注解中的表达式如：
    // @Pointcut（"execution（* test.TestBean.*(..)）"）
    ajexp.setExpression(aspectJAnnotation.getPointcutExpression());
    return ajexp;
}

详细看下上面方法中使用到的方法findAspectJAnnotationOnMethod

protected static AspectJAnnotation findAspectJAnnotationOnMethod(Method method) {
    // 设置要查找的注解类，看看方法的上注解是不是这些注解其中之一
    Class[] classesToLookFor = new Class[] {
            Before.class, Around.class, After.class, AfterReturning.class, AfterThrowing.class, Pointcut.class};
    for (Class c : classesToLookFor) {
        AspectJAnnotation foundAnnotation = findAnnotation(method, (Class) c);
        if (foundAnnotation != null) {
            return foundAnnotation;
        }
    }
    return null;
}

在上面方法中又用到了方法findAnnotation，继续跟踪代码：

此方法的功能是获取指定方法上的注解并使用AspectJAnnotation封装。

（2）根据切点信息生成增强类 

所有的增强都有Advisor实现类InstantiationModelAwarePontcutAdvisorImpl进行统一封装的。我们看下其构造函数：

public InstantiationModelAwarePointcutAdvisorImpl(AspectJAdvisorFactory af, AspectJExpressionPointcut ajexp,
        MetadataAwareAspectInstanceFactory aif, Method method, int declarationOrderInAspect, String aspectName) {

    this.declaredPointcut = ajexp;
    this.method = method;
    this.atAspectJAdvisorFactory = af;
    this.aspectInstanceFactory = aif;
    this.declarationOrder = declarationOrderInAspect;
    this.aspectName = aspectName;

    if (aif.getAspectMetadata().isLazilyInstantiated()) {
        // Static part of the pointcut is a lazy type.
        Pointcut preInstantiationPointcut =
                Pointcuts.union(aif.getAspectMetadata().getPerClausePointcut(), this.declaredPointcut);

        // Make it dynamic: must mutate from pre-instantiation to post-instantiation state.
        // If it's not a dynamic pointcut, it may be optimized out
        // by the Spring AOP infrastructure after the first evaluation.
        this.pointcut = new PerTargetInstantiationModelPointcut(this.declaredPointcut, preInstantiationPointcut, aif);
        this.lazy = true;
    }
    else {
        // A singleton aspect.
        // 初始化Advice
        this.instantiatedAdvice = instantiateAdvice(this.declaredPointcut);
        this.pointcut = declaredPointcut;
        this.lazy = false;
    }
}

通过对上面构造函数的分析，发现封装过程只是简单地将信息封装在类的实例中，所有的额信息单纯地复制。在实例初始化的过程中还完成了对于增强器的初始化。因为不同的增强所体现的逻辑是不同的，比如@Before（“test（）”）与After（“test（）”）标签的不同就是增强器增强的位置不同，所以就需要不同的增强器来完成不同的逻辑，而根据注解中的信息初始化对应的额增强器就是在instantiateAdvice函数中实现的，继续跟踪代码：

private Advice instantiateAdvice(AspectJExpressionPointcut pointcut) {
    Advice advice = this.aspectJAdvisorFactory.getAdvice(this.aspectJAdviceMethod, pointcut,
            this.aspectInstanceFactory, this.declarationOrder, this.aspectName);
    return (advice != null ? advice : EMPTY_ADVICE);
}

    @Override
@Nullable
public Advice getAdvice(Method candidateAdviceMethod, AspectJExpressionPointcut expressionPointcut,
        MetadataAwareAspectInstanceFactory aspectInstanceFactory, int declarationOrder, String aspectName) {

    Class candidateAspectClass = aspectInstanceFactory.getAspectMetadata().getAspectClass();
    validate(candidateAspectClass);

    AspectJAnnotation aspectJAnnotation =
            AbstractAspectJAdvisorFactory.findAspectJAnnotationOnMethod(candidateAdviceMethod);
    if (aspectJAnnotation == null) {
        return null;
    }

    // If we get here, we know we have an AspectJ method.
    // Check that it's an AspectJ-annotated class
    if (!isAspect(candidateAspectClass)) {
        throw new AopConfigException("Advice must be declared inside an aspect type: " +
                "Offending method '" + candidateAdviceMethod + "' in class [" +
                candidateAspectClass.getName() + "]");
    }

    if (logger.isDebugEnabled()) {
        logger.debug("Found AspectJ method: " + candidateAdviceMethod);
    }

    AbstractAspectJAdvice springAdvice;
    // 根据不同的注解类型封装不同的增强器
    switch (aspectJAnnotation.getAnnotationType()) {
        case AtBefore:
            springAdvice = new AspectJMethodBeforeAdvice(
                    candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
            break;
        case AtAfter:
            springAdvice = new AspectJAfterAdvice(
                    candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
            break;
        case AtAfterReturning:
            springAdvice = new AspectJAfterReturningAdvice(
                    candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
            AfterReturning afterReturningAnnotation = (AfterReturning) aspectJAnnotation.getAnnotation();
            if (StringUtils.hasText(afterReturningAnnotation.returning())) {
                springAdvice.setReturningName(afterReturningAnnotation.returning());
            }
            break;
        case AtAfterThrowing:
            springAdvice = new AspectJAfterThrowingAdvice(
                    candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
            AfterThrowing afterThrowingAnnotation = (AfterThrowing) aspectJAnnotation.getAnnotation();
            if (StringUtils.hasText(afterThrowingAnnotation.throwing())) {
                springAdvice.setThrowingName(afterThrowingAnnotation.throwing());
            }
            break;
        case AtAround:
            springAdvice = new AspectJAroundAdvice(
                    candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
            break;
        case AtPointcut:
            if (logger.isDebugEnabled()) {
                logger.debug("Processing pointcut '" + candidateAdviceMethod.getName() + "'");
            }
            return null;
        default:
            throw new UnsupportedOperationException(
                    "Unsupported advice type on method: " + candidateAdviceMethod);
    }

    // Now to configure the advice...
    springAdvice.setAspectName(aspectName);
    springAdvice.setDeclarationOrder(declarationOrder);
    String[] argNames = this.parameterNameDiscoverer.getParameterNames(candidateAdviceMethod);
    if (argNames != null) {
        springAdvice.setArgumentNamesFromStringArray(argNames);
    }
    springAdvice.calculateArgumentBindings();

    return springAdvice;
}

从上述函数代码中可以看到，Spring会根据不同的注解生成不同的增强器，正如代码switch (aspectJAnnotation.getAnnotationType())，根据不同的类型来生成。例如AtBefore会对应AspectJMethodBeforeAdvice。在AspectJMethodBeforeAdvice中完成了增强逻辑，这里的 AspectJMethodBeforeAdvice 最后会被适配器封装成 MethodBeforeAdviceInterceptor， 下一篇文章中我们具体分析，具体看下其代码：

MethodBeforeAdviceInterceptor

public class MethodBeforeAdviceInterceptor implements MethodInterceptor, Serializable {

    private MethodBeforeAdvice advice;

    public MethodBeforeAdviceInterceptor(MethodBeforeAdvice advice) {
        Assert.notNull(advice, "Advice must not be null");
        this.advice = advice;
    }

    @Override
    public Object invoke(MethodInvocation mi) throws Throwable {
        this.advice.before(mi.getMethod(), mi.getArguments(), mi.getThis());
        return mi.proceed();
    }

}

其中的MethodBeforeAdvice代表着前置增强的AspectJMethodBeforeAdvice，跟踪before方法：

AspectJMethodBeforeAdvice.java

public class AspectJMethodBeforeAdvice extends AbstractAspectJAdvice implements MethodBeforeAdvice, Serializable {

    public AspectJMethodBeforeAdvice(
            Method aspectJBeforeAdviceMethod, AspectJExpressionPointcut pointcut, AspectInstanceFactory aif) {

        super(aspectJBeforeAdviceMethod, pointcut, aif);
    }


    @Override
    public void before(Method method, Object[] args, @Nullable Object target) throws Throwable {
        //直接调用增强方法
        invokeAdviceMethod(getJoinPointMatch(), null, null);
    }

}

protected Object invokeAdviceMethod(
        @Nullable JoinPointMatch jpMatch, @Nullable Object returnValue, @Nullable Throwable ex)
        throws Throwable {

    return invokeAdviceMethodWithGivenArgs(argBinding(getJoinPoint(), jpMatch, returnValue, ex));
}

protected Object invokeAdviceMethodWithGivenArgs(Object[] args) throws Throwable {
    Object[] actualArgs = args;
    if (this.aspectJAdviceMethod.getParameterCount() == 0) {
        actualArgs = null;
    }
    try {
        ReflectionUtils.makeAccessible(this.aspectJAdviceMethod);
        // TODO AopUtils.invokeJoinpointUsingReflection
        // 通过反射调用AspectJ注解类中的增强方法
        return this.aspectJAdviceMethod.invoke(this.aspectInstanceFactory.getAspectInstance(), actualArgs);
    }
    catch (IllegalArgumentException ex) {
        throw new AopInvocationException("Mismatch on arguments to advice method [" +
                this.aspectJAdviceMethod + "]; pointcut expression [" +
                this.pointcut.getPointcutExpression() + "]", ex);
    }
    catch (InvocationTargetException ex) {
        throw ex.getTargetException();
    }
}

invokeAdviceMethodWithGivenArgs方法中的aspectJAdviceMethod正是对与前置增强的方法，在这里实现了调用。

后置增强与前置增强有稍许不一致的地方。回顾之前讲过的前置增强，大致的结构是在拦截器链中放置MethodBeforeAdviceInterceptor，而在MethodBeforeAdviceInterceptor中又放置了AspectJMethodBeforeAdvice，并在调用invoke时首先串联调用。但是在后置增强的时候却不一样，没有提供中间的类，而是直接在拦截器中使用了中间的AspectJAfterAdvice，也就是直接实现了 MethodInterceptor 。

public class AspectJAfterAdvice extends AbstractAspectJAdvice
        implements MethodInterceptor, AfterAdvice, Serializable {

    public AspectJAfterAdvice(
            Method aspectJBeforeAdviceMethod, AspectJExpressionPointcut pointcut, AspectInstanceFactory aif) {

        super(aspectJBeforeAdviceMethod, pointcut, aif);
    }


    @Override
    public Object invoke(MethodInvocation mi) throws Throwable {
        try {
            return mi.proceed();
        }
        finally {
            // 激活增强方法
            invokeAdviceMethod(getJoinPointMatch(), null, null);
        }
    }

    @Override
    public boolean isBeforeAdvice() {
        return false;
    }

    @Override
    public boolean isAfterAdvice() {
        return true;
    }

}

其他的几个增强器，留在下一篇文章中具体来看

寻找匹配的增强器

前面的函数中已经完成了所有增强器的解析，但是对于所有增强器来讲，并不一定都适用于当前的bean，还要挑取出适合的增强器，也就是满足我们配置的通配符的增强器。具体实现在findAdvisorsThatCanApply中。

protected List findAdvisorsThatCanApply(
        List candidateAdvisors, Class beanClass, String beanName) {

    ProxyCreationContext.setCurrentProxiedBeanName(beanName);
    try {
        // 过滤已经得到的advisors
        return AopUtils.findAdvisorsThatCanApply(candidateAdvisors, beanClass);
    }
    finally {
        ProxyCreationContext.setCurrentProxiedBeanName(null);
    }
}

继续看findAdvisorsThatCanApply：

public static List findAdvisorsThatCanApply(List candidateAdvisors, Class clazz) {
    if (candidateAdvisors.isEmpty()) {
        return candidateAdvisors;
    }
    List eligibleAdvisors = new ArrayList();
    // 首先处理引介增强
    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;
        }
        // 对于普通bean的处理
        if (canApply(candidate, clazz, hasIntroductions)) {
            eligibleAdvisors.add(candidate);
        }
    }
    return eligibleAdvisors;
}

findAdvisorsThatCanApply函数的主要功能是寻找增强器中适用于当前class的增强器。引介增强与普通的增强的处理是不一样的，所以分开处理。而对于真正的匹配在canApply中实现。

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;
        return canApply(pca.getPointcut(), targetClass, hasIntroductions);
    }
    else {
        // It doesn't have a pointcut so we assume it applies.
        return true;
    }
}

public static boolean canApply(Pointcut pc, Class targetClass, boolean hasIntroductions) {
    Assert.notNull(pc, "Pointcut must not be null");
    //通过Pointcut的条件判断此类是否能匹配
    if (!pc.getClassFilter().matches(targetClass)) {
        return false;
    }

    MethodMatcher methodMatcher = pc.getMethodMatcher();
    if (methodMatcher == MethodMatcher.TRUE) {
        // No need to iterate the methods if we're matching any method anyway...
        return true;
    }

    IntroductionAwareMethodMatcher introductionAwareMethodMatcher = null;
    if (methodMatcher instanceof IntroductionAwareMethodMatcher) {
        introductionAwareMethodMatcher = (IntroductionAwareMethodMatcher) methodMatcher;
    }

    Set<Class> classes = new LinkedHashSet();
    if (!Proxy.isProxyClass(targetClass)) {
        classes.add(ClassUtils.getUserClass(targetClass));
    }
    classes.addAll(ClassUtils.getAllInterfacesForClassAsSet(targetClass));

    for (Class clazz : classes) {
        //反射获取类中所有的方法
        Method[] methods = ReflectionUtils.getAllDeclaredMethods(clazz);
        for (Method method : methods) {
            //根据匹配原则判断该方法是否能匹配Pointcut中的规则，如果有一个方法能匹配，则返回true
            if (introductionAwareMethodMatcher != null ?
                    introductionAwareMethodMatcher.matches(method, targetClass, hasIntroductions) :
                    methodMatcher.matches(method, targetClass)) {
                return true;
            }
        }
    }

    return false;
}

首先判断bean是否满足切点的规则，如果能满足，则获取bean的所有方法，判断是否有方法能匹配规则，有方法匹配规则，就代表此 Advisor 能作用于该bean,然后将该Advisor加入 eligibleAdvisors 集合中。

我们以注解的规则来看看bean中的method是怎样匹配 Pointcut中的规则

AnnotationMethodMatcher

@Override
public boolean matches(Method method, Class targetClass) {
    if (matchesMethod(method)) {
        return true;
    }
    // Proxy classes never have annotations on their redeclared methods.
    if (Proxy.isProxyClass(targetClass)) {
        return false;
    }
    // The method may be on an interface, so let's check on the target class as well.
    Method specificMethod = AopUtils.getMostSpecificMethod(method, targetClass);
    return (specificMethod != method && matchesMethod(specificMethod));
}

private boolean matchesMethod(Method method) {
    //可以看出判断该Advisor是否使用于bean中的method，只需看method上是否有Advisor的注解
    return (this.checkInherited ? AnnotatedElementUtils.hasAnnotation(method, this.annotationType) :
            method.isAnnotationPresent(this.annotationType));
}

至此，我们在后置处理器中找到了所有匹配Bean中的增强器，下一章讲解如何使用找到切面，来创建代理。