基于注解的SpringAOP源码解析（二）

public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
    Object cacheKey = getCacheKey(beanClass, beanName);

    if (!StringUtils.hasLength(beanName) || !this.targetSourcedBeans.contains(beanName)) {
      if (this.advisedBeans.containsKey(cacheKey)) {
        return null;
      }
            //加载所有增强
      if (isInfrastructureClass(beanClass) || shouldSkip(beanClass, beanName)) {
        this.advisedBeans.put(cacheKey, Boolean.FALSE);
        return null;
      }
    }

    TargetSource targetSource = getCustomTargetSource(beanClass, beanName);
    if (targetSource != null) {
      if (StringUtils.hasLength(beanName)) {
        this.targetSourcedBeans.add(beanName);
      }
      Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(beanClass, beanName, targetSource);
      Object proxy = createProxy(beanClass, beanName, specificInterceptors, targetSource);
      this.proxyTypes.put(cacheKey, proxy.getClass());
      return proxy;
    }

    return null;
  }

protected boolean shouldSkip(Class<?> beanClass, String beanName) {
  
    //查找所有标识了@Aspect注解的类，这里是重点，接着往下看
    List<Advisor> candidateAdvisors = findCandidateAdvisors();
    for (Advisor advisor : candidateAdvisors) {
        if (advisor instanceof AspectJPointcutAdvisor) {
            if (((AbstractAspectJAdvice) advisor.getAdvice()).getAspectName().equals(beanName)) {
                return true;
            }
        }
    }
    return super.shouldSkip(beanClass, beanName);
    }


    protected List<Advisor> findCandidateAdvisors() {
        return this.advisorRetrievalHelper.findAdvisorBeans();
    }
    
    protected List<Advisor> findCandidateAdvisors() {
        List<Advisor> advisors = super.findCandidateAdvisors();
        //buildAspectJAdvisors是重点
           advisors.addAll(this.aspectJAdvisorsBuilder.buildAspectJAdvisors());
        return advisors;
    }

public List<Advisor> buildAspectJAdvisors() {
//所有Aspect类的名称集合
    List<String> aspectNames = this.aspectBeanNames;
    if (aspectNames == null) {
        synchronized (this) {
            aspectNames = this.aspectBeanNames;
            //这个双重检查是不是在学习安全的单例模式的时候见过
            if (aspectNames == null) {
                List<Advisor> advisors = new LinkedList<Advisor>();
                aspectNames = new LinkedList<String>();
                //获取所有Bean名称
                String[] beanNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
                        this.beanFactory, Object.class, true, false);
                for (String beanName : beanNames) {
                    //判断是否符合条件，比如说有时会排除一些类，不让这些类注入进Spring
                    if (!isEligibleBean(beanName)) {
                        continue;
                    }
           
                    Class<?> beanType = this.beanFactory.getType(beanName);
                    if (beanType == null) {
                        continue;
                    }
                    //判断Bean的Class上是否标识@Aspect注解
                    if (this.advisorFactory.isAspect(beanType)) {
                        aspectNames.add(beanName);
                        AspectMetadata amd = new AspectMetadata(beanType, beanName);
                        if (amd.getAjType().getPerClause().getKind() == PerClauseKind.SINGLETON) {
                            MetadataAwareAspectInstanceFactory factory =
                                    new BeanFactoryAspectInstanceFactory(this.beanFactory, beanName);
                            //下一步说，重点的重点
                            List<Advisor> classAdvisors = this.advisorFactory.getAdvisors(factory);
                            if (this.beanFactory.isSingleton(beanName)) {
                                //将解析的Bean名称及类上的增强缓存起来,每个Bean只解析一次
                                this.advisorsCache.put(beanName, classAdvisors);
                            }
                            else {
                                this.aspectFactoryCache.put(beanName, factory);
                            }
                            advisors.addAll(classAdvisors);
                        }
                        else {
                            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 LinkedList<Advisor>();
    for (String aspectName : aspectNames) {
        //从缓存中获取当前Bean的切面实例，如果不为空，则指明当前Bean的Class标识了@Aspect，且有切面方法
        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;
}

public List<Advisor> getAdvisors(MetadataAwareAspectInstanceFactory aspectInstanceFactory) {
    Class<?> aspectClass = aspectInstanceFactory.getAspectMetadata().getAspectClass();
    String aspectName = aspectInstanceFactory.getAspectMetadata().getAspectName();
    //校验类的合法性相关
    validate(aspectClass);

    MetadataAwareAspectInstanceFactory lazySingletonAspectInstanceFactory =
            new LazySingletonAspectInstanceFactoryDecorator(aspectInstanceFactory);

    List<Advisor> advisors = new LinkedList<Advisor>();
    //获取这个类所有的增强方法
    for (Method method : getAdvisorMethods(aspectClass)) {
        //生成增强实例
        Advisor advisor = getAdvisor(method, lazySingletonAspectInstanceFactory, advisors.size(), aspectName);
        if (advisor != null) {
            advisors.add(advisor);
        }
    }

    if (!advisors.isEmpty() && lazySingletonAspectInstanceFactory.getAspectMetadata().isLazilyInstantiated()) {
        Advisor instantiationAdvisor = new SyntheticInstantiationAdvisor(lazySingletonAspectInstanceFactory);
        advisors.add(0, instantiationAdvisor);
    }

    for (Field field : aspectClass.getDeclaredFields()) {
        Advisor advisor = getDeclareParentsAdvisor(field);
        if (advisor != null) {
            advisors.add(advisor);
        }
    }

    return advisors;
}

//获取类的的方法
private List<Method> getAdvisorMethods(Class<?> aspectClass) {
    final List<Method> methods = new LinkedList<Method>();
    ReflectionUtils.doWithMethods(aspectClass, new ReflectionUtils.MethodCallback() {
        @Override
        public void doWith(Method method) throws IllegalArgumentException {
                //在@Aspect标识的类内部排除@Pointcut标识之外的所有方法，得到的方法集合包括继承自父类的方法，包括继承自Object的方法
            if (AnnotationUtils.getAnnotation(method, Pointcut.class) == null) {
                methods.add(method);
            }
        }
    });
    //对得到的所有方法排序，
    //如果方法标识了切面注解，则按@Around, @Before, @After, @AfterReturning, @AfterThrowing的顺序排序
    //如果没有标识这些注解，则按方法名称的字符串排序,
    //有注解的方法排在无注解的方法之前
    //最后的排序应该是这样的Around.class, Before.class, After.class, AfterReturning.class, AfterThrowing.class。。。
    Collections.sort(methods, METHOD_COMPARATOR);
    return methods;
}

public Advisor getAdvisor(Method candidateAdviceMethod, MetadataAwareAspectInstanceFactory aspectInstanceFactory,
        int declarationOrderInAspect, String aspectName) {
    //再次校验类的合法性
    validate(aspectInstanceFactory.getAspectMetadata().getAspectClass());
    //切点表达式的包装类里面包含这些东西：execution(public * cn.shiyujun.service.IOCService.hollo(..))
    AspectJExpressionPointcut expressionPointcut = getPointcut(
            candidateAdviceMethod, aspectInstanceFactory.getAspectMetadata().getAspectClass());
    if (expressionPointcut == null) {
        return null;
    }
    //根据方法、切点、AOP实例工厂、类名、序号生成切面实例，详细代码往下看
    return new InstantiationModelAwarePointcutAdvisorImpl(expressionPointcut, candidateAdviceMethod,
            this, aspectInstanceFactory, declarationOrderInAspect, aspectName);
}

private AspectJExpressionPointcut getPointcut(Method candidateAdviceMethod, Class<?> candidateAspectClass) {
    //查询方法上的切面注解，根据注解生成相应类型的AspectJAnnotation,在调用AspectJAnnotation的构造函数的同时
    //根据注解value或pointcut属性得到切点表达式，有argNames则设置参数名称
    AspectJAnnotation<?> aspectJAnnotation =
            AbstractAspectJAdvisorFactory.findAspectJAnnotationOnMethod(candidateAdviceMethod);
    //过滤那些不含@Before, @Around, @After, @AfterReturning, @AfterThrowing注解的方法
    if (aspectJAnnotation == null) {
        return null;
    }
    //生成带表达式的切面切入点，设置其切入点表达式
    AspectJExpressionPointcut ajexp =
            new AspectJExpressionPointcut(candidateAspectClass, new String[0], new Class<?>[0]);
    ajexp.setExpression(aspectJAnnotation.getPointcutExpression());
    ajexp.setBeanFactory(this.beanFactory);
    return ajexp;
}

public InstantiationModelAwarePointcutAdvisorImpl(AspectJExpressionPointcut declaredPointcut,
      Method aspectJAdviceMethod, AspectJAdvisorFactory aspectJAdvisorFactory,
      MetadataAwareAspectInstanceFactory aspectInstanceFactory, int declarationOrder, String aspectName) {

    this.declaredPointcut = declaredPointcut;
    this.declaringClass = aspectJAdviceMethod.getDeclaringClass();
    this.methodName = aspectJAdviceMethod.getName();
    this.parameterTypes = aspectJAdviceMethod.getParameterTypes();
    this.aspectJAdviceMethod = aspectJAdviceMethod;
    this.aspectJAdvisorFactory = aspectJAdvisorFactory;
    this.aspectInstanceFactory = aspectInstanceFactory;
    this.declarationOrder = declarationOrder;
    this.aspectName = aspectName;

    if (aspectInstanceFactory.getAspectMetadata().isLazilyInstantiated()) {
      Pointcut preInstantiationPointcut = Pointcuts.union(
          aspectInstanceFactory.getAspectMetadata().getPerClausePointcut(), this.declaredPointcut);

      this.pointcut = new PerTargetInstantiationModelPointcut(
          this.declaredPointcut, preInstantiationPointcut, aspectInstanceFactory);
      this.lazy = true;
    }
    else {
      this.pointcut = this.declaredPointcut;
      this.lazy = false;
            //重点在这里
      this.instantiatedAdvice = instantiateAdvice(this.declaredPointcut);
    }
  }
    
    private Advice instantiateAdvice(AspectJExpressionPointcut pointcut) {
    //再往下看
    Advice advice = this.aspectJAdvisorFactory.getAdvice(this.aspectJAdviceMethod, pointcut,
        this.aspectInstanceFactory, this.declarationOrder, this.aspectName);
    return (advice != null ? advice : EMPTY_ADVICE);
  }

public class ReflectiveAspectJAdvisorFactory extends AbstractAspectJAdvisorFactory implements Serializable {

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

        Class<?> candidateAspectClass = aspectInstanceFactory.getAspectMetadata().getAspectClass();
        //又是一次校验
        validate(candidateAspectClass);

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

        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;
        //根据注解类型生成不同的通知实例
        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);
        }

        //设置通知方法所属的类
        springAdvice.setAspectName(aspectName);
        //设置通知的序号,同一个类中有多个切面注解标识的方法时,按上方说的排序规则来排序，
        //其序号就是此方法在列表中的序号，第一个就是0
        springAdvice.setDeclarationOrder(declarationOrder);
        //获取通知方法的所有参数
        String[] argNames = this.parameterNameDiscoverer.getParameterNames(candidateAdviceMethod);
        //将通知方法上的参数设置到通知中
        if (argNames != null) {
            springAdvice.setArgumentNamesFromStringArray(argNames);
        }
        //计算参数绑定工作，此方法详解请接着往下看
        springAdvice.calculateArgumentBindings();
        return springAdvice;
    }
}

public synchronized final void calculateArgumentBindings() {
    if (this.argumentsIntrospected || this.parameterTypes.length == 0) {
        return;
    }

    int numUnboundArgs = this.parameterTypes.length;
    Class<?>[] parameterTypes = this.aspectJAdviceMethod.getParameterTypes();
    //切面注解标识的方法第一个参数要求是JoinPoint,或StaticPart，若是@Around注解则也可以是ProceedingJoinPoint
    if (maybeBindJoinPoint(parameterTypes[0]) || maybeBindProceedingJoinPoint(parameterTypes[0])) {
        numUnboundArgs--;
    }
    else if (maybeBindJoinPointStaticPart(parameterTypes[0])) {
        numUnboundArgs--;
    }

    if (numUnboundArgs > 0) {
    //绑定属性
        bindArgumentsByName(numUnboundArgs);
    }

    this.argumentsIntrospected = true;
}
private void bindArgumentsByName(int numArgumentsExpectingToBind) {
    if (this.argumentNames == null) { //获取方法参数的名称
        this.argumentNames = createParameterNameDiscoverer().getParameterNames(this.aspectJAdviceMethod);
    }
    if (this.argumentNames != null) {
        // 往下看
        bindExplicitArguments(numArgumentsExpectingToBind);
    }
    else {
        throw new IllegalStateException("Advice method [" + this.aspectJAdviceMethod.getName() + "] " +
                "requires " + numArgumentsExpectingToBind + " arguments to be bound by name, but " +
                "the argument names were not specified and could not be discovered.");
    }
}

private void bindExplicitArguments(int numArgumentsLeftToBind) {
    //此属性用来存储方法未绑定的参数名称，及参数的序号
    this.argumentBindings = new HashMap<String, Integer>();

    int numExpectedArgumentNames = this.aspectJAdviceMethod.getParameterTypes().length;
    if (this.argumentNames.length != numExpectedArgumentNames) {
        throw new IllegalStateException("Expecting to find " + numExpectedArgumentNames +
                " arguments to bind by name in advice, but actually found " +
                this.argumentNames.length + " arguments.");
    }

    // So we match in number...,argumentIndexOffset代表第一个未绑定参数的顺序 
    int argumentIndexOffset = this.parameterTypes.length - numArgumentsLeftToBind;
    for (int i = argumentIndexOffset; i < this.argumentNames.length; i++) {
        //存储未绑定的参数名称及其顺序的映射关系
        this.argumentBindings.put(this.argumentNames[i], i);
    }

    // Check that returning and throwing were in the argument names list if
    // specified, and find the discovered argument types.
    //如果是@AfterReturning注解的returningName 有值，验证，解析，同时得到定义返回值的类型
    if (this.returningName != null) {
        if (!this.argumentBindings.containsKey(this.returningName)) {
            throw new IllegalStateException("Returning argument name '" + this.returningName +
                    "' was not bound in advice arguments");
        }
        else {
            Integer index = this.argumentBindings.get(this.returningName);
            this.discoveredReturningType = this.aspectJAdviceMethod.getParameterTypes()[index];
            this.discoveredReturningGenericType = this.aspectJAdviceMethod.getGenericParameterTypes()[index];
        }
    }
    //如果是@AfterThrowing注解的throwingName 有值，验证，解析，同时得到抛出异常的类型
    if (this.throwingName != null) {
        if (!this.argumentBindings.containsKey(this.throwingName)) {
            throw new IllegalStateException("Throwing argument name '" + this.throwingName +
                    "' was not bound in advice arguments");
        }
        else {
            Integer index = this.argumentBindings.get(this.throwingName);
            this.discoveredThrowingType = this.aspectJAdviceMethod.getParameterTypes()[index];
        }
    }

    // configure the pointcut expression accordingly.
    configurePointcutParameters(argumentIndexOffset);
}

private void configurePointcutParameters(int argumentIndexOffset) {
    int numParametersToRemove = argumentIndexOffset;
    if (this.returningName != null) {
        numParametersToRemove++;
    }
    if (this.throwingName != null) {
        numParametersToRemove++;
    }
    String[] pointcutParameterNames = new String[this.argumentNames.length - numParametersToRemove];
    Class<?>[] pointcutParameterTypes = new Class<?>[pointcutParameterNames.length];
    Class<?>[] methodParameterTypes = this.aspectJAdviceMethod.getParameterTypes();

    int index = 0;
    for (int i = 0; i < this.argumentNames.length; i++) {
        if (i < argumentIndexOffset) {
            continue;
        }
        if (this.argumentNames[i].equals(this.returningName) ||
            this.argumentNames[i].equals(this.throwingName)) {
            continue;
        }
        pointcutParameterNames[index] = this.argumentNames[i];
        pointcutParameterTypes[index] = methodParameterTypes[i];
        index++;
    }
    //剩余的未绑定的参数会赋值给AspectJExpressionPointcut(表达式形式的切入点)的属性，以备后续使用
    this.pointcut.setParameterNames(pointcutParameterNames);
    this.pointcut.setParameterTypes(pointcutParameterTypes);
}