Springframework之ReflectiveAspectJAdvisorFactory

    Spring版本是5.0.4.release.

    ReflectiveAspectJAdvisorFactory这个类，个人觉得是Spring aop的一个核心类。如下List-1所示，ReflectiveAspectJAdvisorFactory间接实现了AspectJAdvisorFactory。

    List-1

public interface AspectJAdvisorFactory {

	boolean isAspect(Class<?> clazz);

	void validate(Class<?> aspectClass) throws AopConfigException;

	List<Advisor> getAdvisors(MetadataAwareAspectInstanceFactory aspectInstanceFactory);

	Advisor getAdvisor(Method candidateAdviceMethod, MetadataAwareAspectInstanceFactory aspectInstanceFactory,
			int declarationOrder, String aspectName);

	Advice getAdvice(Method candidateAdviceMethod, AspectJExpressionPointcut expressionPointcut,
			MetadataAwareAspectInstanceFactory aspectInstanceFactory, int declarationOrder, String aspectName);
}

    List-1中的isAspect方法判断类上是否有Aspect注解，BeanFactoryAspectJAdvisorsBuilder就用这个方法判断一个类上是有Aspect注解。

    有必要来看下AbstractAspectJAdvisorFactory这个类，因为ReflectiveAspectJAdvisorFactory继承了它。如下List-2所示，isAspect方法判断类上是有Aspect注解。

    List-2

public abstract class AbstractAspectJAdvisorFactory implements AspectJAdvisorFactory {

	private static final String AJC_MAGIC = "ajc$";

	private static final Class<?>[] ASPECTJ_ANNOTATION_CLASSES = new Class<?>[] {
			Pointcut.class, Around.class, Before.class, After.class, AfterReturning.class, AfterThrowing.class};

	protected final Log logger = LogFactory.getLog(getClass());

	protected final ParameterNameDiscoverer parameterNameDiscoverer = new AspectJAnnotationParameterNameDiscoverer();

	@Override
	public boolean isAspect(Class<?> clazz) {
		return (hasAspectAnnotation(clazz) && !compiledByAjc(clazz));
	}

	private boolean hasAspectAnnotation(Class<?> clazz) {
		return (AnnotationUtils.findAnnotation(clazz, Aspect.class) != null);
	}
...

    如下List-3所示，这个类还有个工具方法，查看方法上面是否有Pointcut.class, Around.class, Before.class, After.class, AfterReturning.class, AfterThrowing.class注解，如果找到一个，则封装为AspectJAnnotation返回。 

  List-3

@Nullable
protected static AspectJAnnotation<?> findAspectJAnnotationOnMethod(Method method) {
  for (Class<?> clazz : ASPECTJ_ANNOTATION_CLASSES) {
    AspectJAnnotation<?> foundAnnotation = findAnnotation(method, (Class<Annotation>) clazz);
    if (foundAnnotation != null) {
      return foundAnnotation;
    }
  }
  return null;
}

@Nullable
private static <A extends Annotation> AspectJAnnotation<A> findAnnotation(Method method, Class<A> toLookFor) {
  A result = AnnotationUtils.findAnnotation(method, toLookFor);
  if (result != null) {
    return new AspectJAnnotation<>(result);
  }
  else {
    return null;
  }
}

    ReflectiveAspectJAdvisorFactory的getAdvice方法会根据方法上的注解，创建对应的Advice，如下List-4所示

    List-4

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

  AbstractAspectJAdvice springAdvice;
  ...
  switch (aspectJAnnotation.getAnnotationType()) {
    case AtPointcut:
      if (logger.isDebugEnabled()) {
        logger.debug("Processing pointcut '" + candidateAdviceMethod.getName() + "'");
      }
      return null;
    case AtAround:
      springAdvice = new AspectJAroundAdvice(
          candidateAdviceMethod, expressionPointcut, aspectInstanceFactory);
      break;
    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;
    default:
      throw new UnsupportedOperationException(
          "Unsupported advice type on method: " + candidateAdviceMethod);
  }
...

Reference

1. https://github.com/spring-projects/spring-framework/tree/5.0.x