AOP源码分析--增强器查找

*PonintCut切点查找，处理

// org.springframework.aop.aspectj.annotation.ReflectiveAspectJAdvisorFactory#getAdvisor
@Override
public Advisor getAdvisor(Method candidateAdviceMethod, MetadataAwareAspectInstanceFactory aspectInstanceFactory,
      int declarationOrderInAspect, String aspectName) {

   validate(aspectInstanceFactory.getAspectMetadata().getAspectClass());
   // 获取添加了@PointCut注解的方法，得到切点表达式
   AspectJExpressionPointcut expressionPointcut = getPointcut(
         candidateAdviceMethod, aspectInstanceFactory.getAspectMetadata().getAspectClass());
   if (expressionPointcut == null) {
      return null;
   }

   return new InstantiationModelAwarePointcutAdvisorImpl(expressionPointcut, candidateAdviceMethod,
         this, aspectInstanceFactory, declarationOrderInAspect, aspectName);
}

根据pointcut的表达式，解析真正的切点。包括：方法，|，& 等的解析。由checkReadyToMatch方法可以知道，增强器表达式是懒加载的，在调用 findAdvisorsThatCanApply(..)的时候，才会解析ecpression字符串，得到真正的切点。

// org.springframework.aop.aspectj.AspectJExpressionPointcut#checkReadyToMatch
// 检查此切入点是否已准备好匹配，从而延迟构建基础的AspectJ切入点表达式。
private void checkReadyToMatch() {
   if (getExpression() == null) {
      throw new IllegalStateException("Must set property 'expression' before attempting to match");
   }
   if (this.pointcutExpression == null) {
      this.pointcutClassLoader = determinePointcutClassLoader();
      this.pointcutExpression = buildPointcutExpression(this.pointcutClassLoader);
   }
}

/**
 *@see org.springframework.aop.framework.autoproxy.AbstractAdvisorAutoProxyCreator#findEligibleAdvisors
 */
protected List<Advisor> findEligibleAdvisors(Class<?> beanClass, String beanName) {
   //查找 Advisor 增强器，在切面上添加对应的增强操作
   List<Advisor> candidateAdvisors = findCandidateAdvisors();
   //在所有的增强器中 查找指定bean适配的增强器
   List<Advisor> eligibleAdvisors = findAdvisorsThatCanApply(candidateAdvisors, beanClass, beanName);
   extendAdvisors(eligibleAdvisors);
   if (!eligibleAdvisors.isEmpty()) {
      eligibleAdvisors = sortAdvisors(eligibleAdvisors);
   }
   return eligibleAdvisors;
}