Spring注解Autowired的底层实现原理详解

private InjectionMetadata buildAutowiringMetadata(final Class<?> clazz) {
  LinkedList<InjectionMetadata.InjectedElement> elements = new LinkedList<>();
  Class<?> targetClass = clazz;//需要处理的目标类
       
  do {
   final LinkedList<InjectionMetadata.InjectedElement> currElements = new LinkedList<>();
 
            /*通过反射获取该类所有的字段，并遍历每一个字段，并通过方法findAutowiredAnnotation遍历每一个字段的所用注解，并如果用autowired修饰了，则返回auotowired相关属性*/  
 
   ReflectionUtils.doWithLocalFields(targetClass, field -> {
    AnnotationAttributes ann = findAutowiredAnnotation(field);
    if (ann != null) {//校验autowired注解是否用在了static方法上
     if (Modifier.isStatic(field.getModifiers())) {
      if (logger.isWarnEnabled()) {
       logger.warn("Autowired annotation is not supported on static fields: " + field);
      }
      return;
     }//判断是否指定了required
     boolean required = determineRequiredStatus(ann);
     currElements.add(new AutowiredFieldElement(field, required));
    }
   });
            //和上面一样的逻辑，但是是通过反射处理类的method
   ReflectionUtils.doWithLocalMethods(targetClass, method -> {
    Method bridgedMethod = BridgeMethodResolver.findBridgedMethod(method);
    if (!BridgeMethodResolver.isVisibilityBridgeMethodPair(method, bridgedMethod)) {
     return;
    }
    AnnotationAttributes ann = findAutowiredAnnotation(bridgedMethod);
    if (ann != null && method.equals(ClassUtils.getMostSpecificMethod(method, clazz))) {
     if (Modifier.isStatic(method.getModifiers())) {
      if (logger.isWarnEnabled()) {
       logger.warn("Autowired annotation is not supported on static methods: " + method);
      }
      return;
     }
     if (method.getParameterCount() == 0) {
      if (logger.isWarnEnabled()) {
       logger.warn("Autowired annotation should only be used on methods with parameters: " +
         method);
      }
     }
     boolean required = determineRequiredStatus(ann);
     PropertyDescriptor pd = BeanUtils.findPropertyForMethod(bridgedMethod, clazz);
                   currElements.add(new AutowiredMethodElement(method, required, pd));
    }
   });
    //用@Autowired修饰的注解可能不止一个，因此都加在currElements这个容器里面，一起处理  
   elements.addAll(0, currElements);
   targetClass = targetClass.getSuperclass();
  }
  while (targetClass != null && targetClass != Object.class);
 
  return new InjectionMetadata(clazz, elements);
 }