Spring 推断构造方法

方法：org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor#determineCandidateConstructors

 

org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor#determineCandidateConstructors

// Quick check on the concurrent map first, with minimal locking.
Constructor<?>[] candidateConstructors = this.candidateConstructorsCache.get(beanClass);
if (candidateConstructors == null) {
   // Fully synchronized resolution now...
   synchronized (this.candidateConstructorsCache) {
      candidateConstructors = this.candidateConstructorsCache.get(beanClass);
      if (candidateConstructors == null) {
         Constructor<?>[] rawCandidates;
         try {
//获取该class中的构造方法
            rawCandidates = beanClass.getDeclaredConstructors();
         }
         catch (Throwable ex) {
            throw new BeanCreationException(beanName,
                  "Resolution of declared constructors on bean Class [" + beanClass.getName() +
                  "] from ClassLoader [" + beanClass.getClassLoader() + "] failed", ex);
         }
         List<Constructor<?>> candidates = new ArrayList<Constructor<?>>(rawCandidates.length);
         Constructor<?> requiredConstructor = null;
         Constructor<?> defaultConstructor = null;
         for (Constructor<?> candidate : rawCandidates) {
//在构造方法上查看是否有@Autowired
            AnnotationAttributes ann = findAutowiredAnnotation(candidate);
            if (ann == null) {
               Class<?> userClass = ClassUtils.getUserClass(beanClass);
               if (userClass != beanClass) {
                  try {
                     Constructor<?> superCtor =
                           userClass.getDeclaredConstructor(candidate.getParameterTypes());
                     ann = findAutowiredAnnotation(superCtor);
                  }
                  catch (NoSuchMethodException ex) {
                     // Simply proceed, no equivalent superclass constructor found...
                  }
               }
            }
            if (ann != null) {
               if (requiredConstructor != null) {
                  throw new BeanCreationException(beanName,
                        "Invalid autowire-marked constructor: " + candidate +
                        ". Found constructor with 'required' Autowired annotation already: " +
                        requiredConstructor);
               }
               boolean required = determineRequiredStatus(ann);
               if (required) {
                  if (!candidates.isEmpty()) {
                     throw new BeanCreationException(beanName,
                           "Invalid autowire-marked constructors: " + candidates +
                           ". Found constructor with 'required' Autowired annotation: " +
                           candidate);
                  }
　　　　　　　　　　　//1.如果既有@Autowired ，required=true。则赋值给requiredConstructor 
                  requiredConstructor = candidate;
               }
　　　　　　　　　//并添加到candidates
               candidates.add(candidate);
            }
            else if (candidate.getParameterTypes().length == 0) {
               defaultConstructor = candidate;
            }
         }
         if (!candidates.isEmpty()) {
            // Add default constructor to list of optional constructors, as fallback.
            if (requiredConstructor == null) {
               if (defaultConstructor != null) {
　　　　　　　　　　 //2.如果只有默认，没有required=true ，也添加到candidates
                  candidates.add(defaultConstructor);
               }
               else if (candidates.size() == 1 && logger.isWarnEnabled()) {
                  logger.warn("Inconsistent constructor declaration on bean with name '" + beanName +
                        "': single autowire-marked constructor flagged as optional - " +
                        "this constructor is effectively required since there is no " +
                        "default constructor to fall back to: " + candidates.get(0));
               }
            }
            candidateConstructors = candidates.toArray(new Constructor<?>[candidates.size()]);
         }
　　　　　//3.如果该方法只有一个构造方法。并且参数大于零。也把他加入candidates
         else if (rawCandidates.length == 1 && rawCandidates[0].getParameterTypes().length > 0) {
            candidateConstructors = new Constructor<?>[] {rawCandidates[0]};
         }
         else {
　　　　　　　//4.否则就没有构造方法。
            candidateConstructors = new Constructor<?>[0];
         }
         this.candidateConstructorsCache.put(beanClass, candidateConstructors);
      }
   }
}
return (candidateConstructors.length > 0 ? candidateConstructors : null);