spring源码分析2

AbstractApplicationContext#refresh方法的finishBeanFactoryInitialization方法,实例化bean

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
   // Initialize conversion service for this context.
   if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
         beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
      beanFactory.setConversionService(
            beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
   }

   // Register a default embedded value resolver if no bean post-processor
   // (such as a PropertyPlaceholderConfigurer bean) registered any before:
   // at this point, primarily for resolution in annotation attribute values.
   if (!beanFactory.hasEmbeddedValueResolver()) {
      beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
   }

   // Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
   String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
   for (String weaverAwareName : weaverAwareNames) {
      getBean(weaverAwareName);
   }

   // Stop using the temporary ClassLoader for type matching.
   beanFactory.setTempClassLoader(null);

   // Allow for caching all bean definition metadata, not expecting further changes.
//冻结bean,就是将beanFactory的configurationFrozen属性设置为true,不允许修改beanDefinition
   beanFactory.freezeConfiguration();

   // Instantiate all remaining (non-lazy-init) singletons.
   beanFactory.preInstantiateSingletons();
}



@Override
public void preInstantiateSingletons() throws BeansException {
   if (logger.isTraceEnabled()) {
      logger.trace("Pre-instantiating singletons in " + this);
   }

   // Iterate over a copy to allow for init methods which in turn register new bean definitions.
   // While this may not be part of the regular factory bootstrap, it does otherwise work fine.
   List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);

   // Trigger initialization of all non-lazy singleton beans...
//获取所有BeanDefinition的名称
   for (String beanName : beanNames) {
//通过@bean @import @configuration 等存入的beanDefintionMap的value是不同的,但都是BeanDefinition的子类,这里通过名字循环,并用下面的代码都转为RootBeanDefinition①
      RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
//判断不是抽象类 是单例 不是懒加载
      if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
//判断是否是FactoryBean的实现类
         if (isFactoryBean(beanName)) {
//如果是,获取实现FacrotyBean类本身,( FacrotyBean类实现类获取bean是getObject方法的返回值), FACTORY_BEAN_PREFIX 为& 
            Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
            if (bean instanceof FactoryBean) {
               FactoryBean<?> factory = (FactoryBean<?>) bean;
               boolean isEagerInit;
               if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
                  isEagerInit = AccessController.doPrivileged(
                        (PrivilegedAction<Boolean>) ((SmartFactoryBean<?>) factory)::isEagerInit,
                        getAccessControlContext());
               }
               else {
                  isEagerInit = (factory instanceof SmartFactoryBean &&
                        ((SmartFactoryBean<?>) factory).isEagerInit());
               }
               if (isEagerInit) {
// getBean方法中会判断beanName类是否实现了FactoryBean,实现了则调用getObject方法
//通过AbstractBeanFactory#doGetBean的
//bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
//代码调用的getObject()方法
                  getBean(beanName);
               }
            }
         }
         else {
            getBean(beanName);
         }
      }
   }

   // Trigger post-initialization callback for all applicable beans...
   for (String beanName : beanNames) {
      Object singletonInstance = getSingleton(beanName);
      if (singletonInstance instanceof SmartInitializingSingleton) {
         StartupStep smartInitialize = this.getApplicationStartup().start("spring.beans.smart-initialize")
               .tag("beanName", beanName);
         SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
         if (System.getSecurityManager() != null) {
            AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
               smartSingleton.afterSingletonsInstantiated();
               return null;
            }, getAccessControlContext());
         }
         else {
            smartSingleton.afterSingletonsInstantiated();
         }
         smartInitialize.end();
      }
   }
}

① BeanDefinitionMap的value为不同的类型的beanDefinition
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AbstractFacrotyBean#doGetBean方法

protected <T> T doGetBean(
      String name, @Nullable Class<T> requiredType, @Nullable Object[] args, boolean typeCheckOnly)
      throws BeansException {
//如果是别名则返回beanDefinitionMap中key的名称,并且去掉FactoryBean用到的&
//何为别名,@Bean(name) @Bean(name={"tank","tankAlias"}) tank为beanDefinitionMap中的名称, tankAlias为别名,通过tankAlias得到的是tank
   String beanName = transformedBeanName(name);
   Object bean;

   // Eagerly check singleton cache for manually registered singletons.
//从一级缓存中获取,如果是第一次调用,缓存中不会存在, getSingleton方法利用三级缓存解决循环依赖问题,后续会分析
   Object sharedInstance = getSingleton(beanName);
   if (sharedInstance != null && args == null) {
      if (logger.isTraceEnabled()) {
         if (isSingletonCurrentlyInCreation(beanName)) {
            logger.trace("Returning eagerly cached instance of singleton bean '" + beanName +
                  "' that is not fully initialized yet - a consequence of a circular reference");
         }
         else {
            logger.trace("Returning cached instance of singleton bean '" + beanName + "'");
         }
      }
//如果类实现FacrotyBean则在这里调用getObject()方法,返回Bean
      bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
   }

   else {
      // Fail if we're already creating this bean instance:
      // We're assumably within a circular reference.
//如果是多例bean会抛出异常
      if (isPrototypeCurrentlyInCreation(beanName)) {
         throw new BeanCurrentlyInCreationException(beanName);
      }
//父容器,这里不做分析,后续会分析到
      // Check if bean definition exists in this factory.
      BeanFactory parentBeanFactory = getParentBeanFactory();
      if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
         // Not found -> check parent.
         String nameToLookup = originalBeanName(name);
         if (parentBeanFactory instanceof AbstractBeanFactory) {
            return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
                  nameToLookup, requiredType, args, typeCheckOnly);
         }
         else if (args != null) {
            // Delegation to parent with explicit args.
            return (T) parentBeanFactory.getBean(nameToLookup, args);
         }
         else if (requiredType != null) {
            // No args -> delegate to standard getBean method.
            return parentBeanFactory.getBean(nameToLookup, requiredType);
         }
         else {
            return (T) parentBeanFactory.getBean(nameToLookup);
         }
      }

      if (!typeCheckOnly) {
// 将beanName放到alreadyCreated成员变量中,代表马上就要创建
         markBeanAsCreated(beanName);
      }

      StartupStep beanCreation = this.applicationStartup.start("spring.beans.instantiate")
            .tag("beanName", name);
      try {
         if (requiredType != null) {
            beanCreation.tag("beanType", requiredType::toString);
         }
         RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
//检查当前创建的bean定义是不是抽象的bean定义
         checkMergedBeanDefinition(mbd, beanName, args);

         // Guarantee initialization of beans that the current bean depends on.
//在上一篇文章中分析解析类的时候将@DependsOn注解将要依赖的Bean名称,放到beanDefinition的dependsOn成员变量中,这里获取出来
// ClassPathBeanDefinitionScanner# doScan的//AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition//) candidate);方法注入的, processCommonDefinitionAnnotations方法还注入了很多注解//Lazy
//Primary Role Description等
         String[] dependsOn = mbd.getDependsOn();
         if (dependsOn != null) {
            for (String dep : dependsOn) {
               if (isDependent(beanName, dep)) {
                  throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                        "Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
               }
               registerDependentBean(dep, beanName);
               try {
//getBean当前类之前,先getBean dependsOn中的类,这里的dep是dependsOn
                  getBean(dep);
               }
               catch (NoSuchBeanDefinitionException ex) {
                  throw new BeanCreationException(mbd.getResourceDescription(), beanName,  "'" + beanName + "' depends on missing bean '" + dep + "'", ex);
               }
            }
         }

         // Create bean instance.
//如果bean是单例
         if (mbd.isSingleton()) {
// getSingleton的主要作用就是赋值bean正在创建状态,并传一个回调函数,lambda表达式
// createBean此时创建bean
            sharedInstance = getSingleton(beanName, () -> {
               try {
//createBean方法,创建Bean的主要方法
                  return createBean(beanName, mbd, args);
               }
   ……………………省略的代码
   return (T) bean;
}

AbstractAutowireCapableBeanFactory#createBean方法

@Override
protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
      throws BeanCreationException {

   if (logger.isTraceEnabled()) {
      logger.trace("Creating instance of bean '" + beanName + "'");
   }
   RootBeanDefinition mbdToUse = mbd;

   // Make sure bean class is actually resolved at this point, and
   // clone the bean definition in case of a dynamically resolved Class
   // which cannot be stored in the shared merged bean definition.
   Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
   if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
      mbdToUse = new RootBeanDefinition(mbd);
      mbdToUse.setBeanClass(resolvedClass);
   }

   // Prepare method overrides.
   try {
      mbdToUse.prepareMethodOverrides();
   }
   catch (BeanDefinitionValidationException ex) {
      throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
            beanName, "Validation of method overrides failed", ex);
   }

   try {
      // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
//调用第一个Bean的后置处理器InstantiationAwareBeanPostProcessor,项目中不经常使用这个后置处理器,可以返回任意的bean,比如beanName是car,返回值可以返回Tank
      Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
//如果bean不为null,直接返回了,创建Bean结束了,这是唯一一个可以直接返回Bean的后置处理器
      if (bean != null) {
         return bean;
      }
   }
   catch (Throwable ex) {
      throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,
            "BeanPostProcessor before instantiation of bean failed", ex);
   }

   try {
//如果resolveBeforeInstantiation(beanName, mbdToUse)返回null,那真正创建Bean的方法来了
      Object beanInstance = doCreateBean(beanName, mbdToUse, args);
      if (logger.isTraceEnabled()) {
         logger.trace("Finished creating instance of bean '" + beanName + "'");
      }
      return beanInstance;
   }
   catch (BeanCreationException | ImplicitlyAppearedSingletonException ex) {
      // A previously detected exception with proper bean creation context already,
      // or illegal singleton state to be communicated up to DefaultSingletonBeanRegistry.
      throw ex;
   }
   catch (Throwable ex) {
      throw new BeanCreationException(
            mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", ex);
   }
}

AbstractAutowireCapableBeanFacroty#doCreateBean真正创建bean方法

protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
      throws BeanCreationException {

   // Instantiate the bean.
//bean的包装类
   BeanWrapper instanceWrapper = null;
   if (mbd.isSingleton()) {
      instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
   }
   if (instanceWrapper == null) {
//创建Bean的关键方法,通过构造函数创建,如果构造函数有入参的话,从容器中取出,并赋值,
非构造函数入参的成员变量,即使@Autowire标注,也不会赋值,后续代码会赋值
//这里也就看出了,三级缓存不能解决构造函数的循环依赖
      instanceWrapper = createBeanInstance(beanName, mbd, args);
   }
//获取bean
   Object bean = instanceWrapper.getWrappedInstance();
   Class<?> beanType = instanceWrapper.getWrappedClass();
   if (beanType != NullBean.class) {
      mbd.resolvedTargetType = beanType;
   }

   // Allow post-processors to modify the merged bean definition.
   synchronized (mbd.postProcessingLock) {
      if (!mbd.postProcessed) {
         try {
//进行后置处理 @AutoWired @Value@Resource的注解的预解析,此时预解析存放在
// 方法会遍历InstantiationAwareBeanPostProcessor的实现类的postProcessMergedBeanDefinition方法
//AutowiredAnnotationBeanPostProcessor预解析, @Autowired和@value标注的成员变量
//CommonAnnotationBeanPostProcessor预解析@Resource标注的成员变量
//预解析就是将标注@AutoWired @Value@Resource的类放到成员变量injectionMetadataCache
中,再下面populateBean方法中遍历后置处理器执行postProcessProperties方法,会从injectionMetadataCache取出并赋值
//这里只是预解析,并没有赋值
            applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
         }
         catch (Throwable ex) {
            throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                  "Post-processing of merged bean definition failed", ex);
         }
         mbd.postProcessed = true;
      }
   }

   // Eagerly cache singletons to be able to resolve circular references
   // even when triggered by lifecycle interfaces like BeanFactoryAware.
   boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
         isSingletonCurrentlyInCreation(beanName));
   if (earlySingletonExposure) {
      if (logger.isTraceEnabled()) {
         logger.trace("Eagerly caching bean '" + beanName +
               "' to allow for resolving potential circular references");
      }
      addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
   }

   // Initialize the bean instance.
   Object exposedObject = bean;
   try {
//bean后置处理器,为@Autowired,@Resource,@Value赋值和xml通过type/name赋值属性,下篇文章分析
      populateBean(beanName, mbd, instanceWrapper);
//bean的后置处理器和绝大多数的aware的执行 下篇文章分析
      exposedObject = initializeBean(beanName, exposedObject, mbd);
   }
   catch (Throwable ex) {
      if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
         throw (BeanCreationException) ex;
      }
      else {
         throw new BeanCreationException(
               mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
      }
   }

   if (earlySingletonExposure) {
      Object earlySingletonReference = getSingleton(beanName, false);
      if (earlySingletonReference != null) {
         if (exposedObject == bean) {
            exposedObject = earlySingletonReference;
         }
         else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
            String[] dependentBeans = getDependentBeans(beanName);
            Set<String> actualDependentBeans = new LinkedHashSet<>(dependentBeans.length);
            for (String dependentBean : dependentBeans) {
               if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
                  actualDependentBeans.add(dependentBean);
               }
            }
            if (!actualDependentBeans.isEmpty()) {
               throw new BeanCurrentlyInCreationException(beanName,
                     "Bean with name '" + beanName + "' has been injected into other beans [" +
                     StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
                     "] in its raw version as part of a circular reference, but has eventually been " +
                     "wrapped. This means that said other beans do not use the final version of the " +
                     "bean. This is often the result of over-eager type matching - consider using " +
                     "'getBeanNamesForType' with the 'allowEagerInit' flag turned off, for example.");
            }
         }
      }
   }

   // Register bean as disposable.
   try {
      registerDisposableBeanIfNecessary(beanName, bean, mbd);
   }
   catch (BeanDefinitionValidationException ex) {
      throw new BeanCreationException(
            mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
   }

   return exposedObject;
}

createBeanInstance方法

protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
   // Make sure bean class is actually resolved at this point.
//根据beanDefinitionMap中key的名称获取beanClass 如果@Bean beanClass为null
   Class<?> beanClass = resolveBeanClass(mbd, beanName);

   if (beanClass != null && !Modifier.isPublic(beanClass.getModifiers()) && !mbd.isNonPublicAccessAllowed()) {
      throw new BeanCreationException(mbd.getResourceDescription(), beanName,
            "Bean class isn't public, and non-public access not allowed: " + beanClass.getName());
   }

   Supplier<?> instanceSupplier = mbd.getInstanceSupplier();
   if (instanceSupplier != null) {
      return obtainFromSupplier(instanceSupplier, beanName);
   }

   if (mbd.getFactoryMethodName() != null) {
      return instantiateUsingFactoryMethod(beanName, mbd, args);
   }

   // Shortcut when re-creating the same bean...
   boolean resolved = false;
   boolean autowireNecessary = false;
   if (args == null) {
      synchronized (mbd.constructorArgumentLock) {
         if (mbd.resolvedConstructorOrFactoryMethod != null) {
            resolved = true;
            autowireNecessary = mbd.constructorArgumentsResolved;
         }
      }
   }
//如果已经解析过了,就是已经确定要使用那个构造函数创建类
   if (resolved) {
//有参构造函数创建类
      if (autowireNecessary) {
         return autowireConstructor(beanName, mbd, null, null);
      }
      else {
//无参构造函数创建类
         return instantiateBean(beanName, mbd);
      }
   }

   // Candidate constructors for autowiring?
//这个方法bean的后置处理器SmartInstantiationAwareBeanPostProcessor
//这里是子类AutowiredAnnotationBeanPostProcessor
//作用是确定使用哪个构造函数创建bean,类中没有显示的构造函数,为无参构造函数,
//如果只有一个有参构造函数,默认就是这个有参构造函数
//如果有多个有参构造函数,获取标注@Autowired 的有参构造函数
   Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
   if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||
         mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
      return autowireConstructor(beanName, mbd, ctors, args);
   }

   // Preferred constructors for default construction?
   ctors = mbd.getPreferredConstructors();
   if (ctors != null) {
//有参构造函数创建类,并初始化了构造函数的入参,此时构造函数的入参被赋值,但是非入参的//成员变量,即使有@Autowire注释也不会赋值
//argsHolder = createArgumentArray(beanName, mbd, resolvedValues, bw, paramTypes, //paramNames,   getUserDeclaredConstructor(candidate), autowiring);将构造函数的入参赋值,所谓的赋值是从IOC容器中获取的bean,不是new的

      return autowireConstructor(beanName, mbd, ctors, null);
   }
//无参构造函数创建类
   // No special handling: simply use no-arg constructor.
   return instantiateBean(beanName, mbd);
}

determineCandidateConstructors实例化类可以使用的构造器

@Override
@Nullable
public Constructor<?>[] determineCandidateConstructors(Class<?> beanClass, final String beanName)
      throws BeanCreationException {
//@LookUp注解,主要作用解释一下,就是A类是单例 @AutowireB 类,但是B类是多例的,但是A在创建的时候,B就已经初始化到A类,每次使用A类时(C类D类@AutoWire A类),B类是固定的,(当然不同的类@Autowire B类是不同的) @LookUp 解决此问题,可能应用的场景不多
   // Let's check for lookup methods here...
   if (!this.lookupMethodsChecked.contains(beanName)) {
      if (AnnotationUtils.isCandidateClass(beanClass, Lookup.class)) {
         try {
            Class<?> targetClass = beanClass;
            do {
               ReflectionUtils.doWithLocalMethods(targetClass, method -> {
                  Lookup lookup = method.getAnnotation(Lookup.class);
                  if (lookup != null) {
                     Assert.state(this.beanFactory != null, "No BeanFactory available");
                     LookupOverride override = new LookupOverride(method, lookup.value());
                     try {
                        RootBeanDefinition mbd = (RootBeanDefinition)
                              this.beanFactory.getMergedBeanDefinition(beanName);
                        mbd.getMethodOverrides().addOverride(override);
                     }
                     catch (NoSuchBeanDefinitionException ex) {
                        throw new BeanCreationException(beanName,
                              "Cannot apply @Lookup to beans without corresponding bean definition");
                     }
                  }
               });
               targetClass = targetClass.getSuperclass();
            }
            while (targetClass != null && targetClass != Object.class);

         }
         catch (IllegalStateException ex) {
            throw new BeanCreationException(beanName, "Lookup method resolution failed", ex);
         }
      }
      this.lookupMethodsChecked.add(beanName);
   }

   // Quick check on the concurrent map first, with minimal locking.
//缓存是为了下次直接可以获取可以使用的构造器,能用到下段代码,我分析是在多线程下并且是多例的情况下,两个线程同时创建bean 
   Constructor<?>[] candidateConstructors = this.candidateConstructorsCache.get(beanClass);
//为null
   if (candidateConstructors == null) {
      // Fully synchronized resolution now...
      synchronized (this.candidateConstructorsCache) {
         candidateConstructors = this.candidateConstructorsCache.get(beanClass);
         if (candidateConstructors == null) {
            Constructor<?>[] rawCandidates;
            try {
//获取本类的所有构造器
               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<>(rawCandidates.length);
            Constructor<?> requiredConstructor = null;
            Constructor<?> defaultConstructor = null;
            Constructor<?> primaryConstructor = BeanUtils.findPrimaryConstructor(beanClass);
            int nonSyntheticConstructors = 0;
            for (Constructor<?> candidate : rawCandidates) {
               if (!candidate.isSynthetic()) {
                  nonSyntheticConstructors++;
               }
               else if (primaryConstructor != null) {
                  continue;
               }
//获取标注了@Autowire
               MergedAnnotation<?> ann = findAutowiredAnnotation(candidate);
               if (ann == null) {
//如果没有找到   @Autowire标注的构造器,判断是否是CGlib代理,如果是代理则获取原始类               
Class<?> userClass = ClassUtils.getUserClass(beanClass);
                  if (userClass != beanClass) {
                     try {
//获取原始类的所有构造函数
                        Constructor<?> superCtor =                              userClass.getDeclaredConstructor(candidate.getParameterTypes());
//获取原始类继续查找@Autowire标注的构造器
                        ann = findAutowiredAnnotation(superCtor);
                     }
                     catch (NoSuchMethodException ex) {
                        // Simply proceed, no equivalent superclass constructor found...
                     }
                  }
               }
//判断@Autowire 是否为require
               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);
                     }
                     requiredConstructor = candidate;
                  }
                  candidates.add(candidate);
               }
               else if (candidate.getParameterCount() == 0) {
                  defaultConstructor = candidate;
               }
            }
            if (!candidates.isEmpty()) {
               // Add default constructor to list of optional constructors, as fallback.
               if (requiredConstructor == null) {
                  if (defaultConstructor != null) {
                     candidates.add(defaultConstructor);
                  }
                  else if (candidates.size() == 1 && logger.isInfoEnabled()) {
                     logger.info("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<?>[0]);
            }
//如果就一个有参构造函数,就算没有被@Autowire标注,依然被返回,这就是我们在项目中经常将所有的成员变量放到构造函数中,也没有标注@Autowire,依然可以注入的原因
            else if (rawCandidates.length == 1 && rawCandidates[0].getParameterCount() > 0) {
               candidateConstructors = new Constructor<?>[] {rawCandidates[0]};
            }
            else if (nonSyntheticConstructors == 2 && primaryConstructor != null &&
                  defaultConstructor != null && !primaryConstructor.equals(defaultConstructor)) {
               candidateConstructors = new Constructor<?>[] {primaryConstructor, defaultConstructor};
            }
            else if (nonSyntheticConstructors == 1 && primaryConstructor != null) {
               candidateConstructors = new Constructor<?>[] {primaryConstructor};
            }
            else {
               candidateConstructors = new Constructor<?>[0];
            }
            this.candidateConstructorsCache.put(beanClass, candidateConstructors);
         }
      }
   }
//返回需要的构造器
   return (candidateConstructors.length > 0 ? candidateConstructors : null);
}

AbstractAutowireCapableBeanFacroty#doCreateBean的populateBean和exposedObject两个主要的方法下篇文章继续分析