Spring getBean

Spring的getBean

一、先看類圖

 

而後getBean來自AbstractBeanFactory類的方法

@Override
public Object getBean(String name) throws BeansException {
   return doGetBean(name, null, null, false);
}

protected <T> T doGetBean(
      final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
      throws BeansException {

   final String beanName = transformedBeanName(name);
   //獲得beanName，先去父類SimpleAliasRegistry中按照別名查找 （真是設計的很到位，負責找別名的就是找別的的，負責註冊就是註冊的，接口單一化很到位呀）
   protected String transformedBeanName(String name) {
     return canonicalName(BeanFactoryUtils.transformedBeanName(name));
   } 
  public class SimpleAliasRegistry implements AliasRegistry {

   /** Map from alias to canonical name */
   private final Map<String, String> aliasMap = new ConcurrentHashMap<String, String>(16);


   @Override
   public boolean isAlias(String name) {
      return this.aliasMap.containsKey(name);
   }
   /**
    * Determine the raw name, resolving aliases to canonical names.
    * @param name the user-specified name
    * @return the transformed name
    */
   public String canonicalName(String name) {
      String canonicalName = name;
      // Handle aliasing...
      String resolvedName;
      do {
         resolvedName = this.aliasMap.get(canonicalName);
         if (resolvedName != null) {
            canonicalName = resolvedName;
         }
      }
      while (resolvedName != null);
      return canonicalName;
   }

}

Object bean;

   // Eagerly check singleton cache for manually registered singletons.
   Object sharedInstance = getSingleton(beanName);

   //到父類DefaultSingletonBeanRegistry的getSingleton按照單利獲取實例   
 
  @Override
  public Object getSingleton(String beanName) {
     return getSingleton(beanName, true);
  }
  protected Object getSingleton(String beanName, boolean allowEarlyReference) {
  //private final Map<String, Object> singletonObjects = new ConcurrentHashMap<String, Object>(256)
     Object singletonObject = this.singletonObjects.get(beanName);
        if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
        synchronized (this.singletonObjects) {
           singletonObject = this.earlySingletonObjects.get(beanName);
           if (singletonObject == null && allowEarlyReference) {
              ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
              if (singletonFactory != null) {
                 singletonObject = singletonFactory.getObject();
                 this.earlySingletonObjects.put(beanName, singletonObject);
                 this.singletonFactories.remove(beanName);
              }
           }
        }
     }
   return (singletonObject != NULL_OBJECT ? singletonObject : null);
}

 

if (sharedInstance != null && args == null) {
      if (logger.isDebugEnabled()) {
         if (isSingletonCurrentlyInCreation(beanName)) {
            logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +
                  "' that is not fully initialized yet - a consequence of a circular reference");
         }
         else {
            logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
         }
      }
      bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
   }

   else {
       //------------------------------------------------------
      //-------------------------------前面都沒有得到到，準備建立實例
      // Fail if we're already creating this bean instance:
      // We're assumably within a circular reference.
      //確信該類沒有在建立中
      if (isPrototypeCurrentlyInCreation(beanName)) {
         protected boolean isPrototypeCurrentlyInCreation(String beanName) {
           Object curVal = this.prototypesCurrentlyInCreation.get();
           return (curVal != null &&
              (curVal.equals(beanName) || (curVal instanceof Set && ((Set<?>) curVal).contains(beanName))));
         }

         throw new BeanCurrentlyInCreationException(beanName);
      }

      // Check if bean definition exists in this factory.
      //檢查是否存在與父類的工廠中
      BeanFactory parentBeanFactory = getParentBeanFactory();
      if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
         // Not found -> check parent.
         String nameToLookup = originalBeanName(name);
         if (args != null) {
            // Delegation to parent with explicit args.
            return (T) parentBeanFactory.getBean(nameToLookup, args);
         }
         else {
            // No args -> delegate to standard getBean method.
            return parentBeanFactory.getBean(nameToLookup, requiredType);
         }
      }
      //若是父類中依舊中沒有標記該類在建立中，開始建立
      if (!typeCheckOnly) {
         markBeanAsCreated(beanName);
      }
protected void markBeanAsCreated(String beanName) {
   if (!this.alreadyCreated.contains(beanName)) {
      this.alreadyCreated.add(beanName);

      // Let the bean definition get re-merged now that we're actually creating
      // the bean... just in case some of its metadata changed in the meantime.
      clearMergedBeanDefinition(beanName);
   }
}
protected void clearMergedBeanDefinition(String beanName) {
   this.mergedBeanDefinitions.remove(beanName);
}

 

try {
         final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
         checkMergedBeanDefinition(mbd, beanName, args);
      
         // Guarantee initialization of beans that the current bean depends on.
         //獲取依賴
         String[] dependsOn = mbd.getDependsOn();
         if (dependsOn != null) {
            for (String dependsOnBean : dependsOn) {
               if (isDependent(beanName, dependsOnBean)) {
                  throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                        "Circular depends-on relationship between '" + beanName + "' and '" + dependsOnBean + "'");
               } 
               //註冊依賴
               registerDependentBean(dependsOnBean, beanName);
              //建立依賴bean
               getBean(dependsOnBean);
            }
         }

         // Create bean instance.
         //是不是單利對象
         if (mbd.isSingleton()) {
            //調用DefaultSingletonBeanRegistry getSingleton
            sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
               @Override
               public Object getObject() throws BeansException {
                  try {
                     return createBean(beanName, mbd, args);
                  }
                  catch (BeansException ex) {
                     // Explicitly remove instance from singleton cache: It might have been put there
                     // eagerly by the creation process, to allow for circular reference resolution.
                     // Also remove any beans that received a temporary reference to the bean.
                     destroySingleton(beanName);
                     throw ex;
                  }
               }
            });

        //DefaultSingletonBeanRegistry 
public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
   Assert.notNull(beanName, "'beanName' must not be null");
   synchronized (this.singletonObjects) {
      //從本地的建立好的單利map中取值
      Object singletonObject = this.singletonObjects.get(beanName);
      if (singletonObject == null) {
         if (this.singletonsCurrentlyInDestruction) {
            throw new BeanCreationNotAllowedException(beanName,
                  "Singleton bean creation not allowed while the singletons of this factory are in destruction " +
                  "(Do not request a bean from a BeanFactory in a destroy method implementation!)");
         }
         if (logger.isDebugEnabled()) {
            logger.debug("Creating shared instance of singleton bean '" + beanName + "'");
         }
         beforeSingletonCreation(beanName);
         boolean newSingleton = false;
         boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
         if (recordSuppressedExceptions) {
            this.suppressedExceptions = new LinkedHashSet<Exception>();
         }
         try {
            //回調傳入的singletonFactory建立實體類,因而又回到了上述方法的createBean
            

//AbstractAutowireCapableBeanFactory

protected Object createBean(String beanName, RootBeanDefinition mbd, Object[] args) throws BeanCreationException {
   if (logger.isDebugEnabled()) {
      logger.debug("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.
   //先獲取Class
   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.
      //獲取對應的BeanPostProcessor對象
      Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
      

protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
   Object bean = null;
   if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
      // Make sure bean class is actually resolved at this point.
      if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
         Class<?> targetType = determineTargetType(beanName, mbd);
         if (targetType != null) {
          //若是有BeanPostProcessor則調用BeanPostProcessorsBefore
            bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
            if (bean != null) {
          //若是有BeanPostProcessor則調用BeanPostProcessorsBefore
               bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
            }
         }
      }
      mbd.beforeInstantiationResolved = (bean != null);
   }
  //最終返回對應的BeanPostProcessor對象
   return bean;
}

      if (bean != null) {
         return bean;
      }
   }
   catch (Throwable ex) {
      throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,
            "BeanPostProcessor before instantiation of bean failed", ex);
   }
   //繼續建立
   Object beanInstance = doCreateBean(beanName, mbdToUse, args);
   

protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, Object[] args) {
   // Make sure bean class is actually resolved at this point.
   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());
   }
   //有就建立這個類的工廠類
   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;
         }
      }
   }
   if (resolved) {
      if (autowireNecessary) {
         return autowireConstructor(beanName, mbd, null, null);
      }
      else {
         return instantiateBean(beanName, mbd);
      }
   }

   // Need to determine the constructor...
   //查找這個bean的BeanPostProcessor構造器
   Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
   if (ctors != null ||
         mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_CONSTRUCTOR ||
         mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args))  {
      return autowireConstructor(beanName, mbd, ctors, args);
   }

   // No special handling: simply use no-arg constructor.
   return instantiateBean(beanName, mbd);
}

protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) {
   // Instantiate the bean.
   BeanWrapper instanceWrapper = null;
   if (mbd.isSingleton()) {
      instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
   }
   if (instanceWrapper == null) {
      instanceWrapper = createBeanInstance(beanName, mbd, args);
   }
   final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
   Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);

   // Allow post-processors to modify the merged bean definition.
   synchronized (mbd.postProcessingLock) {
      if (!mbd.postProcessed) {
         applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
         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.isDebugEnabled()) {
         logger.debug("Eagerly caching bean '" + beanName +
               "' to allow for resolving potential circular references");
      }
      addSingletonFactory(beanName, new ObjectFactory<Object>() {
         @Override
         public Object getObject() throws BeansException {
            return getEarlyBeanReference(beanName, mbd, bean);
         }
      });
   }

   // Initialize the bean instance.
   Object exposedObject = bean;
   try {
      populateBean(beanName, mbd, instanceWrapper);
      if (exposedObject != null) {
         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<String>(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 " +
                     "'getBeanNamesOfType' 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;
}

  
   if (logger.isDebugEnabled()) {
      logger.debug("Finished creating instance of bean '" + beanName + "'");
   }
   return beanInstance;
}

 

 

            singletonObject = singletonFactory.getObject();
            newSingleton = true;
         }
         catch (IllegalStateException ex) {
            // Has the singleton object implicitly appeared in the meantime ->
            // if yes, proceed with it since the exception indicates that state.
            singletonObject = this.singletonObjects.get(beanName);
            if (singletonObject == null) {
               throw ex;
            }
         }
         catch (BeanCreationException ex) {
            if (recordSuppressedExceptions) {
               for (Exception suppressedException : this.suppressedExceptions) {
                  ex.addRelatedCause(suppressedException);
               }
            }
            throw ex;
         }
         finally {
            if (recordSuppressedExceptions) {
               this.suppressedExceptions = null;
            }
            afterSingletonCreation(beanName);
         }
         if (newSingleton) {
            addSingleton(beanName, singletonObject);
         }
      }
      return (singletonObject != NULL_OBJECT ? singletonObject : null);
   }
}

bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
         }

         else if (mbd.isPrototype()) {
            // It's a prototype -> create a new instance.
            Object prototypeInstance = null;
            try {
               //這步通知
               beforePrototypeCreation(beanName);
               prototypeInstance = createBean(beanName, mbd, args);
            }
            finally {
               afterPrototypeCreation(beanName);
            }
            bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
         }

         else {
            String scopeName = mbd.getScope();
            final Scope scope = this.scopes.get(scopeName);
            if (scope == null) {
               throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
            }
            try {
               Object scopedInstance = scope.get(beanName, new ObjectFactory<Object>() {
                  @Override
                  public Object getObject() throws BeansException {
                     beforePrototypeCreation(beanName);
                     try {
                        return createBean(beanName, mbd, args);
                     }
                     finally {
                        afterPrototypeCreation(beanName);
                     }
                  }
               });
               bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
            }
            catch (IllegalStateException ex) {
               throw new BeanCreationException(beanName,
                     "Scope '" + scopeName + "' is not active for the current thread; consider " +
                     "defining a scoped proxy for this bean if you intend to refer to it from a singleton",
                     ex);
            }
         }
      }
      catch (BeansException ex) {
         cleanupAfterBeanCreationFailure(beanName);
         throw ex;
      }
   }

   // Check if required type matches the type of the actual bean instance.
   if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
      try {
         return getTypeConverter().convertIfNecessary(bean, requiredType);
      }
      catch (TypeMismatchException ex) {
         if (logger.isDebugEnabled()) {
            logger.debug("Failed to convert bean '" + name + "' to required type [" +
                  ClassUtils.getQualifiedName(requiredType) + "]", ex);
         }
         throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
      }
   }
   return (T) bean;
}