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《Spring源码深度解析(第2版)》

版本

本文章基于 Spring 5.3.15

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前面实现了 ClassPathXmlApplicationContext 的构造，接下来分析其调用的 getBean 方法。

以 getBean(UserDao.class) 为例。

1 AbstractApplicationContext

public 
    
      T getBean(Class
     
       requiredType) throws BeansException {    // 断言 Bean 工厂活动    assertBeanFactoryActive();    // 获取 Bean 工厂    // 获取 Bean    return getBeanFactory().getBean(requiredType);}
     
    

1-1 断言 Bean 工厂活动

assertBeanFactoryActive()

protected void assertBeanFactoryActive() {   if (!this.active.get()) {      if (this.closed.get()) {         // 获取显示名称         throw new IllegalStateException(getDisplayName() + " has been closed already");      }      else {         // 获取显示名称         throw new IllegalStateException(getDisplayName() + " has not been refreshed yet");      }   }}

获取显示名称前面已经分析过了，这里不再分析。

1-1 获取 Bean 工厂

getBeanFactory()

2 AbstractRefreshableApplicationContext

public final ConfigurableListableBeanFactory getBeanFactory() {   DefaultListableBeanFactory beanFactory = this.beanFactory;   if (beanFactory == null) {      throw new IllegalStateException("BeanFactory not initialized or already closed - " + "call 'refresh' before accessing beans via the ApplicationContext");   }   return beanFactory;}

if (beanFactory == null) 由于前面定义了 beanFactory，这里直接返回。

1 AbstractApplicationContext

1-1 获取 Bean

getBean(requiredType)

3 DefaultListableBeanFactory

public 
    
      T getBean(Class
     
       requiredType) throws BeansException {   // 获取 Bean   return getBean(requiredType, (Object[]) null);}
     
    

public 
    
      T getBean(Class
     
       requiredType, @Nullable Object... args) throws BeansException {   Assert.notNull(requiredType, "Required type must not be null");   // 解析 Bean   Object resolved = resolveBean(ResolvableType.forRawClass(requiredType), args, false);   if (resolved == null) {      throw new NoSuchBeanDefinitionException(requiredType);   }   return (T) resolved;}
     
    

3-1 解析 Bean

resolveBean(ResolvableType.forRawClass(requiredType), args, false)

private 
    
      T resolveBean(ResolvableType requiredType, @Nullable Object[] args, boolean nonUniqueAsNull) {    // 解析 Bean 命名    NamedBeanHolder
     
       namedBean = resolveNamedBean(requiredType, args, nonUniqueAsNull);    if (namedBean != null) {        return namedBean.getBeanInstance();    }    // 获取父级 Bean 工厂    BeanFactory parent = getParentBeanFactory();    if (parent instanceof DefaultListableBeanFactory) {        // 解析 Bean，递归调用        return ((DefaultListableBeanFactory) parent).resolveBean(requiredType, args, nonUniqueAsNull);    }    else if (parent != null) {        ObjectProvider
      
        parentProvider = parent.getBeanProvider(requiredType);        if (args != null) {            return parentProvider.getObject(args);        }        else {            return (nonUniqueAsNull ? parentProvider.getIfUnique() : parentProvider.getIfAvailable());        }    }    return null;}
      
     
    

3-2 解析 Bean 命名

resolveNamedBean(requiredType, args, nonUniqueAsNull)

private 
    
      NamedBeanHolder
     
       resolveNamedBean(ResolvableType requiredType, @Nullable Object[] args, boolean nonUniqueAsNull) throws BeansException {   Assert.notNull(requiredType, "Required type must not be null");   // 获取类型的 Bean 名称   String[] candidateNames = getBeanNamesForType(requiredType);   if (candidateNames.length > 1) {      List
      
        autowireCandidates = new ArrayList<>(candidateNames.length);      for (String beanName : candidateNames) {         if (!containsBeanDefinition(beanName) || getBeanDefinition(beanName).isAutowireCandidate()) {            autowireCandidates.add(beanName);         }      }      if (!autowireCandidates.isEmpty()) {         candidateNames = StringUtils.toStringArray(autowireCandidates);      }   }   if (candidateNames.length == 1) {      // 解析 Bean 命名      return resolveNamedBean(candidateNames[0], requiredType, args);   } else if (candidateNames.length > 1) {      Map
       
         candidates = CollectionUtils.newLinkedHashMap(candidateNames.length);      for (String beanName : candidateNames) {         if (containsSingleton(beanName) && args == null) {            Object beanInstance = getBean(beanName);            candidates.put(beanName, (beanInstance instanceof NullBean ? null : beanInstance));         } else {            candidates.put(beanName, getType(beanName));         }      }      // 确定主要候选      String candidateName = determinePrimaryCandidate(candidates, requiredType.toClass());      if (candidateName == null) {         // 确定最高优先级候选         candidateName = determineHighestPriorityCandidate(candidates, requiredType.toClass());      }      if (candidateName != null) {         Object beanInstance = candidates.get(candidateName);         if (beanInstance == null) {            return null;         }         if (beanInstance instanceof Class) {            // 解析 Bean 命名            return resolveNamedBean(candidateName, requiredType, args);         }         return new NamedBeanHolder<>(candidateName, (T) beanInstance);      }      if (!nonUniqueAsNull) {         throw new NoUniqueBeanDefinitionException(requiredType, candidates.keySet());      }   }   return null;}
       
      
     
    

3-3 确定主要候选

determinePrimaryCandidate(candidates, requiredType.toClass())

protected String determinePrimaryCandidate(Map
    
      candidates, Class
      requiredType) {   String primaryBeanName = null;   for (Map.Entry
     
       entry : candidates.entrySet()) {      String candidateBeanName = entry.getKey();      Object beanInstance = entry.getValue();      if (isPrimary(candidateBeanName, beanInstance)) {         if (primaryBeanName != null) {            boolean candidateLocal = containsBeanDefinition(candidateBeanName);            boolean primaryLocal = containsBeanDefinition(primaryBeanName);            if (candidateLocal && primaryLocal) {               throw new NoUniqueBeanDefinitionException(requiredType, candidates.size(), "more than one 'primary' bean found among candidates: " + candidates.keySet());            } else if (candidateLocal) {               primaryBeanName = candidateBeanName;            }         } else {            primaryBeanName = candidateBeanName;         }      }   }   return primaryBeanName;}
     
    

3-3 确定最高优先级候选

determineHighestPriorityCandidate(candidates, requiredType.toClass())

protected String determineHighestPriorityCandidate(Map
    
      candidates, Class
      requiredType) {   String highestPriorityBeanName = null;   Integer highestPriority = null;   for (Map.Entry
     
       entry : candidates.entrySet()) {      String candidateBeanName = entry.getKey();      Object beanInstance = entry.getValue();      if (beanInstance != null) {         Integer candidatePriority = getPriority(beanInstance);         if (candidatePriority != null) {            if (highestPriorityBeanName != null) {               if (candidatePriority.equals(highestPriority)) {                  throw new NoUniqueBeanDefinitionException(requiredType, candidates.size(), "Multiple beans found with the same priority ('" + highestPriority + "') among candidates: " + candidates.keySet());               } else if (candidatePriority < highestPriority) {                  highestPriorityBeanName = candidateBeanName;                  highestPriority = candidatePriority;               }            } else {               highestPriorityBeanName = candidateBeanName;               highestPriority = candidatePriority;            }         }      }   }   return highestPriorityBeanName;}