BeanDefinition 的合并

• 1.BeanDefinition 有父子关系，有个属性叫parentName,通过parentName可以设置BeanDefinition的父子关系
• 2.为什么要设置BeanDefinition的父子关系，因为子类可以继承父类的属性，抽出共性，跟java的继承有点像
• 3.BeanDefinition 的合并过程就是将父子关系的 BeanDefinition 属性合并起来，如果有相同的就使用子类的属性值 例子：

  
      
  
       
  
        
  
         
  
        
        
  
         
  
            AnnotationConfigApplicationContext applicationContext
         
        
       
  
        
  
         
  
        
        
  
         
  
           = new AnnotationConfigApplicationContext(springConfiguration.class);
         
        
       
  
        
  
         
  
        
        
  
         
  
           //父 RootBeanDefinition 
         
        
       
  
        
  
         
  
        
        
  
         
  
           RootBeanDefinition rootBeanDefinition = new RootBeanDefinition();
         
        
       
  
        
  
         
  
        
        
  
         
  
           rootBeanDefinition.setScope(AbstractBeanDefinition.SCOPE_DEFAULT);
         
        
       
  
        
  
         
  
        
        
  
         
  
           rootBeanDefinition.getPropertyValues().add("name","xiaoming");
         
        
       
  
        
  
         
  
        
        
  
         
  
           applicationContext.registerBeanDefinition("parent",rootBeanDefinition);
         
        
       
  
        
  
         
  
        
        
  
         
     
         
        
       
  
        
  
         
  
        
        
  
         
     //子 ChildBeanDefinition ，会继承使用父类已有的属性值，但是如果属性值冲突，不一样
         
        
       
  
        
  
         
  
        
        
  
         
     //那么合并过程中就会使用子类的
         
        
       
  
        
  
         
  
        
        
  
         
  
           ChildBeanDefinition childBeanDefinition = new ChildBeanDefinition("parent");
         
        
       
  
        
  
         
  
        
        
  
         
  
           childBeanDefinition.setBeanClass(A.class);
         
        
       
  
        
  
         
  
        
        
  
         
  
           childBeanDefinition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_NAME);
         
        
       
  
        
  
         
  
        
        
  
         
   
         
        
       
  
        
  
         
  
        
        
  
         
  
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  什么时候做合并

  在初始化bean工厂的过程中调用： PostProcessorRegistrationDelegate#invokeBeanFactoryPostProcessors->DefaultListableBeanFactory.getBeanNamesForType
• DefaultListableBeanFactory.getBeanNamesForType

  

   

    

     

    
    

     

      public String[] getBeanNamesForType(@Nullable Class<?> type, boolean includeNonSingletons, boolean allowEagerInit) {
     
    
   

    

     

    
    

     
 //....... 
     
    
   

    

     

    
    

     
 return doGetBeanNamesForType
     
    
   

    

     

    
    

     
 //......
     
    
   

    

     

    
    

     

       }
     
    
   

    

     

    
    

     

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• DefaultListableBeanFactory#doGetBeanNamesForType

  

   

    

     

    
    

     

      private String[] doGetBeanNamesForType(ResolvableType type, boolean includeNonSingletons, boolean allowEagerInit) {
     
    
   

    

     

    
    

     

       List<String> result = new ArrayList<>();
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
 // 遍历所有的 beanDefinitionNames
     
    
   

    

     

    
    

     
 for (String beanName : this.beanDefinitionNames) {
     
    
   

    

     

    
    

     
 // Only consider bean as eligible if the bean name
     
    
   

    

     

    
    

     
 // is not defined as alias for some other bean.
     
    
   

    

     

    
    

     
 if (!isAlias(beanName)) {
     
    
   

    

     

    
    

     
 try {
     
    
   

    

     

    
    

     
 //获取合并的bd
     
    
   

    

     

    
    

     

       RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
     
    
   

    

     

    
    

     
 //.....
     
    
   

    

     

    
    

     

       }
     
    
   

    

     

    
    

     

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• AbstractBeanFactory#getMergedLocalBeanDefinition

  

   

    

     

    
    

     
 
     
    
   

    

     

    
    

     
 protected RootBeanDefinition getMergedLocalBeanDefinition(String beanName) throws BeansException {
     
    
   

    

     

    
    

     
 // 先尝试从缓存获取bd（就是一个map）
     
    
   

    

     

    
    

     

       RootBeanDefinition mbd = this.mergedBeanDefinitions.get(beanName);
     
    
   

    

     

    
    

     
 if (mbd != null) {
     
    
   

    

     

    
    

     
 return mbd;
     
    
   

    

     

    
    

     

       }
     
    
   

    

     

    
    

     
 //合并bd
     
    
   

    

     

    
    

     
 return getMergedBeanDefinition(beanName, getBeanDefinition(beanName));
     
    
   

    

     

    
    

     

       }
     
    
   

    

     

    
    

     

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• AbstractBeanFactory#getMergedBeanDefinition

  
      
  
       
  
        
  
         
  
        
        
  
         
  
          protected RootBeanDefinition getMergedBeanDefinition(
         
        
       
  
        
  
         
  
        
        
  
         
  
           String beanName, BeanDefinition bd, @Nullable BeanDefinition containingBd)
         
        
       
  
        
  
         
  
        
        
  
         
   throws BeanDefinitionStoreException {
         
        
       
  
        
  
         
  
        
        
  
         
   
         
        
       
  
        
  
         
  
        
        
  
         
   synchronized (this.mergedBeanDefinitions) {
         
        
       
  
        
  
         
  
        
        
  
         
  
           RootBeanDefinition mbd = null;
         
        
       
  
        
  
         
  
        
        
  
         
   
         
        
       
  
        
  
         
  
        
        
  
         
   // 先从缓存拿合并的bd
         
        
       
  
        
  
         
  
        
        
  
         
   if (containingBd == null) {
         
        
       
  
        
  
         
  
        
        
  
         
  
           mbd = this.mergedBeanDefinitions.get(beanName);
         
        
       
  
        
  
         
  
        
        
  
         
  
           }
         
        
       
  
        
  
         
  
        
        
  
         
   //合并的bd为空就进行bd合并
         
        
       
  
        
  
         
  
        
        
  
         
   if (mbd == null) {
         
        
       
  
        
  
         
  
        
        
  
         
   //如果父类为空，就不进行bd合并
         
        
       
  
        
  
         
  
        
        
  
         
   if (bd.getParentName() == null) {
         
        
       
  
        
  
         
  
        
        
  
         
   // Use copy of given root bean definition.
         
        
       
  
        
  
         
  
        
        
  
         
   if (bd instanceof RootBeanDefinition) {
         
        
       
  
        
  
         
  
        
        
  
         
  
           mbd = ((RootBeanDefinition) bd).cloneBeanDefinition();
         
        
       
  
        
  
         
  
        
        
  
         
  
           }
         
        
       
  
        
  
         
  
        
        
  
         
   else {
         
        
       
  
        
  
         
  
        
        
  
         
  
           mbd = new RootBeanDefinition(bd);
         
        
       
  
        
  
         
  
        
        
  
         
  
           }
         
        
       
  
        
  
         
  
        
        
  
         
  
           }
         
        
       
  
        
  
         
  
        
        
  
         
   else {
         
        
       
  
        
  
         
  
        
        
  
         
   // 进行bd合并
         
        
       
  
        
  
         
  
        
        
  
         
  
           BeanDefinition pbd;
         
        
       
  
        
  
         
  
        
        
  
         
   try {
         
        
       
  
        
  
         
  
        
        
  
         
  
           String parentBeanName = transformedBeanName(bd.getParentName());
         
        
       
  
        
  
         
  
        
        
  
         
   if (!beanName.equals(parentBeanName)) {
         
        
       
  
        
  
         
  
        
        
  
         
   //父类的bd可能也需要合并，所以调用 getMergedBeanDefinition
         
        
       
  
        
  
         
  
        
        
  
         
  
           pbd = getMergedBeanDefinition(parentBeanName);
         
        
       
  
        
  
         
  
        
        
  
         
  
           }
         
        
       
  
        
  
         
  
        
        
  
         
   else {
         
        
       
  
        
  
         
  
        
        
  
         
  
           BeanFactory parent = getParentBeanFactory();
         
        
       
  
        
  
         
  
        
        
  
         
   if (parent instanceof ConfigurableBeanFactory) {
         
        
       
  
        
  
         
  
        
        
  
         
  
           pbd = ((ConfigurableBeanFactory) parent).getMergedBeanDefinition(parentBeanName);
         
        
       
  
        
  
         
  
        
        
  
         
  
           } 
         
        
       
  
        
  
         
  
        
        
  
         
  
           }
         
        
       
  
        
  
         
  
        
        
  
         
  
           }
         
        
       
  
        
  
         
  
        
        
  
         
   //进行bd合并，子类覆盖父类的，如果子类没有，就用父类的属性
         
        
       
  
        
  
         
  
        
        
  
         
  
           mbd = new RootBeanDefinition(pbd);
         
        
       
  
        
  
         
  
        
        
  
         
  
           mbd.overrideFrom(bd);
         
        
       
  
        
  
         
  
        
        
  
         
  
           }
         
        
       
  
        
  
         
  
        
        
  
         
   
         
        
       
  
        
  
         
  
        
        
  
         
   // Set default singleton scope, if not configured before.
         
        
       
  
        
  
         
  
        
        
  
         
   if (!StringUtils.hasLength(mbd.getScope())) {
         
        
       
  
        
  
         
  
        
        
  
         
  
           mbd.setScope(RootBeanDefinition.SCOPE_SINGLETON);
         
        
       
  
        
  
         
  
        
        
  
         
  
           }
         
        
       
  
        
  
         
  
        
        
  
         
  
           }
         
        
       
  
        
  
         
  
        
        
  
         
   
         
        
       
  
        
  
         
  
        
        
  
         
   return mbd;
         
        
       
  
        
  
         
  
        
        
  
         
  
           }
         
        
       
  
        
  
         
  
        
        
  
         
  
          }
         
        
       
  
        
  
         
  
        
        
  
         
   
         
        
       
  
        
  
         
  
        
        
  
         
  
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文章来源: javaedge.blog.csdn.net，作者：JavaEdge.，版权归原作者所有，如需转载，请联系作者。

原文链接：javaedge.blog.csdn.net/article/details/108177864