BeanDefinition 合并

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：

  1  AnnotationConfigApplicationContext applicationContext
  2               = new AnnotationConfigApplicationContext(springConfiguration.class);
  3       //父 RootBeanDefinition        
  4       RootBeanDefinition rootBeanDefinition = new RootBeanDefinition();
  5       rootBeanDefinition.setScope(AbstractBeanDefinition.SCOPE_DEFAULT);
  6       rootBeanDefinition.getPropertyValues().add("name","xiaoming");
  7       applicationContext.registerBeanDefinition("parent",rootBeanDefinition);
  8   
  9   //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
  10   //那么合并过程中就会使用子类的
  11       ChildBeanDefinition childBeanDefinition = new ChildBeanDefinition("parent");
  12       childBeanDefinition.setBeanClass(A.class);
  13       childBeanDefinition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_NAME);
  14      
  15复制代码
  

  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 //...... } 复制代码

• DefaultListableBeanFactory#doGetBeanNamesForType

  private String[] doGetBeanNamesForType(ResolvableType type, boolean includeNonSingletons, boolean allowEagerInit) { List<String> result = new ArrayList<>();

  1    // 遍历所有的 beanDefinitionNames
  2    for (String beanName : this.beanDefinitionNames) {
  3        // Only consider bean as eligible if the bean name
  4        // is not defined as alias for some other bean.
  5        if (!isAlias(beanName)) {
  6            try {
  7            //获取合并的bd
  8                RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
  9            //.....
  10}
  

  复制代码

• AbstractBeanFactory#getMergedLocalBeanDefinition

  1protected RootBeanDefinition getMergedLocalBeanDefinition(String beanName) throws BeansException {
  2    // 先尝试从缓存获取bd（就是一个map）
  3    RootBeanDefinition mbd = this.mergedBeanDefinitions.get(beanName);
  4    if (mbd != null) {
  5        return mbd;
  6    }
  7    //合并bd
  8    return getMergedBeanDefinition(beanName, getBeanDefinition(beanName));
  9}
  

  复制代码

• AbstractBeanFactory#getMergedBeanDefinition

  1protected RootBeanDefinition getMergedBeanDefinition(
  2        String beanName, BeanDefinition bd, @Nullable BeanDefinition containingBd)
  3        throws BeanDefinitionStoreException {
  4
  5    synchronized (this.mergedBeanDefinitions) {
  6        RootBeanDefinition mbd = null;
  7
  8        // 先从缓存拿合并的bd
  9        if (containingBd == null) {
  10            mbd = this.mergedBeanDefinitions.get(beanName);
  11        }
  12          //合并的bd为空就进行bd合并
  13        if (mbd == null) {
  14           //如果父类为空，就不进行bd合并
  15            if (bd.getParentName() == null) {
  16                // Use copy of given root bean definition.
  17                if (bd instanceof RootBeanDefinition) {
  18                    mbd = ((RootBeanDefinition) bd).cloneBeanDefinition();
  19                }
  20                else {
  21                    mbd = new RootBeanDefinition(bd);
  22                }
  23            }
  24            else {
  25                // 进行bd合并
  26                BeanDefinition pbd;
  27                try {
  28                    String parentBeanName = transformedBeanName(bd.getParentName());
  29                    if (!beanName.equals(parentBeanName)) {
  30                       //父类的bd可能也需要合并，所以调用 getMergedBeanDefinition
  31                        pbd = getMergedBeanDefinition(parentBeanName);
  32                    }
  33                    else {
  34                        BeanFactory parent = getParentBeanFactory();
  35                        if (parent instanceof ConfigurableBeanFactory) {
  36                            pbd = ((ConfigurableBeanFactory) parent).getMergedBeanDefinition(parentBeanName);
  37                        }                       
  38                    }
  39                }
  40                //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
  41                mbd = new RootBeanDefinition(pbd);
  42                mbd.overrideFrom(bd);
  43            }
  44
  45            // Set default singleton scope, if not configured before.
  46            if (!StringUtils.hasLength(mbd.getScope())) {
  47                mbd.setScope(RootBeanDefinition.SCOPE_SINGLETON);
  48            }
  49        }
  50
  51        return mbd;
  52    }
  53}
  54
  55复制代码