spring源码分析之IOC（四）

接上篇
上篇说到BeanDefinitionReaderUtils将创建的BeanDefinitionHolder注册。这篇接着往下看。BeanDefinitionReaderUtils的registerBeanDefinition(bdHolder, getReaderContext().getRegistry());

/**
     * Register the given bean definition with the given bean factory.
     * @param definitionHolder the bean definition including name and aliases
     * @param registry the bean factory to register with
     * @throws BeanDefinitionStoreException if registration failed
     */
    public static void registerBeanDefinition(BeanDefinitionHolder definitionHolder,  BeanDefinitionRegistry registry) throws BeanDefinitionStoreException {

        // Register bean definition under primary name.
        String beanName = definitionHolder.getBeanName();
        registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());

        // Register aliases for bean name, if any.
        String[] aliases = definitionHolder.getAliases();
        if (aliases != null) {
            for (String alias : aliases) {
                registry.registerAlias(beanName, alias);
            }
        }
    }

在这个工具类中，BeanDefinitionHolder得到beanName和aliases，通过传入的registry通过beanName将当前bean注册，并且将当前bean的aliases(别名)注册。 这里关键只看注册bean的registerBeanDefinition()方法。继续走发现最终进入的就是DefaultListableBeanFactory这个实现类。

    //---------------------------------------------------------------------
    // Implementation of BeanDefinitionRegistry interface
    //---------------------------------------------------------------------

    @Override
    public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
            throws BeanDefinitionStoreException {

        Assert.hasText(beanName, "Bean name must not be empty");
        Assert.notNull(beanDefinition, "BeanDefinition must not be null");

        if (beanDefinition instanceof AbstractBeanDefinition) {
            try {
                ((AbstractBeanDefinition) beanDefinition).validate();
            }
            catch (BeanDefinitionValidationException ex) {
                throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
                        "Validation of bean definition failed", ex);
            }
        }

        BeanDefinition oldBeanDefinition;

        oldBeanDefinition = this.beanDefinitionMap.get(beanName);
        if (oldBeanDefinition != null) {
            if (!isAllowBeanDefinitionOverriding()) {
                throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
                        "Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
                        "': There is already [" + oldBeanDefinition + "] bound.");
            }
            else if (oldBeanDefinition.getRole() < beanDefinition.getRole()) {
                // e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
                if (this.logger.isWarnEnabled()) {
                    this.logger.warn("Overriding user-defined bean definition for bean '" + beanName +
                            "' with a framework-generated bean definition: replacing [" +
                            oldBeanDefinition + "] with [" + beanDefinition + "]");
                }
            }
            else if (!beanDefinition.equals(oldBeanDefinition)) {
                if (this.logger.isInfoEnabled()) {
                    this.logger.info("Overriding bean definition for bean '" + beanName +
                            "' with a different definition: replacing [" + oldBeanDefinition +
                            "] with [" + beanDefinition + "]");
                }
            }
            else {
                if (this.logger.isDebugEnabled()) {
                    this.logger.debug("Overriding bean definition for bean '" + beanName +
                            "' with an equivalent definition: replacing [" + oldBeanDefinition +
                            "] with [" + beanDefinition + "]");
                }
            }
            this.beanDefinitionMap.put(beanName, beanDefinition);
        }
        else {
            if (hasBeanCreationStarted()) {
                // Cannot modify startup-time collection elements anymore (for stable iteration)
                synchronized (this.beanDefinitionMap) {
                    this.beanDefinitionMap.put(beanName, beanDefinition);
                    List<String> updatedDefinitions = new ArrayList<String>(this.beanDefinitionNames.size() + 1);
                    updatedDefinitions.addAll(this.beanDefinitionNames);
                    updatedDefinitions.add(beanName);
                    this.beanDefinitionNames = updatedDefinitions;
                    if (this.manualSingletonNames.contains(beanName)) {
                        Set<String> updatedSingletons = new LinkedHashSet<String>(this.manualSingletonNames);
                        updatedSingletons.remove(beanName);
                        this.manualSingletonNames = updatedSingletons;
                    }
                }
            }
            else {
                // Still in startup registration phase
                this.beanDefinitionMap.put(beanName, beanDefinition);
                this.beanDefinitionNames.add(beanName);
                this.manualSingletonNames.remove(beanName);
            }
            this.frozenBeanDefinitionNames = null;
        }

        if (oldBeanDefinition != null || containsSingleton(beanName)) {
            resetBeanDefinition(beanName);
        }
    }

这段代码前面一大段都是针对如果当前bean经存在了所做的处理。else里面最关键的两行代码就是

    this.beanDefinitionNames.add(beanName);
    this.beanDefinitionMap.put(beanName, beanDefinition);

其中 this.beanDefinitionNames.add(beanName);这行代码是将beanName加入beanDefinitionNames这个List中。
this.beanDefinitionMap.put(beanName, beanDefinition);这行则是将beanName 和beanDefinition作为key-value放入beanDefinitionMap这个ConcurrentHashMap中。
至此。bean的解析和注册告一段落。Spring IOC容器的实例化大致如下图所示，IOC实例化的时候Bean的解析和注册也同时发生了。

**总结一下：
      XmlBeanDefinitionReader负责统计bean的注册个数和解析xml文档
      BeanDefinitionDocumentReader负责依据xml文档解析和注册bean
      BeanDefinitionParseDelegate负责实际的解析工作**

接下来则是继续按照AbstractApplicationContext的refresh()的执行顺序继续分析