Spring 使用简单Demo进行源码调试（三）

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版权声明：本文为博主原创文章，转载请注明出处：http://blog.jerkybible.com/2015/05/11/Spring 使用简单Demo进行源码调试（三）/

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接上篇日志Spring 使用简单Demo进行源码调试（二）继续。

上篇提到了主要的初始化函数refresh，函数源码如下：

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public void refresh() throws BeansException, IllegalStateException {
        synchronized (this.startupShutdownMonitor) {
            // 为了刷新准备上下文
            prepareRefresh();
            // 利用子类完成内部bean factory的刷新
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
            // 使用本地上下文准备bean factory
            prepareBeanFactory(beanFactory);
            try {
                // 允许在上下文子类中完成bean factory后处理
                postProcessBeanFactory(beanFactory);
                // 调用上下文注册的bean factory处理器
                invokeBeanFactoryPostProcessors(beanFactory);
                // 注册拦截bean创建的bean处理器
                registerBeanPostProcessors(beanFactory);
                // 初始化上下文中消息源
                initMessageSource();
                // 初始化上下文中的事件多播
                initApplicationEventMulticaster();
                // 在特定上下文子类中初始化其他特殊bean
                onRefresh();
                // 检查监听器bean并注册 
                registerListeners();
                // 实例化所有剩余(non-lazy-init)单例
                finishBeanFactoryInitialization(beanFactory);
                // 发布相应的事件
                finishRefresh();
            }
            catch (BeansException ex) {
                logger.warn("Exception encountered during context initialization - cancelling refresh attempt", ex);
                // Destroy already created singletons to avoid dangling resources.
                destroyBeans();
                // Reset 'active' flag.
                cancelRefresh(ex);
                // Propagate exception to caller.
                throw ex;
            }
        }
    }

先把prepareRefresh的代码贴出来。这段代码主要功能是初始化

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/**
	 * Prepare this context for refreshing, setting its startup date and
	 * active flag as well as performing any initialization of property sources.
	 */
	protected void prepareRefresh() {
		this.startupDate = System.currentTimeMillis();
		synchronized (this.activeMonitor) {
			this.active = true;
		}
		if (logger.isInfoEnabled()) {
			logger.info("Refreshing " + this);
		}
		// Initialize any placeholder property sources in the context environment
		initPropertySources();
		// Validate that all properties marked as required are resolvable
		// see ConfigurablePropertyResolver#setRequiredProperties
		getEnvironment().validateRequiredProperties();
	}

这块基本是数据准备功能， 目前这一块没有实际用到。
接着我们看比较重要的一步

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// 利用子类完成内部bean factory的刷新
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

先展开obtainFreshBeanFactory函数

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/**
	 * Tell the subclass to refresh the internal bean factory.
         * 使用子类完成内部bean factory
	 * @return the fresh BeanFactory instance
	 * @see #refreshBeanFactory()
	 * @see #getBeanFactory()
	 */
	protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
		refreshBeanFactory();
		ConfigurableListableBeanFactory beanFactory = getBeanFactory();
		if (logger.isDebugEnabled()) {
			logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
		}
		return beanFactory;
	}

我们主要看refreshBeanFactory()这一步,分为以下步骤：
1. 如果有bean factory，删除之；
2. 新建一个bean factory；
3. 设置一个序列化Id；
4. 使用的上下文自定义内部bean factory；
5. 加载bean 定义

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/**
	 * This implementation performs an actual refresh of this context's underlying
	 * bean factory, shutting down the previous bean factory (if any) and
	 * initializing a fresh bean factory for the next phase of the context's lifecycle.
	 */
	@Override
	protected final void refreshBeanFactory() throws BeansException {
		if (hasBeanFactory()) {
			destroyBeans();
			closeBeanFactory();
		}
		try {
			DefaultListableBeanFactory beanFactory = createBeanFactory();
			beanFactory.setSerializationId(getId());
			customizeBeanFactory(beanFactory);
			loadBeanDefinitions(beanFactory);
			synchronized (this.beanFactoryMonitor) {
				this.beanFactory = beanFactory;
			}
		}
		catch (IOException ex) {
			throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
		}
	}

现在看一下第5步，加载bean定义，其实现如下。可以看到，这一步将beanFactory传入XmlBeanDefinitionReader的构造函数，新建一个XmlBeanDefinitionReader对象，然后对其环境进行设置。其中Environment表示当前应用程序运行的环境接口；ResourceLoader表示加载资源策略接口；EntityResolver表示实体解析接口。最后初始化XmlBeanDefinitionReader对象，然后使用这个对象加载bean 定义。

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/**
	 * Loads the bean definitions via an XmlBeanDefinitionReader.
	 * @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader
	 * @see #initBeanDefinitionReader
	 * @see #loadBeanDefinitions
	 */
	@Override
	protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
		// Create a new XmlBeanDefinitionReader for the given BeanFactory.
		XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
		// Configure the bean definition reader with this context's
		// resource loading environment.
		beanDefinitionReader.setEnvironment(this.getEnvironment());
		beanDefinitionReader.setResourceLoader(this);
		beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
		// Allow a subclass to provide custom initialization of the reader,
		// then proceed with actually loading the bean definitions.
		initBeanDefinitionReader(beanDefinitionReader);
		loadBeanDefinitions(beanDefinitionReader);
	}

再看下一步，这个方法比较好理解，就是使用已有的配置资源或者配置文件进行加载，当前没有配置资源，所以只使用配置文件进行加载。

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/**
	 * 使用XmlBeanDefinitionReader实例加载bean定义
	 * @param reader the XmlBeanDefinitionReader to use
	 */
	protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
		Resource[] configResources = getConfigResources();
		if (configResources != null) {
			reader.loadBeanDefinitions(configResources);
		}
		String[] configLocations = getConfigLocations();
		if (configLocations != null) {
			reader.loadBeanDefinitions(configLocations);
		}
	}

来看reader.loadBeanDefinitions(configLocations);这一步。这一步看起来很复杂，但最主要的还是loadBeanDefinitions(resources)这一步。

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/**
	 * 使用配置文件加载bean定义	
	 */
	public int loadBeanDefinitions(String location, Set<Resource> actualResources) throws BeanDefinitionStoreException {
		ResourceLoader resourceLoader = getResourceLoader();
		if (resourceLoader == null) {
			throw new BeanDefinitionStoreException(
					"Cannot import bean definitions from location [" + location + "]: no ResourceLoader available");
		}
		if (resourceLoader instanceof ResourcePatternResolver) {
			// Resource pattern matching available.
			try {
				Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);
				int loadCount = loadBeanDefinitions(resources);
				if (actualResources != null) {
					for (Resource resource : resources) {
						actualResources.add(resource);
					}
				}
				if (logger.isDebugEnabled()) {
					logger.debug("Loaded " + loadCount + " bean definitions from location pattern [" + location + "]");
				}
				return loadCount;
			}
			catch (IOException ex) {
				throw new BeanDefinitionStoreException(
						"Could not resolve bean definition resource pattern [" + location + "]", ex);
			}
		}
		else {
			// Can only load single resources by absolute URL.
			Resource resource = resourceLoader.getResource(location);
			int loadCount = loadBeanDefinitions(resource);
			if (actualResources != null) {
				actualResources.add(resource);
			}
			if (logger.isDebugEnabled()) {
				logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");
			}
			return loadCount;
		}
	}

下一回展开loadBeanDefinitions(resources)。

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