- 研究IOC首先创建一个简单的web项目，在web.xml中我们都会加上这么一句
<context-param> <param-name>contextConfigLocation</param-name> <param-value>classpath:applicationContext.xml</param-value> </context-param> <listener> <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class> </listener>
这代表了web容器启动的时候会首先进入ContextLoaderListener这个类，并且之后会去加载classpath下的applicationContext.xml文件。那么重点就在ContextLoaderListener上，点开源码：
/** * Initialize the root web application context. */ @Override public void contextInitialized(ServletContextEvent event) { initWebApplicationContext(event.getServletContext()); } /** * Close the root web application context. */ @Override public void contextDestroyed(ServletContextEvent event) { closeWebApplicationContext(event.getServletContext()); ContextCleanupListener.cleanupAttributes(event.getServletContext()); }
里面主要为ServletContextListener接口的两个实现方法。web容器会首先调用contextInitialized方法，传入tomcat封装的容器资源，之后调用父类的初始化容器方法。
/** * The root WebApplicationContext instance that this loader manages. */ private WebApplicationContext context; public WebApplicationContext initWebApplicationContext(ServletContext servletContext) { ...........省略// Store context in local instance variable, to guarantee that // it is available on ServletContext shutdown. if (this.context == null) { this.context = createWebApplicationContext(servletContext); } if (this.context instanceof ConfigurableWebApplicationContext) { ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context; if (!cwac.isActive()) { // The context has not yet been refreshed -> provide services such as // setting the parent context, setting the application context id, etc if (cwac.getParent() == null) { // The context instance was injected without an explicit parent -> // determine parent for root web application context, if any. ApplicationContext parent = loadParentContext(servletContext); cwac.setParent(parent); } configureAndRefreshWebApplicationContext(cwac, servletContext); } } servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context); ClassLoader ccl = Thread.currentThread().getContextClassLoader(); if (ccl == ContextLoader.class.getClassLoader()) { currentContext = this.context; } else if (ccl != null) { currentContextPerThread.put(ccl, this.context); } ......省略 return this.context; }
这个方法里主要步骤createWebApplicationContext方法用来创建XmlWebApplicationContext这个root根容器，这个容器就是取自servletContextEvent。
loadParentContext方法用来加载父容器。主要方法configureAndRefreshWebApplicationContext用来配置和刷新root容器，在方法内最主要的就是refresh方法，里面实现了最主要的功能。
@Override public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { // Prepare this context for refreshing. prepareRefresh(); // Tell the subclass to refresh the internal bean factory. ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); // Prepare the bean factory for use in this context. prepareBeanFactory(beanFactory); try { // Allows post-processing of the bean factory in context subclasses. postProcessBeanFactory(beanFactory); // Invoke factory processors registered as beans in the context. invokeBeanFactoryPostProcessors(beanFactory); // Register bean processors that intercept bean creation. registerBeanPostProcessors(beanFactory); // Initialize message source for this context. initMessageSource(); // Initialize event multicaster for this context. initApplicationEventMulticaster(); // Initialize other special beans in specific context subclasses. onRefresh(); // Check for listener beans and register them. registerListeners(); // Instantiate all remaining (non-lazy-init) singletons. finishBeanFactoryInitialization(beanFactory); // Last step: publish corresponding event. 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; } } }
prepareRefresh方法用来准备之后需要用到的环境。
obtainFreshBeanFactory方法获取beanFactory
@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); } }
实际返回的beanFactory为其实现类DefaultListableBeanFactory，实例化该类用来为之后装载xml中实例化的类。
loadBeanDefinitions为重要的方法，用来真正的加载类了，之前的都是准备工作。
@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(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); }
在XmlWebApplicationContext中覆写此方法，内部创建了XmlBeanDefinitionReader类，用来作为xml中bean的读操作器，初始化环境后加载此类
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws IOException { String[] configLocations = getConfigLocations(); if (configLocations != null) { for (String configLocation : configLocations) { reader.loadBeanDefinitions(configLocation); } } }
之后获得之前初始化时放入数组的配置文件信息（比如：classpath:applicationContext.xml），用XmlBeanDefinitionReader加载此配置文件。
之后对xml文件信息进行编解码操作：
/** * Load bean definitions from the specified XML file. * @param resource the resource descriptor for the XML file * @return the number of bean definitions found * @throws BeanDefinitionStoreException in case of loading or parsing errors */ @Override public int loadBeanDefinitions(Resource resource) throws BeanDefinitionStoreException { return loadBeanDefinitions(new EncodedResource(resource)); }
关键步骤：
InputStream inputStream = encodedResource.getResource().getInputStream(); try { InputSource inputSource = new InputSource(inputStream); if (encodedResource.getEncoding() != null) { inputSource.setEncoding(encodedResource.getEncoding()); } return doLoadBeanDefinitions(inputSource, encodedResource.getResource()); } finally { inputStream.close(); }
之后正式加载获取到的xml资源解析
protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource) throws BeanDefinitionStoreException { Document doc = doLoadDocument(inputSource, resource); return registerBeanDefinitions(doc, resource); }
主要步骤是用sax对xml文件解析成Document元素，再注册进beanDefinitions容器中。
doLoadDocument方法的处理方法和sax对xml文档的处理方式就差不多了，具体可以参考sax解析xml流程
解析的过程很多，比如
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) { if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {//解析import importBeanDefinitionResource(ele); } else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {//解析alias processAliasRegistration(ele); } else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {//解析bean processBeanDefinition(ele, delegate); } else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {//解析beans // recurse doRegisterBeanDefinitions(ele); } }
将各个标签解析后注入容器。