Spring源码解读——Spring容器初始化 1

如果你是Spring新手的话，可以去http://download.csdn.net/detail/chenxuegui123/6881245下一些源代码例子跟着调试运行

 

 因为WebApplicationContext 需要ServletContext 实例，也就是说它必须在拥有Web 容器的前提下才能完成启动的工作。有过Web 开发经验的读者都知道可以在web.xml 中配置自启动的Servlet 或定义Web 容器监听器（ServletContextListener），借助这两者中的任何一个，我们就可以完成启动Spring Web 应用上下文的工作。

    Spring 分别提供了用于启动WebApplicationContext 的Servlet 和Web 容器监听器：
   org.springframework.web.context.ContextLoaderServlet；
   org.springframework.web.context.ContextLoaderListener。
两者的内部都实现了启动WebApplicationContext 实例的逻辑，我们只要根据Web 容器的具体情况选择两者之一，并在web.xml 中完成配置就可以了。

以下以ContextLoaderListener为例子说明

ContextLoaderListener相关配置的注意事项看Spring笔记1——控制反转容器

那通过ContextLoaderListener，Spring是怎么怎么初始化和配置Spring容器（WebApplicationContext）的呢？

Spring容器的初始化过程：

接下来再详细从代码上介绍吧

ContextLoaderListener的体系结构

部署spring例子到tomcat，运行tomcat

这里开始了ContextLoaderListener的工作了，首先是Spring容器（这里是WebApplicationContext）的初始化

 ContextLoader       
       /**
	 * Initialize the root web application context.
	 */
	@Override
	public void contextInitialized(ServletContextEvent event) {
		initWebApplicationContext(event.getServletContext());
	}

再看一下ContextLoader的initWebApplicationContext()

ContextLoader
public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
		if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) {
			throw new IllegalStateException(
					"Cannot initialize context because there is already a root application context present - " +
					"check whether you have multiple ContextLoader* definitions in your web.xml!");
		}

		Log logger = LogFactory.getLog(ContextLoader.class);
		servletContext.log("Initializing Spring root WebApplicationContext");
		if (logger.isInfoEnabled()) {
			logger.info("Root WebApplicationContext: initialization started");
		}
		long startTime = System.currentTimeMillis();

		try {
			// Store context in local instance variable, to guarantee that
			// it is available on ServletContext shutdown.
			if (this.context == null) {
				this.context = createWebApplicationContext(servletContext);      //这里根据ServletContext创建Spring容器(在这里创建的是XmlWebApplicationContext)
			}
			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);  //这里进行WebApplicationContext的配置工作，其中包括把servletContext和Spring容器关联起来，以及将配置文件（applicationContext.xml）加入到容器中
				}
			}
			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);
			}

			if (logger.isDebugEnabled()) {
				logger.debug("Published root WebApplicationContext as ServletContext attribute with name [" +
						WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE + "]");
			}
			if (logger.isInfoEnabled()) {
				long elapsedTime = System.currentTimeMillis() - startTime;
				logger.info("Root WebApplicationContext: initialization completed in " + elapsedTime + " ms");
			}

			return this.context;
		}
		catch (RuntimeException ex) {
			logger.error("Context initialization failed", ex);
			servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex);
			throw ex;
		}
		catch (Error err) {
			logger.error("Context initialization failed", err);
			servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, err);
			throw err;
		}
	}

再进入createWebApplicationContext()

//ContextLoader
protected WebApplicationContext createWebApplicationContext(ServletContext sc) {
		Class contextClass = determineContextClass(sc); //返回WebApplicationContext实现类使用,默认XmlWebApplicationContext或如果指定一个自定义上下文类。
		if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
			throw new ApplicationContextException("Custom context class [" + contextClass.getName() +
					"] is not of type [" + ConfigurableWebApplicationContext.class.getName() + "]");
		}
		return (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
	}

再看determineConetxt()

可以看到在这里其实就是根据Parameter CONTEXT_CLASSPARAM去实例化一个WebApplicatoinContext，而该参数其实在web.xml已经配置为XmlWebApplicationContext(WebApplicationContext实现类) ,看web.xml

//web.xml

  
    contextClass
    
  	org.springframework.web.context.support.XmlWebApplicationContext
  	
  

接着，我们回到initWebApplicationContext（），其中调用的configureAndRefreshWebApplicationContext(cwac, servletContext);我们看一下他的实现

protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) {
		if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
			// The application context id is still set to its original default value
			// -> assign a more useful id based on available information
			String idParam = sc.getInitParameter(CONTEXT_ID_PARAM);    
			if (idParam != null) {
				wac.setId(idParam);    //这里设置WebApplicationContext的id值为contextId也就是我们浏览器访问的localhost:8080/01/中的01
			}
			else {
				// Generate default id...
				wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
						ObjectUtils.getDisplayString(sc.getContextPath()));
			}
		}

		wac.setServletContext(sc);
		String initParameter = sc.getInitParameter(CONFIG_LOCATION_PARAM);//这里设置Web.xml中配置的contextConfigLocation参数，也就是配置文件applicationContext.xml了
		if (initParameter != null) {
			wac.setConfigLocation(initParameter);
		}
		customizeContext(sc, wac);
		wac.refresh();   //加载刚才的配置文件applicationContext.xml,以及bean的实例化
	}

看一下web.xml中的contextConfigLocation设置吧

再看一下

//XmlWebApplicationContext
@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) {
				// Destroy already created singletons to avoid dangling resources.
				destroyBeans();

				// Reset 'active' flag.
				cancelRefresh(ex);

				// Propagate exception to caller.
				throw ex;
			}
		}
	}

这个方法就是配置Spirng Web容器，根据applicationContext.xml实例化类的重中之重了，东西太多了，下篇博客再接着说吧