自我分析-Spring IOC在Web应用的启动和销毁

Spring IOC容器通过ServletContextListener对servlet容器的生命周期监听，从而实现了IOC的启动和销毁。

注意：

1.分析框架代码时，要常使用类继承、调用关系等快捷键，可以更高效的学习，快捷键可以设置成你习惯的按键；

2.本文重在怎么自我分析框架代码，所以对其中解析需自己实际跟踪代码实践方可；

3.spring源代码版本 spring-framework-3.2.1.RELEASE。

预览

javax.servlet.ServletContext，Servlet容器接口。

javax.servlet.ServletContextListener，Servlet容器生命周期监听接口。

org.springframework.web.context.ContextLoaderListener，Spring IOC容器生命周期监听类。

org.springframework.web.context.ContextLoader，Spring
IOC容器启动和销毁。

配置-监听ServletContext生命周期

在web.xml中spring配置了对ServletContext生命周期的监听，当Web容器启动和销毁时，触发Spring定义的IOC容器的启动和销毁，具体配置如下：

<listener>
		<listener-class>
			org.springframework.web.context.ContextLoaderListener
		</listener-class>
	</listener>

入口-ContextLoaderListener对Spring IOC初始化和销毁

当web容器启动时会触发contextInitialized方法对spring ioc容器进行初始化，销毁时会触发contextDestroyed方法对spring ioc容器进行销毁，ServletContextListener接口如下：

    public void contextInitialized ( ServletContextEvent sce );  // ServletContext启动时触发

    public void contextDestroyed ( ServletContextEvent sce );    // ServletContext销毁时触发

Spring IOC启动

spring ioc容器初始化具体代码如下：

org.springframework.web.context.ContextLoaderListener

	public void contextInitialized(ServletContextEvent event) {
		this.contextLoader = createContextLoader();
		if (this.contextLoader == null) {
			this.contextLoader = this;
		}
		// 对spring ioc容器进行初始化
		this.contextLoader.initWebApplicationContext(event.getServletContext());
	}

IOC容器的初始化是由ContextLoader类执行：

org.springframework.web.context.ContextLoader

	public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
		// 是否已经加载IOC容器
		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);
			}
			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);
					}
					// 此方法是刷新初始化IOC容器的地方
					configureAndRefreshWebApplicationContext(cwac, servletContext);
				}
			}
			// IOC容器加载后，将IOC容器保存于ServletContext容器中
			servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);

		...
	}

熟悉的refresh()方法的调用：

org.springframework.web.context.ContextLoader  

	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);
			}
			else {
				// Generate default id...
				if (sc.getMajorVersion() == 2 && sc.getMinorVersion() < 5) {
					// Servlet <= 2.4: resort to name specified in web.xml, if any.
					wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
							ObjectUtils.getDisplayString(sc.getServletContextName()));
				}
				else {
					wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
							ObjectUtils.getDisplayString(sc.getContextPath()));
				}
			}
		}

		wac.setServletContext(sc);
		String initParameter = sc.getInitParameter(CONFIG_LOCATION_PARAM);
		if (initParameter != null) {
			wac.setConfigLocation(initParameter);
		}
		customizeContext(sc, wac);

		// 熟悉的refresh()对Spring IOC容器进行加载，接下来的步骤就是 "自我分析-Spring IOC"文脏中的内容
		wac.refresh();
	}

Spring IOC销毁

对Spring IOC容器和其他Spring环境信息进行销毁：

org.springframework.web.context.ContextLoaderListener

	public void contextDestroyed(ServletContextEvent event) {
		if (this.contextLoader != null) {
			this.contextLoader.closeWebApplicationContext(event.getServletContext());
		}
		ContextCleanupListener.cleanupAttributes(event.getServletContext());
	}

具体清理销毁了spring的什么东西，自己再跟踪下代码即可。

若文中存在分析错误，望留言指出，在此非常感谢。