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

public class ContextLoaderListener extends ContextLoader implements ServletContextListener {

//由于他继承自ContextLoader，加载的时候当然会先加载他啦，那我们来看看这个类

}

private static final String DEFAULT_STRATEGIES_PATH = "ContextLoader.properties";//这个文件是在org.springframework.web.context.ContextLoader.properties他里面是

org.springframework.web.context.WebApplicationContext=org.springframework.web.context.support.XmlWebApplicationContext //这个后面再研究 以后就会把spring所有重要的东西都能看到了。    private static final Properties defaultStrategies;    static {        // Load default strategy implementations from properties file.        // This is currently strictly internal and not meant to be customized        // by application developers.        try {            ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, ContextLoader.class);            defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);//根据上面的properties文件，就能得到一个默认的properties了。        }        catch (IOException ex) {            throw new IllegalStateException("Could not load ‘ContextLoader.properties‘: " + ex.getMessage());        }    }

public void contextInitialized(ServletContextEvent event) {        this.contextLoader = createContextLoader();        if (this.contextLoader == null) {            this.contextLoader = this;        }        this.contextLoader.initWebApplicationContext(event.getServletContext());    }

    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);            }            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);            }            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;        }    }