<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>

public class ContextLoaderListener extends ContextLoader implements ServletContextListener {

    public ContextLoaderListener() {

    }

    public ContextLoaderListener(WebApplicationContext context) {

        super(context);

    }

    @Override

    public void contextInitialized(ServletContextEvent event) {

        initWebApplicationContext(event.getServletContext());

    }

    @Override

    public void contextDestroyed(ServletContextEvent event) {

        closeWebApplicationContext(event.getServletContext());

        ContextCleanupListener.cleanupAttributes(event.getServletContext());

    }

}

public interface ServletContextListener extends EventListener {

    /**

     * Receives notification that the web application initialization

     * process is starting.

     *

     * <p>All ServletContextListeners are notified of context

     * initialization before any filters or servlets in the web

     * application are initialized.

     *

     * @param sce the ServletContextEvent containing the ServletContext

     * that is being initialized

     */

    public void contextInitialized(ServletContextEvent sce);

    /**

     * Receives notification that the ServletContext is about to be

     * shut down.

     *

     * <p>All servlets and filters will have been destroyed before any

     * ServletContextListeners are notified of context

     * destruction.

     *

     * @param sce the ServletContextEvent containing the ServletContext

     * that is being destroyed

     */

    public void contextDestroyed(ServletContextEvent sce);

}

/**

     * Initialize Spring's web application context for the given servlet context,

     * using the application context provided at construction time, or creating a new one

     * according to the "{@link #CONTEXT_CLASS_PARAM contextClass}" and

     * "{@link #CONFIG_LOCATION_PARAM contextConfigLocation}" context-params.

     * @param servletContext current servlet context

     * @return the new WebApplicationContext

     * @see #ContextLoader(WebApplicationContext)

     * @see #CONTEXT_CLASS_PARAM

     * @see #CONFIG_LOCATION_PARAM

     */

    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) {

                //创建容器

                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);

                    }

                    //如果容器无效，则重置contextId，且重新加载contextConfigLocation配置

                    configureAndRefreshWebApplicationContext(cwac, servletContext);

                }

            }

            servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);

            //线程绑定容器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;

        }

    }