Spring中ContextLoaderListener监听详解

<listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
 
<context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>classpath:Resource/SpringConf.xml</param-value>
</context-param>
  
  
<servlet>
    <servlet-name>springweb</servlet-name>
    <servlet-class>
        org.springframework.web.servlet.DispatcherServlet
    </servlet-class>
	<init-param>  
		<param-name>contextConfigLocation</param-name>  
		<param-value>/WEB-INF/springweb.xml</param-value>  
	</init-param>  
    <load-on-startup>1</load-on-startup>
</servlet>
 
<servlet-mapping>
    <servlet-name>springweb</servlet-name>
    <url-pattern>/</url-pattern>
</servlet-mapping>

@Override
public void contextInitialized(ServletContextEvent event) {
    initWebApplicationContext(event.getServletContext());
}

public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
    // 省略部分日志和try catch代码
    long startTime = System.currentTimeMillis();
    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);
    }
    return this.context;
}

protected WebApplicationContext createWebApplicationContext(ServletContext sc) {
    Class<?> contextClass = determineContextClass(sc);
    if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
        throw new ApplicationContextException("省略");
    }
    return (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
}

protected Class<?> determineContextClass(ServletContext servletContext) {
    String contextClassName = servletContext.getInitParameter(CONTEXT_CLASS_PARAM);
    if (contextClassName != null) {
        // 省略try catch代码
        return ClassUtils.forName(contextClassName, ClassUtils.getDefaultClassLoader());
    }
    else {
        contextClassName = defaultStrategies.getProperty(WebApplicationContext.class.getName());
        // 省略try catch代码
        return ClassUtils.forName(contextClassName, ContextLoader.class.getClassLoader());
    }
}

org.springframework.web.context.WebApplicationContext=org.springframework.web.context.support.XmlWebApplicationContext

protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, 
                                                        ServletContext sc) {
    // 设置ConfigurableWebApplicationContext的容器Id
    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...
            wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
                    ObjectUtils.getDisplayString(sc.getContextPath()));
        }
    }
    // 设置Web容器上下文，设置到Spring容器中
    wac.setServletContext(sc);
    String configLocationParam = sc.getInitParameter(CONFIG_LOCATION_PARAM);
    // 配置location，如果配置的话，则refresh方法时会调用Resource加载，解析，初始化
    if (configLocationParam != null) {
        wac.setConfigLocation(configLocationParam);
    }
    // 设置Environment，refresh时也分析过，如果没有则会从java.lang.System中
    // 获取数据初始化StandardEnvironment或其子类
    ConfigurableEnvironment env = wac.getEnvironment();
    if (env instanceof ConfigurableWebEnvironment) {
        ((ConfigurableWebEnvironment) env).initPropertySources(sc, null);
    }
    // 初始化自定义的容器，如果自己配置的话（我们可以自定义实现ServletContextListener）
    customizeContext(sc, wac);
    // 调用refresh方法
    wac.refresh();
}