web.xml的url映射的小知识:
<url-pattern>/</url-pattern> 会匹配到/login这样的路径型url，不会匹配到模式为*.jsp这样的后缀型url
<url-pattern>/*</url-pattern> 会匹配所有url：路径型的和后缀型的url(包括/login,*.jsp,*.js和*.html等)
案例：
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
id="WebApp_ID" version="3.0">
<display-name>Task</display-name>
<!-- <context-param>
<param-name>webAppRootKey</param-name>
<param-value>Task.root</param-value>
</context-param> -->
<!-- spring配置 -->
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:spring.xml</param-value>
</context-param>
<!-- 加载spring配置文件：启动spring -->
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
</web-app>