apache-shiro杂记(三) 用了apache-shiro后，HttpSession.getServletContext() API无法正常工作了

用了apache-shiro以后，偶然发现servlet环境下(我开发时用的servlet3.0) HttpSession.getServletContext() 一直返回的是null 
查看了ShiroHttpSession实现类的源代码，结合shiro官方文档。发现修改web.xml可以解决这个问题。 

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
	version="3.0">

	<!-- apache-shiro 核心拦截器 -->
	<filter>
		<filter-name>shiroFilter</filter-name>
		<filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
		<init-param>
			<param-name>targetFilterLifecycle</param-name>
			<param-value>true</param-value>
		</init-param>
	</filter>
	<filter-mapping>
		<filter-name>shiroFilter</filter-name>
		<url-pattern>/*</url-pattern>
	</filter-mapping>
</web-app>