使用Spring security如何防止用户的重复登录呢？如果用户账号已登录，这时再进行第二次或多次登录，需要阻止这样的多次登录。

一.在web.xml中配置listener

1. <context-param>  
2.         <param-name>contextConfigLocation</param-name>  
3.         <param-value>  
4.             classpath:/config/*.xml   
5.         </param-value>  
6.     </context-param>  
7.     <!-- spring监听 -->  
8.     <listener>  
9.         <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>  
10.     </listener>  
11.     <!-- Spring Security会话控制 -->  
12.     <listener>  
13.         <listener-class>org.springframework.security.web.session.HttpSessionEventPublisher</listener-class>  
14.     </listener>  
15. <!-- Spring security Filter -->  
16.     <filter>  
17.         <filter-name>springSecurityFilterChain</filter-name>  
18.         <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>  
19.     </filter>  
20.     <filter-mapping>  
21.         <filter-name>springSecurityFilterChain</filter-name>  
22.         <url-pattern>/*</url-pattern>  
23.     </filter-mapping>