过滤器可以实现用户身份验证的功能，如果用户没有登录，则跳转到登陆页面：
本例实现：
过滤器类：
package com.start.util;
import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.util.List;
import java.util.ArrayList;
import java.util.StringTokenizer;
import java.io.IOException;
/**
* 用于检测用户是否登陆的过滤器，如果未登录，则重定向到指的登录页面
* 配置参数
* checkSessionKey 需检查的在 Session 中保存的关键字
* redirectURL 如果用户未登录，则重定向到指定的页面，URL不包括 ContextPath
* notCheckURLList 不做检查的URL列表，以分号分开，并且 URL 中不包括 ContextPath
*/
public class CheckLoginFilter implements Filter {
protected FilterConfig filterConfig = null;
private String redirectURL = null;
private List notCheckURLList = new ArrayList();
private String sessionKey = null;
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException
{
HttpServletRequest request = (HttpServletRequest) servletRequest;
HttpServletResponse response = (HttpServletResponse) servletResponse;
HttpSession session = request.getSession();
if(sessionKey == null)
{
filterChain.doFilter(request, response);
return;
}
if((!checkRequestURIIntNotFilterList(request)) && session.getAttribute(sessionKey) == null)
{
response.sendRedirect(request.getContextPath() + redirectURL);
return;
}
filterChain.doFilter(servletRequest, servletResponse);
}
public void destroy()
{
notCheckURLList.clear();
}
private boolean checkRequestURIIntNotFilterList(HttpServletRequest request)
{
String uri = request.getServletPath() + (request.getPathInfo() == null ? "" : request.getPathInfo());
return notCheckURLList.contains(uri);
}
public void init(FilterConfig filterConfig) throws ServletException
{
this.filterConfig = filterConfig;
redirectURL = filterConfig.getInitParameter("redirectURL");
sessionKey = filterConfig.getInitParameter("checkSessionKey");
String notCheckURLListStr = filterConfig.getInitParameter("notCheckURLList");
if(notCheckURLListStr != null)
{
StringTokenizer st = new StringTokenizer(notCheckURLListStr, ";");
notCheckURLList.clear();
while(st.hasMoreTokens())
{
notCheckURLList.add(st.nextToken());
}
}
}
}
直接复制过去就可以了，不用修改。
配置文件，也就是对过滤器的注册了，web.xml中：
<!-- servlet 过滤器 -->
<filter>
<filter-name>CheckLoginFilter</filter-name>
<filter-class>com.start.util.CheckLoginFilter</filter-class>
<init-param>
<param-name>checkSessionKey</param-name>
<param-value>forUser</param-value>
</init-param>
<init-param>
<param-name>redirectURL</param-name>
<param-value>/index.jsp</param-value>
</init-param>
<init-param>
<param-name>notCheckURLList </param-name>
<param-value>/error.jsp;/index.jsp;/m/file/login.action</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>CheckLoginFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
大的格式相信大家都明白，解释下变量：
checkSessionKey：web下的session本身就是一个map，checkSessionKey就是取map的key，即你set进去的表面用户身份的session的key。
redirectURL：看这段代码 if((!checkRequestURIIntNotFilterList(request)) && session.getAttribute(sessionKey) == null)
{
response.sendRedirect(request.getContextPath() + redirectURL);
return;
} 都明白了吧？就是如果没有登录用户，则跳转到的页面。
notCheckURLList ：这个就是不需要过滤的页面啦