转载：http://www.cnblogs.com/morlin/p/4928542.html

一般来说我们的项目都有登录过滤器，一般请求足以搞定。但是AJAX却是例外的，所以解决方法是设置响应为session失效。

一共分为过滤器和页面JS两个部分的设置，先看过滤器的修改：

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;


/**
 * 登录过滤器
 *　　拥有Session是否失效和用户是否登录2个条件判断
 *　　如果是ajax请求则设置session超时
 * @author Merlin.Ma
 *
 */
public class LoginFilter implements Filter{
    
    private String redirectUrl = "/login.html";
    private String sessionKey = "userName";

    @Override
    public void destroy() {
    }

    @Override
    public void doFilter(ServletRequest request,ServletResponse response,FilterChain chain) throws IOException,ServletException {
        
        HttpServletRequest req = (HttpServletRequest) request;
        HttpServletResponse rep = (HttpServletResponse) response;
        
        HttpSession session = req.getSession();
        
        if( session == null || session.getAttribute(sessionKey) == null){
            //如果判断是 AJAX 请求,直接设置为session超时
            if( req.getHeader("x-requested-with") != null && req.getHeader("x-requested-with").equals("XMLHttpRequest")  ) {
            
                rep.setHeader("sessionstatus","timeout"); 
                
            } else {
                rep.sendRedirect( req.getContextPath() + redirectUrl);
            }
            
        }else {
            chain.doFilter(request,response);
        }      
    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        
        String url = filterConfig.getInitParameter("redirectUrl");
        String key = filterConfig.getInitParameter("sessionKey");
        
        redirectUrl = url == null? redirectUrl:url;
        sessionKey = key == null ? sessionKey : key ;
    }  
}

//全局的ajax访问，处理ajax清求时sesion超时 
$.ajaxSetup({
    contentType : "application/x-www-form-urlencoded;charset=utf-8",complete : function(XMLHttpRequest,textStatus) {
        var sessionstatus = XMLHttpRequest.getResponseHeader("sessionstatus"); // 通过XMLHttpRequest取得响应头，sessionstatus，
        if (sessionstatus == "timeout") {
            // 如果超时就处理 ，指定要跳转的页面
            window.location.replace("login.html");
        }
    }
});