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");
  }
 }
});