如果是判断是否登录拦截器

package com.ccsu.common.filter;

import com.ccsu.common.constants.SessionConstants;
import com.ccsu.entity.userSystem.User;
import com.ccsu.util.userSystem.ProsReader;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.http.HttpStatus;
import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

/**
 * Created with IntelliJ IDEA.
 * User: Ambitor springMVC拦截器 判断session中用户是否过期
 * Date: 13-6-27
 * Time: 下午7:31
 * To change this template use File | Settings | File Templates.
 *
 * @author 罗涛
 */

public class SystemFilter implements Filter {

    Logger logger = LoggerFactory.getLogger(SystemFilter.class);


    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        if (!(servletRequest instanceof HttpServletRequest) || !(servletResponse instanceof HttpServletResponse)) {
            throw new ServletException("OncePerRequestFilter just supports HTTP requests");
        }
        HttpServletRequest httpRequest = (HttpServletRequest) servletRequest;
        HttpServletResponse httpResponse = (HttpServletResponse) servletResponse;
        HttpSession session = httpRequest.getSession(true);

        StringBuffer url = httpRequest.getRequestURL();
        String[] strs = ProsReader.getString("INDICATION_APP_NAME").split("\\|");
        if (strs != null && strs.length > 0) {
            for (String str : strs) {
                if (url.indexOf(str) >= 0) {
                    filterChain.doFilter(servletRequest, servletResponse);
                    return;
                }
            }
        }
        Object object = session.getAttribute(SessionConstants.SESSION_USER);
        User user = object == null ? null : (User) object;
        if (user == null) {
            boolean isAjaxRequest = isAjaxRequest(httpRequest);
            if (isAjaxRequest) {
                httpResponse.setCharacterEncoding("UTF-8");
                httpResponse.sendError(HttpStatus.UNAUTHORIZED.value(),
                        "您已经太长时间没有操作,请刷新页面");
            }
            httpResponse.sendRedirect("/page/login/user_login");
            return;
        }
        filterChain.doFilter(servletRequest, servletResponse);
        return;
    }

    /**
     * 判断是否为Ajax请求
     *
     * @param request HttpServletRequest
     * @return 是true, 否false
     */
    public static boolean isAjaxRequest(HttpServletRequest request) {
        return request.getRequestURI().startsWith("/api");
//        String requestType = request.getHeader("X-Requested-With");
//        return requestType != null && requestType.equals("XMLHttpRequest");
    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
            /*如果需要注入，请取消注释*/
//           ServletContext servletContext = filterConfig.getServletContext();
//            WebApplicationContext applicationContext = (WebApplicationContext) servletContext.
//                    getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
//            if (null == topConstantsImpl) {
//                //从Spring AC 中加载app configuration对象
//                topConstantsImpl = applicationContext.getBean(TopConstantsImpl.class);
//        }
    }

    @Override
    public void destroy() {
        //To change body of implemented methods use File | Settings | File Templates.
    }


}

 <!-- 判断用户session 是否过期，如果过期，让用户重新登录-->
    <!--<filter>-->
        <!--<filter-name>SystemFilter</filter-name>-->
        <!--<filter-class>com.yitaosoft.common.filter.SystemFilter</filter-class>-->
    <!--</filter>-->
    <!--<filter-mapping>-->
        <!--<filter-name>SystemFilter</filter-name>-->
        <!--<url-pattern>/*</url-pattern>-->
    <!--</filter-mapping>-->