Session的有效期设置

方式一：
 在web.xml中设置session-config如下：
 <session-config>
  <session-timeout>2</session-timeout>
 </session-config>

即客户端连续两次与服务器交互间隔时间最长为2分钟，2分钟后session.getAttribute()获取的值为空

 API信息：
  session.getCreationTime()   获取session的创建时间
  session.getLastAccessedTime()  获取上次与服务器交互时间
  session.getMaxInactiveInterval() 获取session最大的不活动的间隔时间，以秒为单位120秒。

<!-- 登录状态过滤,可以过滤掉不需要进行超时验证的url -->
<filter>
<filter-name>loginFilter</filter-name>
<filter-class>com.software.filter.LoginFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>loginFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>

<!---以上代码指明具体的路径，具体的代码见附录>

方式二：
 在Tomcat的/conf/web.xml中session-config,默认值为：30分钟
 <session-config>
        <session-timeout>30</session-timeout>
    </session-config>

方式三：
 在Servlet中设置
  HttpSession session = request.getSession();
  session.setMaxInactiveInterval(60);//单位为秒

说明：
 1.优先级：Servlet中API设置 > 程序/web.xml设置 > Tomcat/conf/web.xml设置
 2.若访问服务器session超时（本次访问与上次访问时间间隔大于session最大的不活动的间隔时间）了，即上次会话结束，但服务器与客户端会产生一个新的会话，之前的session里的属性值全部丢失，产生新的sesssionId
 3.客户端与服务器一次有效会话（session没有超时），每次访问sessionId相同，若代码中设置了session.setMaxInactiveInterval()值，那么这个session的最大不活动间隔时间将被修改，并被应用为新值。
 4.Session的销毁（代表会话周期的结束）：在某个请求周期内调用了Session.invalidate()方法，此请求周期结束后，session被销毁；或者是session超时后自动销毁；或者客户端关掉浏览器
 5.对于JSP，如果指定了<%@ page session="false"%>，则在JSP中无法直接访问内置的session变量，同时也不会主动创建session，因为此时JSP未自动执行request.getSession()操作获取session。

附录：

package com.software.filter;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.HashSet;
import java.util.Set;

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 org.apache.log4j.Logger;

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONObject;
import com.software.pojo.LoginInfo;
import com.software.util.AjaxResultHelper;

public class LoginFilter implements Filter {
    
    String [] noFilter = {"/collect/collectSensorData","/user/registerpage","/user/register","/user/checklogin","/system/login","/system/registerpage","/breedingLog/loadImages",
            "/expert/expertList","/expert/getNewQuestionsByPage","/expert/getHostQuestionsByPage","/product/productList","/product/productDetail","/product/feedList","/product/feedDetail",
            "/product/drugList","/product/drugDetail","/product/seedList","/product/seedDetail","/product/commonList","/product/commonDetail","/user/userInfo","/user/getDealtAnswer",
            "/user/getWaitReply"};
    private Set<String> noFilterSet = new HashSet<String>();
    private Logger log = Logger.getLogger(LoginFilter.class);
    @Override
    public void destroy() {
        

    }

    @Override
    public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2)
            throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest) arg0;
        HttpServletResponse response = (HttpServletResponse) arg1;
        String nofilterpage = request.getServletPath();
        //log.info("nofilterpage:"+nofilterpage);
        if(noFilterSet.contains(nofilterpage) || nofilterpage.startsWith("/res") || nofilterpage.equals("/index.jsp")){//放行
        //放行
            //log.info("nofilterpage:"+nofilterpage);
            arg2.doFilter(request, response);
        }else{    
            LoginInfo loginInfo =(LoginInfo) request.getSession().getAttribute("loginInfo");
            if(null == loginInfo ){
                
                JSONObject responseJSONObject = (JSONObject)JSON.toJSON(AjaxResultHelper.getErrorRes(0,"未登录",null,0));
                PrintWriter out = null;
                response.setCharacterEncoding("UTF-8");
                try {  
                    out = response.getWriter();  
                    out.append(responseJSONObject.toString());   
                } catch (IOException e) {  
                    e.printStackTrace();  
                } finally {  
                    if (out != null) {  
                        out.close();  
                    }  
                }  
//                String path =  request.getContextPath();
//                String basePath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + path;
//                response.sendRedirect(basePath + "/system/login");
//                response.sendRedirect(basePath + "/system/overtime");
            }else{
                AjaxResultHelper.getSuccessRes();
                arg2.doFilter(request, response);
            }
        }

    }

    @Override
    public void init(FilterConfig arg0) throws ServletException {
        for(String s:noFilter){
            noFilterSet.add(s);
        }

    }

}