@WebListener 
public class OnLineCount implements HttpSessionListener { 
  public int count=0;//記錄session的數(shù)量 
  //監(jiān)聽session的創(chuàng)建,synchronized 防并發(fā)bug 
  public synchronized void sessionCreated(HttpSessionEvent arg0) { 
    System.out.println("【HttpSessionListener監(jiān)聽器】count++ 增加"); 
    count++; 
    arg0.getSession().getServletContext().setAttribute("count", count); 
  } 
  @Override 
  public synchronized void sessionDestroyed(HttpSessionEvent arg0) {//監(jiān)聽session的撤銷 
    System.out.println("【HttpSessionListener監(jiān)聽器】count-- 減少"); 
    count--; 
    arg0.getSession().getServletContext().setAttribute("count", count); 
  } 
} 

@RequestMapping("/count") 
@ResponseBody 
public String count(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse){ 
  Object count=httpServletRequest.getServletContext().getAttribute("count"); 
  return "count : "+count; 
} 

@Controller 
public class IndexController { 
  @RequestMapping("/count") 
  @ResponseBody 
  public String count(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse){ 
    HttpSession session = httpServletRequest.getSession(); 
    Object count=session.getServletContext().getAttribute("count"); 
    return "count : "+count; 
  } 
} 

@Controller 
public class IndexController { 
  @RequestMapping("/count") 
  @ResponseBody 
  public String number(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse){ 
    try{ //把sessionId記錄在瀏覽器 
      Cookie c = new Cookie("JSESSIONID", URLEncoder.encode(httpServletRequest.getSession().getId(), "utf-8")); 
      c.setPath("/"); 
      //先設(shè)置cookie有效期為2天，不用擔(dān)心，session不會保存2天 
      c.setMaxAge( 48*60 * 60); 
      httpServletResponse.addCookie(c); 
    }catch (Exception e){ 
      e.printStackTrace(); 
    } 
    HttpSession session = httpServletRequest.getSession(); 
    Object count=session.getServletContext().getAttribute("count"); 
    return "count : "+count; 
  } 
}