需求：

统计某应用的在线用户数

实现方案：

1.基于session监听(复杂麻烦)

2.基于org.apache.catalina.Manager(依赖)

采用第二种的实现如下：

private int activeUserNumber(HttpServletRequest request) {	int activeSessions = 0;	try {		if (request instanceof RequestFacade) {			Field requestField = request.getClass().getDeclaredField(					"request");			requestField.setAccessible(true);			Request req = (Request) requestField.get(request);			org.apache.catalina.Context context = req.getContext();			Manager manager = context.getManager();			activeSessions = manager.getActiveSessions();		}	} catch (Exception e) {		e.printStackTrace();	}	log.info("users:{}", activeSessions);	return activeSessions;}private List
    
      activeUsers(HttpServletRequest request) {	List
     
       list = new ArrayList
      
       ();	try {		if (request instanceof RequestFacade) {			Field requestField = request.getClass().getDeclaredField(					"request");			requestField.setAccessible(true);			Request req = (Request) requestField.get(request);			org.apache.catalina.Context context = req.getContext();			Manager manager = context.getManager();			Session[] sessions = manager.findSessions();			for (Session session : sessions) {				 //your			}		}	} catch (Exception e) {		e.printStackTrace();	}	log.info("users:{}", list);	return list;}