长轮询的简单实现

<servlet>

　　<servlet-name>polling</servlet-name>

　　<servlet-class>com.xxx.longpolling.PollingServlet</servlet-class>

<async-supported>true</async-supported> </servlet>

public class PollingServlet extends HttpServlet { private static final long serialVersionUID = 4793060102193587649L; public static DateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); //内存存储所有请求的request客户端 public static Map<String, PollingClient> client = new ConcurrentHashMap<String, PollingClient>(); static { //启动一个线程，扫描，关闭所有超时的连接 new Timer().schedule(new TimerTask() { @Override public void run() { long current = System.currentTimeMillis(); for (Map.Entry<String, PollingClient> entry : client.entrySet()) { PollingClient pollingClient = entry.getValue(); if (pollingClient == null) return; if (current - pollingClient.vistTime > 20 * 1000) { pollingClient.complete(); client.remove(entry.getKey()); } } } }, 10, 5000); } @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { String actionType = req.getParameter("actionType"); System.out.print("actionType:" + actionType); //poll主题 if ("poll".equalsIgnoreCase(actionType)) { String topic = req.getParameter("topic"); pollTopic(req, resp, topic); } //管理后台,改变数据 else if ("set".equalsIgnoreCase(actionType)) { String topic = req.getParameter("topic"); String msg = req.getParameter("msg"); changeTopic(topic, msg); resp.getWriter().print("ok"); } } /** * poll数据，缓存请求的对象 * @param req * @param resp * @param topic */ private void pollTopic(HttpServletRequest req, HttpServletResponse resp, String topic) { final AsyncContext asyncContext = req.startAsync(); asyncContext.setTimeout(0L); client.put(topic, new PollingClient(asyncContext, topic)); } /** * 数据发生变化 * @param topic * @param msg */ private void changeTopic(String topic, String msg) { PollingClient pollingClient = client.get(topic); if (pollingClient != null) pollingClient.response(msg); } private static class PollingClient { public AsyncContext asyncContext; public String topic; public long vistTime; PollingClient(AsyncContext asyncContext, String topic) { this.topic = topic; this.asyncContext = asyncContext; this.vistTime = System.currentTimeMillis(); } //主动关闭连接 private void complete() { response("connect end"); asyncContext.complete(); } //响应数据 private void response(String message) { Map<String, Object> content = new HashMap<String, Object>(); content.put("messages", message); content.put("topic", topic); try { HttpServletResponse response = (HttpServletResponse) asyncContext.getResponse(); PrintWriter writer = response.getWriter(); response.setHeader("Content-type", "text/html;charset=UTF-8"); writer.println(format.format(new Date()) + ",receive:" + content + "<br/>"); writer.flush(); } catch (Exception se) { } } } }