Pushlet

在项目中遇到需要实现类似 facebook 消息推送的功能, 也就是服务器端将未读的系统消息条数推送给前台用户(秒级), 即用户在前台页面可以实时的看到最新的系统消息, 经过调研决定使用 Pushlet (http://www.pushlets.com/)  来实现.

      首先, 由于 Pushlet 自己产生的 sessionid 是个随机数, 当后台向前台推送消息时无法和当前登录用户联系起来, 因此我们需要修改 Pushlet 产生 sessionid 的方法. 具体来说就是在

      nl.justobjects.pushlet.core.SessionManager 中修改方法 public Session createSession(Event anEvent) throws PushletException

      修改后的代码为

public Session createSession(Event anEvent) throws PushletException {
        // Trivial
        //return Session.create(createSessionId());
        //return Session.create(createSessionId(), anEvent);
        return Session.create(anEvent.getField("userid", "visitor"));
    }

      

       其次, 在前台的 ajax-pushlet-client.js 增加几行代码用来向后台传用户登录 id

      在此代码后面加上

       // Construct base URL for GET
       var url = PL.pushletURL + '?p_event=' + anEvent;

var userid = getMenuValue("userid");
if (anEvent == 'join' || anEvent == 'join-listen') {
 url = url + '&userid=' + userid;
}

      对 Pushlet 的源代码改造完成, 需要对其重新编译生成 jar 文件后加入到项目 lib 中去

      接下来就是编写 servlet 来获取当前登录用户有多少未读消息

public class NotifyPushletServlet extends HttpServlet{
    /**
     *
     */
    private static final long serialVersionUID = 1L;
    private static SystemService systemService;

    public SystemService getSystemService() {
        return systemService;
    }

    public void setSystemService(SystemService systemService) {
        NotifyPushletServlet.systemService = systemService;
    }


    @Override
    public void init(ServletConfig config) throws ServletException {
        // TODO Auto-generated method stub
        super.init(config);
        ServletContext servletContext = this.getServletContext();
        WebApplicationContext wac = null;
        wac = WebApplicationContextUtils.getRequiredWebApplicationContext(servletContext);
        this.setSystemService((SystemService) wac.getBean("systemService"));
    }

    static public class Pushlet extends EventPullSource {
        @Override
        protected long getSleepTime() {
            return 5000;
        }

        @Override
        protected Event pullEvent() {
            System.out.println(new Date());
            Event event = Event.createDataEvent("/notifynum");
            Session[] sessions = SessionManager.getInstance().getSessions();
            if (sessions.length > 0) {
                StringBuilder str = new StringBuilder("");
                for (int i = 0; i < sessions.length; i++) {
                    if (sessions[i].getId().equals("guest")) continue;
                    if (!str.toString().equals("")) str.append(",");
                    str.append("'" + sessions[i].getId() + "'");
                }
                if (!str.toString().equals("")) {
                    List<?> list = systemService.findNotReadNotificationNumOnline(str.toString());
                    if (list != null && list.size() > 0) {
                        Object[] obj = null;
                        String userid = null, num = null;
                        for (int i = 0; i < list.size(); i++) {
                            obj = (Object[]) list.get(i);
                            userid = obj[0].toString();
                            num = obj[1].toString();
                            System.out.println("userid = " + userid + ", num = " + num);
                            event.setField(userid, num);
                        }
                    }
                }
            }

            return event;
        }

    }
}

       最后在前台只接受并显示当前用户自己对应的未读的消息条数

 <script type="text/javascript">
    var userid = getMenuValue("userid");
    PL._init();
PL.joinListen('/notifynum');
function onData(event) {
    var num = event.get(userid);
    if (num > 0) {
        document.getElementById('desktopnotify').innerHTML = num;
        document.getElementById('desktopnotify').style.display='';
    } else {
        document.getElementById('desktopnotify').style.display='none';
    }
}
lt;/script>
原文：http://blog.csdn.net/dataminer_2007/article/details/7653283