问个jquery.comet问题

jquery.comet的后台SERVLET如何实现？
哪位高手指点指点，提供点有用的实现代码也行
官方的例子前台代码是这样的      <script type="text/javascript" src="json2.js"></script>
    <script type="text/javascript" src="jquery.js"></script>
<script type="text/javascript" src="jquery.comet.js"></script>
    <script type="text/javascript">
      function timeCallback(msg) {
      alert(msg.data);
        $("#counter_output").text(msg.data);
      };
      function msgCallback(msg) {
        $("#echo_output").text(msg.data);
      };
      function sendMessage() {
        $.comet.publish("/test/msg",$("#echo_input").val());
      };
      $(document).ready(function() {
        $.comet.init("/comet/servlet/CometServlet");
        $.comet.subscribe("/test/msg", msgCallback);
      });
    </script><div class="container">
                <div id="echo_output" class="output" style="height:3ex"></div>
                <div class="input">
                <div>
                        Input:
                                <input id="echo_input" type="text">
                                <input class="button" type="submit" onclick="javascript:sendMessage();" value="publish"/>
                </div>
        </div>
        </div>