Tomcat提供了一种高级IO，可以实现Comet的功能。
Servlet需要实现 CometProcessor接口，并且设置Tomcat连接器为org.apache.coyote.http11.Http11NioProtocol

下面代码实现的功能还是获取服务器JVM信息。

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;
import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.catalina.comet.CometEvent;
import org.apache.catalina.comet.CometProcessor;
@WebServlet(urlPatterns = { "/comet.do" })
public class InitServlet extends HttpServlet implements CometProcessor, Runnable {
Queue<HttpServletResponse> queue = new ConcurrentLinkedQueue<HttpServletResponse>();
ScheduledExecutorService singleThread = Executors.newSingleThreadScheduledExecutor();
{
singleThread.scheduleWithFixedDelay(this, 3, 3, TimeUnit.SECONDS);
}
private String htmlEscape(String message) {
return "\n";
}
private String getJVMInfo() {
long useMemory = Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory();
useMemory = useMemory / 1024;
return "已用内存:" + String.valueOf(useMemory) + "K";
}
@Override
public void run() {
System.out.println("发送广播通知");
String data = "广播通知\n" + new Date() + "\n" + getJVMInfo();
for (HttpServletResponse response : queue) {
try {
response.setContentType("text/html;charset=UTF-8");
PrintWriter writer = response.getWriter();
writer.println(htmlEscape(data));
writer.flush();
} catch (IOException e) {
queue.remove(response);
e.printStackTrace();
}
}
}
@Override
public void event(CometEvent event) throws IOException, ServletException {
HttpServletRequest request = event.getHttpServletRequest();
HttpServletResponse response = event.getHttpServletResponse();
String name = request.getParameter("name");
if (event.getEventType() == CometEvent.EventType.BEGIN) {
event.setTimeout(Integer.MAX_VALUE);
queue.add(response);
} else if (event.getEventType() == CometEvent.EventType.ERROR) {
queue.remove(event);
event.close();
} else if (event.getEventType() == CometEvent.EventType.END) {
queue.remove(event);
event.close();
} else if (event.getEventType() == CometEvent.EventType.READ) {
}
}
}

前台页面：

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

<html>

<head>

<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">

<script type="text/javascript"

    src="http://code.jquery.com/jquery-2.0.3.min.js"></script>

<script type="text/javascript">

    var connection = {

        iframe : false,

        server : 'comet.do',

        init : function() {

            connection.iframe = document.createElement('iframe');

            connection.iframe.setAttribute("id", "comet_iframe");

            with (connection.iframe.style) {

                left = top = "-100px";

                height = width = "1px";

                visibility = "hidden";

                display = 'none';

            }

            $('body').append(connection.iframe)

        },

        request : function() {

            var name = $('#name').val();

            connection.iframe.setAttribute("src", connection.server + '?name='

                    + name);

        },

        callback : function(data) {

            $('#content').html(data);

        }

    }

    $(document).ready(function() {

        connection.init();

    });

</script>

</head>

<body>

    <input type="text" id="name" />

    <input type="button" value="start" onclick="connection.request();" />

    <div id="content"></div>

</body>

</html>

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