AJAX基础教程－7 AutoRefresh Page

js 代码

<script type=< span="">"text/javascript">
var xmlHttp;
    function createXMLHttpRequest() {
        if (window.ActiveXObject) {
        xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
        }
        else if (window.XMLHttpRequest) {
        xmlHttp = new XMLHttpRequest();
        }
    }
    function doStart() {
        createXMLHttpRequest();
        var url = "DynamicUpdate?task=reset";
        xmlHttp.open("GET", url, true);
        xmlHttp.onreadystatechange = startCallback;
        xmlHttp.send(null);
    }
    function startCallback() {
        if (xmlHttp.readyState == 4) {
            if (xmlHttp.status == 200) {
            setTimeout("pollServer()", 5000);
            refreshTime();
            }
        }
    }

    function pollServer() {
        createXMLHttpRequest();
        var url = "DynamicUpdateServlet?task=foo";
        xmlHttp.open("GET", url, true);
        xmlHttp.onreadystatechange = pollCallback;
        xmlHttp.send(null);
    }

    function refreshTime(){
        var time_span = document.getElementById("time");
        var time_val = time_span.innerHTML;
        var int_val = parseInt(time_val);
        var new_int_val = int_val - 1;
        if (new_int_val > -1) {
        setTimeout("refreshTime()", 1000);
        time_span.innerHTML = new_int_val;
        } else {
        time_span.innerHTML = 5;
        }
    }

    function pollCallback() {
        if (xmlHttp.readyState == 4) {
            if (xmlHttp.status == 200) {
                var message =
                xmlHttp.responseXML
                .getElementsByTagName("message")[0].firstChild.data;
                if (message != "done") {
                var new_row = createRow(message);
                var table = document.getElementById("dynamicUpdateArea");
                var table_body =
                table.getElementsByTagName("tbody").item(0);
                var first_row =
                table_body.getElementsByTagName("tr").item(1);
                table_body.insertBefore(new_row, first_row);
                setTimeout("pollServer()", 5000);
                refreshTime();
                }
            }
        }
    }

    function createRow(message) {
        var row = document.createElement("tr");
        var cell = document.createElement("td");
        var cell_data = document.createTextNode(message);
        cell.appendChild(cell_data);
        row.appendChild(cell);
        return row;
    }
</script>

java 代码

package ajax.foundations_of_ajax;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class DynamicUpdateServlet extends HttpServlet {
    private int counter = 1;

    /**
     * Handles the HTTP GET method.
     *
     * @param request
     *            servlet request
     * @param response
     *            servlet response
     */
    protected void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        String res = "";
        String task = request.getParameter("task");
        String message = "";
        if (task.equals("reset")) {
            counter = 1;
        } else {
            switch (counter) {
            case 1:
                message = "Steve walks on stage";
                break;
            case 2:
                message = "iPods rock";
                break;
            case 3:
                message = "Steve says Macs rule";
                break;
            case 4:
                message = "Change is coming";
                break;
            case 5:
                message = "Yes, OS X runs on Intel - has for years";
                break;
            case 6:
                message = "Macs will soon have Intel chips";
                break;
            case 7:
                message = "done";
                break;
            }
            counter++;
        }
        res = "<message></message>" + message + "";
        PrintWriter out = response.getWriter();
        response.setContentType("text/xml");
        response.setHeader("Cache-Control", "no-cache");
        out.println("<response></response>");
        out.println(res);
        out.println("");
        out.close();
    }
}