Ajax + java Servlet 制作Web进度条

package ajax_servlet_1;

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;

// https://www.cnblogs.com/lihuiyy/archive/2012/05/24/2516627.html

public class ProcessServlet2 extends HttpServlet {
    private static final long serialVersionUID = 5280356329609002908L;
    
    private static final String CONTENT_TYPE = "text/xml; charset=UTF-8";
//设置返回响应的ContentType
    private int count = 1;// 全局变量计数器
    /**
     *当前Servlet对象构造方法
     */
    public ProcessServlet2() {
        super();
    }
    /**
     *当前Servlet销毁时的操作。
*/
    public void destroy() {
        super.destroy();
    }
    /**
     *当前Servlet的doGet方法。

     *
     *当客户端表单的“method”类型为“get”时，调用此方法
     *
     * @param request客户端请求对象
     * @param response 服务器响应对象
     * @throws ServletException 发生ServeltException时抛出
     * @throws IOException发生IOException时抛出
     */
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        System.out.println("*********************doGet()**********");
        response.setContentType(CONTENT_TYPE); //设置服务器响应类型
        response.setHeader("Cache-Control","no-cache"); //页面不记录缓存
        String flag = request.getParameter("flag"); //操作类型
        StringBuffer xml=
//            new StringBuffer("");
            new StringBuffer("");
        //记录返回的xml串
        if("start".equals(flag)) { //第一次创建
//            xml.append("1");
            count = 1;
        } else {
            String proportion = "";
            try
            { 
                
                switch(count) { //根据计数器的值，设置显示当前进度的百分比
                  case 1:
                      proportion="10"; 
                      break;
                  case 2:
                      proportion="20";  
                      break;
                  case 3:
                      proportion="30"; 
                      break;
                  case 4:
                      proportion="40"; 
                      break;
                  case 5:
                      proportion="50"; 
                      break;
                  case 6:
                      proportion="60"; 
                      break;
                  case 7:
                      proportion="70"; 
                      break;
                  case 8:
                      proportion="80"; 
                      break;
                  case 9:
                      proportion="90"; 
                      break;
                  case 10:
                      proportion="100"; 
                      break;
                }
                
            }
            catch(InterruptedException e)
            { 
                e.printStackTrace(); 
            } 
            count++;
            xml.append("").append(proportion).append("");
        }
        xml.append("");
        PrintWriter out = response.getWriter();
        out.println(xml.toString()); //返回生成的XML串
        out.flush(); //输出流刷新
        out.close(); //关闭输出流
        System.out.println("*********** " + xml.toString());
    }

    /**
     * 初始化servlet. 

     * @throws ServletException 发生ServletExcpetio异常时抛出
     */
    public void init() throws ServletException {
    }
}

ProcessServletajax_servlet_1.ProcessServletProcessServlet/ProcessServletProcessServlet2ajax_servlet_1.ProcessServlet2ProcessServlet2/ProcessServlet2index2.jsp