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文件上传过程中，如果我们能看到进度条会更好，实现思路是服务器端用监听器实时监听进度并存入session，客户端异步请求服务器端获得上传进度，并进行效果渲染。
效果图：
服务器端servlet:
public class UploadServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { //取出监听器MyProgress在session中保存的进度信息 String progress=(String) req.getSession().getAttribute("progress"); //响应 resp.getWriter().print(progress); //清除session中保存的数据 // req.getSession().removeAttribute("progress"); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { req.setCharacterEncoding("UTF-8"); DiskFileItemFactory factory=new DiskFileItemFactory(); ServletFileUpload upload=new ServletFileUpload(factory); upload.setProgressListener(new MyProgressListener(req)); try { List<FileItem> list = upload.parseRequest(req); for (FileItem fileItem : list) { if (fileItem.isFormField()) {//普通表单 }else{//上传文件 String path=req.getRealPath("uploads"); String fileName=fileItem.getName(); File file=new File(path, fileName); fileItem.write(file); System.out.println("成功上传文件："+fileName); } } } catch (Exception e) { System.out.println("文件上传发生错误！"); e.printStackTrace(); } } }
服务器端监听器：
public class MyProgressListener implements ProgressListener { private HttpSession session; public MyProgressListener(HttpServletRequest request){ session = request.getSession(); } @Override public void update(long pBytesRead, long pContentLength, int pItems) { //将数据进行格式化 //已读取数据由字节转换为M double readM=pBytesRead/1024.0/1024.0; //已读取数据由字节转换为M double totalM=pContentLength/1024.0/1024.0; //已读取百分百 double percent=readM/totalM; //格式化数据 //已读取 String readf=dataFormat(pBytesRead); //总大小 String totalf=dataFormat(pContentLength); //进度百分百 NumberFormat format=NumberFormat.getPercentInstance(); String progress=format.format(percent); //将信息存入session session.setAttribute("progress", progress); //打印消息到控制台 System.out.println("pBytesRead===>"+pBytesRead); System.out.println("pContentLength==>"+pContentLength); System.out.println("pItems===>"+pItems); System.out.println("readf--->"+readf); System.out.println("totalf--->"+totalf); System.out.println("progress--->"+progress); } /** * 格式化读取数据的显示 * @param data要格式化的数据 单位byte * @return 格式化后的数据，如果小于1M显示单位为KB，如果大于1M显示单位为M */ public String dataFormat(double data){ String formdata=""; if (data>=1024*1024) {//大于等于1M formdata=Double.toString(data/1024/1024)+"M"; }else if(data>=1024){//大于等于1KB formdata=Double.toString(data/1024)+"KB"; }else{//小于1KB formdata=Double.toString(data)+"byte"; } return formdata.substring(0, formdata.indexOf(".")+2); } }
客户端：
<html> <head> <base href="<%=basePath%>"> <title>带进度条的文件上传效果</title> <meta http-equiv="pragma" content="no-cache"> <meta http-equiv="cache-control" content="no-cache"> <meta http-equiv="expires" content="0"> <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> <meta http-equiv="description" content="This is my page"> <style type="text/css"> #progressBar{width: 300px;height: 20px;border: 1px #EEE solid;} #progress{width: 0%;height: 20px;background-color: lime;} </style> <script type="text/javascript" src="js/jquery-1.4.2.js"></script> <script type="text/javascript"> function upload(){ $("#f1").submit(); var pro=null; pro=setInterval(function(){ $.get("UploadServlet","",function(data){ if(data=='100%'){ clearInterval(pro); $("#proInfo").text("上传进度：100%"); //更新进度条 $("#progress").width("100%"); }else{//正在上传 //更新进度信息 $("#proInfo").text("上传进度："+data); //更新进度条 $("#progress").width(data); } }); },200); } </script> </head> <body> <iframe name="aa" style="display: none;"></iframe> <h2>带进度条的文件上传效果</h2> <form target="aa" id="f1" action="UploadServlet" method="post" enctype="multipart/form-data"> 文件：<input name="file" type="file"> <input type="button" value="上传" onclick="upload();"> <div id="progressBar"> <div id="progress"></div> </div> <span id="proInfo">上传进度：0%</span> </form> </body> </html>
说明：为了让上传后该页面不跳转，我们可以让表单跳转至一个隐藏的iframe。