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);
}
}
