<form name="xx" action="<c:url value=‘/Up3Servlet‘/>" method="post" enctype="multipart/form-data">
    <table id="tb" border="1">
        <tr>
            <td>
                File：
            </td>
            <td>
                <input type="file" name="file">
                <button onclick="_del(this);">删除</button>
            </td>
        </tr>
    </table>
    <br/>
    <input type="button" onclick="_submit();" value="上传">
    <input onclick="_add();" type="button" value="增加">
    </form>
  </body>
  <script type="text/javascript">
      function _add(){
          var tb = document.getElementById("tb");
          //写入一行
          var tr = tb.insertRow();
          //写入列
          var td = tr.insertCell();
           //写入数据
          td.innerHTML="File：";
          //再声明一个新的td
          var td2 = tr.insertCell();
          //写入一个input
          td2.innerHTML=‘<input type="file" name="file"/><button onclick="_del(this);">删除</button>‘;
      }
      function _del(btn){
          var tr = btn.parentNode.parentNode;
          //alert(tr.tagName);
          //获取tr在table中的下标
          var index = tr.rowIndex;
          //删除
          var tb = document.getElementById("tb");
          tb.deleteRow(index);
      }
      function _submit(){
          //遍历所的有文件
          var files = document.getElementsByName("file");
          if(files.length==0){
              alert("没有可以上传的文件");
              return false;
          }
          for(var i=0;i<files.length;i++){
              if(files[i].value==""){
                  alert("第"+(i+1)+"个文件不能为空");
                  return false;
              }
          }
        document.forms[‘xx‘].submit();
      }
  </script>
</html>

package cn.hx.servlet;
import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;
import java.util.UUID;

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

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import org.apache.commons.io.FileUtils;

public class UpImgServlet extends HttpServlet {

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        request.setCharacterEncoding("UTF-8");
        String path = getServletContext().getRealPath("/up");
        DiskFileItemFactory disk = 
                new DiskFileItemFactory(1024*10,new File("d:/a"));
        ServletFileUpload up = new ServletFileUpload(disk);
        try{
            List<FileItem> list = up.parseRequest(request);
            //只接收图片*.jpg-iamge/jpege.,bmp/imge/bmp,png,
            List<String> imgs = new ArrayList<String>();
            for(FileItem file :list){
                if(file.getContentType().contains("image/")){
                    String fileName = file.getName();
                    fileName = fileName.substring(fileName.lastIndexOf("\\")+1);
                    
                    //获取扩展
                    String extName = fileName.substring(fileName.lastIndexOf("."));//.jpg
                    //UUID
                    String uuid = UUID.randomUUID().toString().replace("-", "");
                    //新名称
                    String newName = uuid+extName;         //在这里用UUID来生成新的文件夹名字，这样就不会导致重名
                    
                    
                    FileUtils.copyInputStreamToFile(file.getInputStream(),
                            new File(path+"/"+newName));
                    //放到list
                    imgs.add(newName);
                }
                file.delete();
            }
            request.setAttribute("imgs",imgs);
            request.getRequestDispatcher("/jsps/imgs.jsp").forward(request, response);
        }catch(Exception e){
            e.printStackTrace();
        }
    
    }

}