关于文件上传服务器的知识，前端是type = “file”标签，有预览功能

前端html

<div class="layui-col-md10" style="text-align: center;">
      <label class = "layui-btn">
         请上传图片
         <input type="file" name="file10" id="pushBodyImgUrl10" value='img' onchange="UI.pushBodyImg()" style="display: none"/>
      </label>
   <div style="margin-top: 2%">
      <button onclick="UI.clearImg()" class="layui-btn">清空</button>
      <button onclick="UI.pushImgToAll()" class="layui-btn">群发</button>
   </div>
   <div style="text-align: center">
      <br><br>
      <img src="" id="img01" width="350" class="hide" value=""/>
   </div>
</div>

JS：
//将图片上传 

pushBodyImg:function(){
   var file = $("#pushBodyImgUrl10")[0].files[0];
   var objUrl = UI.getObjectURL(file);
   //var objUrl = $("#pushBodyImgUrl10")[0].files[0];
   var size = $("#pushBodyImgUrl10")[0].files[0].size;
   console.log("size = "+size) ;
   console.log("objUrl = "+objUrl) ;
   if (objUrl)
   {
      $("#img01").attr("src", objUrl);//进行图片预览
      console.log("objUrl = "+objUrl) ;
      $("#img01").removeClass("hide");
   }
},
//得到图片的Blob格式，兼容不同的浏览器

getObjectURL:function(file){
      var url = null ;
      if (window.createObjectURL!=undefined)
      { // basic
         url = window.createObjectURL(file) ;
      }
      else if (window.URL!=undefined)
      {
         // mozilla(firefox)
         url = window.URL.createObjectURL(file) ;
      }
      else if (window.webkitURL!=undefined) {
         // webkit or chrome
         url = window.webkitURL.createObjectURL(file) ;
      }
      return url ;

},
//清空现有图片

clearImg:function(){
   $("#pushBodyImgUrl10").val("");
   $("#img01")[0].src="";
   $("#img01").addClass("hide");
},
//进行图片上传

pushImgToAll:function() {
   var title = $("#img01")[0].src;
   var bodyImg = $("#pushBodyImgUrl10").val();
   if(bodyImg ==''){
      layui.layer.alert("请先上传图片");
      return false;
   }
   var sizeImg = $("#pushBodyImgUrl10")[0].files[0].size;
   var nameImg = bodyImg;
   var sfIndexImg=nameImg.lastIndexOf(".");//后缀位置的.的位置
   var extImg=nameImg.substring(sfIndexImg,nameImg.length).toUpperCase();//截取后缀
   if(extImg !='.PNG' && extImg !='.GIF' && extImg !='.JPG' && extImg !='.JPEG' && extImg !='.BMP'){
      layui.layer.alert("文件类型错误,请上传正确图片类型(png、gif、jpg、jpeg、bmp)");
      return false;
   }
   if(sizeImg/1024/1024>5){
      layui.layer.alert("图片大小不能大于5M");
      return false;
   }
   var img = $("#pushBodyImgUrl10")[0].files[0];
   var formData = new FormData();
   formData.append("file",img);//这个是一个参数
   $.ajax({
      url : '/mp/filesToAll',
      method : 'POST',
      processData: false,
      contentType:false,
      data : formData,
      success : function(result) {
         if (result.resultCode == 1) {
            layui.layer.alert("群发成功");
            $("#pushBodyImgUrl10").val("");
            $("#img01")[0].src="";
            $("#img01").addClass("hide");
         } else {
            layui.layer.alert("群发失败");
         }
      }
   })
},

后端JAVA

@RequestMapping(value="/filesToAll")
@ResponseBody
public JSONMessage imgToAll(HttpServletResponse response, @RequestParam(required = false)MultipartFile file){
   String domain=appConfig.getUploadDomain();
   String title = "";
   String extImg = "";
   if (file != null){
      String uploadFileUrl = FileUtil.fileToUploadDomain(domain,file);
      title = uploadFileUrl;
      int sfIndexImg=title.lastIndexOf(".");//后缀位置的.的位置
      extImg=title.substring(sfIndexImg,title.length()).toUpperCase();
   }
   User user = getUser();
   List<Fans> fansList = getFriendsManager().getFansList(getUser().getUserId());
   List<Integer> toUserIdList = Lists.newArrayList();
   for (Fans fans : fansList) {
      toUserIdList.add(fans.getToUserId());
   }
   MessageBean mb = new MessageBean();
   mb.setContent(title);
   mb.setFromUserId(user.getUserId() + "");
   mb.setFromUserName(user.getNickname());
   mb.setTimeSend(DateUtil.currentTimeSeconds());
   mb.setMsgType(2);// 广播消息
   if(extImg.equalsIgnoreCase(".mp4")){
      mb.setType(6);//type是6表明是视频
   }else{
      mb.setType(2);//type是2表明是图片
   }
   mb.setMessageId(StringUtil.randomUUID());
   try {
      ThreadUtil.executeInThread(new Callback() {
         @Override
         public void execute(Object obj) {
            KXMPPServiceImpl.getInstance().send(mb,toUserIdList);//给各个用户发消息
         }
      });
   } catch (Exception e) {
      System.out.println(user.getUserId() + "：推送失败");
      return JSONMessage.failure(e.getMessage());
   }
   return JSONMessage.success();
}

public static String fileToUploadDomain(String domain,MultipartFile multipartFile){
      String newUrl=null;
      try {
         // 换行符
         final String newLine = "
";
         final String boundaryPrefix = "--";
         // 定义数据分隔线
         String BOUNDARY = "========7d4a6d158c9";
         // 服务器的域名
         URL url = new URL(domain+"/upload/UploadServlet");//通过form表单生成上传到服务器的绝对路径
         HttpURLConnection conn = (HttpURLConnection) url.openConnection();
         // 设置为POST情
         conn.setRequestMethod("POST");
         // 发送POST请求必须设置如下两行
         conn.setDoOutput(true);
         conn.setDoInput(true);
         conn.setUseCaches(false);
         // 设置请求头参数
         conn.setRequestProperty("connection", "Keep-Alive");
         conn.setRequestProperty("Charsert", "UTF-8");
         conn.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + BOUNDARY);
         OutputStream out = new DataOutputStream(conn.getOutputStream());
         // 上传文件
         String fileRealName = multipartFile.getOriginalFilename();//获得原始文件名;
         StringBuilder sb = new StringBuilder();
         sb.append(boundaryPrefix);
         sb.append(BOUNDARY);
         sb.append(newLine);
         // 文件参数,photo参数名可以随意修改
         sb.append("Content-Disposition: form-data;name="photo";filename="" + fileRealName + """ + newLine);
         sb.append("Content-Type:application/octet-stream");
         // 参数头设置完以后需要两个换行，然后才是参数内容
         sb.append(newLine);
         sb.append(newLine);
         // 将参数头的数据写入到输出流中
         out.write(sb.toString().getBytes());
         // 数据输入流,用于读取文件数据
         DataInputStream in = new DataInputStream(multipartFile.getInputStream());
         byte[] bufferOut = new byte[1024];
         int bytes = 0;
         // 每次读1KB数据,并且将文件数据写入到输出流中
         while ((bytes = in.read(bufferOut)) != -1) {
            out.write(bufferOut, 0, bytes);
         }
         // 最后添加换行
         out.write(newLine.getBytes());
         in.close();
         // 定义最后数据分隔线，即--加上BOUNDARY再加上--。
         byte[] end_data = (newLine + boundaryPrefix + BOUNDARY + boundaryPrefix + newLine).getBytes();
         // 写上结尾标识
         out.write(end_data);
         out.flush();
         out.close();
//          定义BufferedReader输入流来读取URL的响应
         BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));//POST请求upload服务
//对Json response进行解析
         JSONObject resultObj = JSON.parseObject(reader.readLine());
         JSONObject resultData= resultObj.getJSONObject("data");
         if(null == resultData)
            throw new ServiceException("源文件不存在");
         JSONArray data = resultData.getJSONArray("images");
         if(resultData.getJSONArray("images").size()!=0){
            data = resultData.getJSONArray("images");
         }else if(resultData.getJSONArray("videos").size()!=0){
            data = resultData.getJSONArray("videos");
         }else if(resultData.getJSONArray("audios").size()!=0){
            data = resultData.getJSONArray("audios");
         }else if(resultData.getJSONArray("others").size()!=0){
            data = resultData.getJSONArray("others");
         }

         if (data.size() > 0){
            JSONObject imageData = data.getJSONObject(0);
            newUrl = imageData.getString("oUrl");//"tUrl"
            System.out.println(" upload new Url =====>"+newUrl);
            return newUrl;//图片视频在服务器上的绝对路径，可以将该路径上传到客户端，客户端可现实该视频和图片
         }

      } catch (Exception e) {
         System.out.println("发送POST请求出现异常！" + e);
         e.printStackTrace();
      }
      return newUrl;
   }

//uploadServlet form表单上传的类

@WebServlet("/upload/UploadServlet")
public class UploadServlet extends BaseServlet {
    private static final long serialVersionUID = 1L;

    public UploadServlet() {
        super();
    }

    @Override
    protected JMessage hander(HttpServletRequest request, HttpServletResponse response) {
        long start = System.currentTimeMillis();
        DiskFileItemFactory factory = new DiskFileItemFactory(1000 * 1024 * 1024, new File(getSystemConfig().getuTemp()));
        ServletFileUpload fileUpload = new ServletFileUpload(factory);
        List<FileItem> multipart = null;

        JMessage jMessage = null;
        int totalCount = 0;
        // int uploadFlag = 0;
        long userId = 0;
        double validTime = 0;
        try {
            multipart = fileUpload.parseRequest(request);
            for (FileItem item : multipart) {
                if (item.isFormField()) {
                    if ("validTime".equals(item.getFieldName())) {
                        try {
                            validTime = Double.valueOf(item.getString());
                        } catch (NumberFormatException e) {
                            validTime = new Double(-1);
                        }
                    }
                    if ("userId".equals(item.getFieldName())) {
                        userId = Long.parseLong(item.getString());
                    }
                } else {
                    if (item.getSize() > 0) {
                        totalCount++;
                    }
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        if (null == multipart) {
            jMessage = new JMessage(1020101, "表单解析失败");
        }
        // else if (0 == uploadFlag) {
        // jMessage = new JMessage(1010101, "缺少上传标记");
        // }
        else if (0 == totalCount) {
            jMessage = new JMessage(1010101, "缺少上传文件");
        }
        if (null != jMessage)
            return jMessage;
        if (1 == getSystemConfig().getIsOpenfastDFS()) {
            jMessage = fastDFSHander(multipart, validTime);
        } else
            jMessage = defHander(multipart, userId, validTime);

        int successCount = jMessage.getIntValue("success");
        jMessage.put("total", totalCount);
        jMessage.put("failure", totalCount - successCount);
        jMessage.put("time", System.currentTimeMillis() - start);

        return jMessage;
    }

    protected JMessage fastDFSHander(List<FileItem> multipart, double validTime) {
        JMessage message = null;
        int successCount = 0;
        List<UploadItem> images = Lists.newArrayList();
        List<UploadItem> audios = Lists.newArrayList();
        List<UploadItem> videos = Lists.newArrayList();
        List<UploadItem> others = Lists.newArrayList();
        String oUrl = null;
        String tUrl = null;
        for (FileItem item : multipart) {
            UploadItem uploadItem;
            if (item.isFormField() || item.getSize() < 1)
                continue;
            String fileName = item.getName();
            String formatName = getFormatName(fileName);

            FileType fileType = getFileType(formatName);
            String path = uploadToFastDFS(item, validTime);
            if (StringUtils.isEmpty(path))
                continue;
            oUrl = path;
            tUrl = path;
            successCount++;
            if (FileType.Image == fileType) {//图片
                try {
                    uploadItem = new UploadItem(fileName, oUrl, tUrl, (byte) 1, null);
                } catch (Exception e) {
                    e.printStackTrace();
                    uploadItem = new UploadItem(fileName, null, (byte) 0, e.getMessage());
                }
                images.add(uploadItem);
            } else {//其他
                try {
                    uploadItem = new UploadItem(fileName, oUrl, tUrl, (byte) 1, null);
                    if ((fileName.indexOf(".amr") != -1) && 1 == getSystemConfig().getAmr2mp3()) {
                        /*File __source = new File(oFile.getPath());
                        File __target = new File(oFile.getPath().replaceAll(".amr", ".mp3"));
                        Amr2mp3.changeToMp3(__source.getPath(), __target.getPath());
                        successCount++;
                        oUrl= SystemConfig.getUrl(__target);
                        uploadItem = new UploadItem(__target.getName(),oUrl, (byte) 1, null);*/
                    } else {
                        /*successCount++;
                        oUrl= SystemConfig.getUrl(oFile);
                        uploadItem = new UploadItem(oFileName, oUrl, (byte) 1, null);*/
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                    uploadItem = new UploadItem(fileName, null, (byte) 0, e.getMessage());
                }
                if (FileType.Audio == fileType)
                    audios.add(uploadItem);
                else if (FileType.Video == fileType)
                    videos.add(uploadItem);
                else
                    others.add(uploadItem);
            }
        }

        Map<String, Object> data = new HashMap<String, Object>();
        data.put("images", images);
        data.put("audios", audios);
        data.put("videos", videos);
        data.put("others", others);


        message = new JMessage(1, null, data);

        message.put("success", successCount);

        return message;
    }

    protected JMessage defHander(List<FileItem> multipart, long userId, double validTime) {
        JMessage jMessage = null;
        int successCount = 0;
        String oUrl = null;
        String tUrl = null;
        List<UploadItem> images = Lists.newArrayList();
        List<UploadItem> audios = Lists.newArrayList();
        List<UploadItem> videos = Lists.newArrayList();
        List<UploadItem> others = Lists.newArrayList();

        for (FileItem item : multipart) {
            UploadItem uploadItem;
            if (item.isFormField() || item.getSize() < 1)
                continue;
            String oFileName = item.getName();
            String formatName = ConfigUtils.getFormatName(oFileName);
            String newFileName = ConfigUtils.getName(oFileName);
            String fileName = null;
            if (!StringUtils.isEmpty(newFileName) && !newFileName.equals(oFileName)) {
                fileName = 32 == newFileName.length() ? oFileName
                        : Joiner.on("").join(UUID.randomUUID().toString().replace("-", ""), ".", formatName);
            } else {
                fileName = oFileName;
            }
         /*String fileName = 32 == ConfigUtils.getName(oFileName).length() ? oFileName : Joiner.on("").join(UUID.randomUUID().toString().replace("-", ""), ".", formatName);*/
            FileType fileType = getFileType(formatName);
            File[] uploadPath = ConfigUtils.getUploadPath(userId, fileType);
            if (FileType.Image == fileType) {//图片
                File oFile = new File(uploadPath[0], fileName);
                File tFile = new File(uploadPath[1], fileName);
                try {
                    FileUtils.transfer(item.getInputStream(), oFile, tFile, formatName);

                    successCount++;
                    oUrl = getUrl(oFile);
                    tUrl = getUrl(tFile);
                    ResourcesDBUtils.saveFileUrl(1, oUrl, validTime);
                    ResourcesDBUtils.saveFileUrl(1, tUrl, validTime);
                    log("UploadServlet uploadEd " + oUrl);
                    log("UploadServlet uploadEd " + tUrl);
                    uploadItem = new UploadItem(oFileName, oUrl, tUrl, (byte) 1, null);
                } catch (Exception e) {
                    e.printStackTrace();
                    uploadItem = new UploadItem(oFileName, null, (byte) 0, e.getMessage());
                }
                images.add(uploadItem);
            } else {//其他
                File oFile = new File(uploadPath[0], fileName);
                try {
                    FileUtils.transfer(item.getInputStream(), oFile);
                    if ((fileName.indexOf(".amr") != -1) && 1 == getSystemConfig().getAmr2mp3()) {
                        File __source = new File(oFile.getPath());
                        File __target = new File(oFile.getPath().replaceAll(".amr", ".mp3"));
                        Amr2mp3.changeToMp3(__source.getPath(), __target.getPath());
                        successCount++;
                        oUrl = getUrl(__target);
                        uploadItem = new UploadItem(__target.getName(), oUrl, (byte) 1, null);
                    } else {
                        successCount++;
                        oUrl = getUrl(oFile);
                        uploadItem = new UploadItem(oFileName, oUrl, (byte) 1, null);
                    }
                    ResourcesDBUtils.saveFileUrl(1, oUrl, -1);
                    log("UploadServlet uploadEd " + oUrl);
                } catch (Exception e) {
                    e.printStackTrace();
                    uploadItem = new UploadItem(oFileName, null, (byte) 0, e.getMessage());
                }
                if (FileType.Audio == fileType)
                    audios.add(uploadItem);
                else if (FileType.Video == fileType)
                    videos.add(uploadItem);
                else
                    others.add(uploadItem);
            }
        }

        Map<String, Object> data = new HashMap<String, Object>();
        data.put("images", images);
        data.put("audios", audios);
        data.put("videos", videos);
        data.put("others", others);
        jMessage = new JMessage(1, null, data);

        jMessage.put("success", successCount);
        return jMessage;

    }
}