1.1 项目背景

对于超大文件上传我们可能遇到以下问题
• 大文件直接上传，占用过多内存，可能导致内存溢出甚至系统崩溃
• 受网络环境影响，可能导致传输中断，只能重新传输
• 传输时间长，用户无法知道传输进度，用户体验不佳

1.2 项目目标

对于上述问题，我们需要对文件做分片传输。分片传输就是把文件分割成许多较小的文件，然后分多次上传，最后再完成合并。

受网络环境影响，我们还要实现断点续传，以节省传输时间和资源。断点续传就是已经上传或者下载过的文件分片不再传输。

对于已经上传过的文件，可以不再上传，实现秒传。秒传就是根据文件的唯一标识，确认是否需要上传。
实现多任务上传或下载。多任务就是同时多个文件上传或下载。

2.1 业务流程

用户上传文件的流程图如图1所示，用户首先选择要上传的文件，上传过程中可以选择暂停或继续上传。

用户上传文件的流程图如图2所示，用户首先可以浏览可以下载的文件列表，然后点击下载，下载过程中可以选择暂停或继续下载

2.2 系统用例

系统用例图如图3所示，用户可以上传文件，在文件上传过程中可以查看文件的上传进度和速度，也可以暂停或开始上传；用户可以查看已经上传过的，也就是可以下载的文件列表；用户可以下载文件，在下载过程中可以查看文件下载的速度和进度，用户可以暂停或开始下载。

2.3 系统总体功能

系统总体功能图如图4所示，分为上传和下载。上传包括秒传，分片上传，断点续传，多任务。下载包括分片下载，断点续传，多任务。

3.1 技术选型

后端：
• 语言：Java8
• 框架：SpringBoot2.6
• 开发工具：Idea 2021
前端：
• 语言：Html5、css3、JavaScript
• 框架：Vue3
• 开发工具：Vscode、Edge
数据库：
• mysql8

4.1 文件上传模块

文件上传模块的流程图如图6所示，顺序图如图7所示
首先前端读取文件生成文件的唯一标识MD5,这里采用常用的MD5生成框架：spark-md5.js。对于大文件一次性读取比较慢，而且容易造成浏览器崩溃，因此这里采用分片读取的方式计算MD5。

然后向服务器发送请求，查看该文件时候已经上传，如果已经上传，就提示用户已经秒传。
如果数据库中没有记录该文件，就表示该文件没有上传或没有上传完成，那么服务器就查询并返回记录的chunk分片列表。

async 和 await配可以实现等待异步函数计算完成

//计算文件的md5值
function computeMd5(file, uploadFile) {
  return new Promise((resolve, reject) => {
    //分片读取并计算md5

    const chunkTotal = 100; //分片数
    const chunkSize = Math.ceil(file.size / chunkTotal);
    const fileReader = new FileReader();
    const md5 = new SparkMD5();
    let index = 0;
    const loadFile = (uploadFile) => {
      uploadFile.parsePercentage.value = parseInt((index / file.size) * 100);
      const slice = file.slice(index, index + chunkSize);
      
      fileReader.readAsBinaryString(slice);
    };
    loadFile(uploadFile);
    fileReader.onload = (e) => {
      md5.appendBinary(e.target.result);
      if (index  file.size) {
        index += chunkSize;
        loadFile(uploadFile);
      } else {
        // md5.end() 就是文件md5码
        resolve(md5.end());
      }
    };
  });
}
//检查文件是否存在
function checkFile(md5) {
  return request({
    url: "/check",
    method: "get",
    params: {
      md5: md5,
    },
  });
}
//文件上传之前,el-upload自动触发
async function beforeUpload(file) {
  console.log("2.上传文件之前");


  var uploadFile = {};
  uploadFile.name = file.name;
  uploadFile.size = file.size;
  uploadFile.parsePercentage = ref(0);
  uploadFile.uploadPercentage = ref(0);
  uploadFile.uploadSpeed = "0 M/s";
  uploadFile.chunkList = null;
  uploadFile.file = file;
  uploadFile.uploadingStop = false;
  uploadFileList.value.push(uploadFile);

  var md5 = await computeMd5(file, uploadFile);//async 和 await配可以实现等待异步函数计算完成
  uploadFile.md5 = md5;

  var res = await checkFile(md5);  //上传服务器检查，以确认是否秒传
  var data = res.data.data;

  if (!data.isUploaded) {
    uploadFile.chunkList = data.chunkList;
    uploadFile.needUpload = true;
  } else {
    uploadFile.needUpload = false;
    uploadFile.uploadPercentage.value = 100;

    console.log("文件已秒传");
    ElMessage({
      showClose: true,
      message: "文件已秒传",
      type: "warning",
    });
  }


}

前端分片请求文件，如果分片编号被包含在分片列表内，就标识该分片已经上传，跳过；反之，表示还未上传，那么前端通过file的slice方法分割文件，向服务端传递。同时在页面上显示上传进度和速度。

服务端，收到前端的分片文件后，通过Java的RandomAccess类（随机读写类），从文件的指定位置，写入指定字节，并记录chunk到数据库，如果是最后一个分片再记录file到数据库。

图6 文件上传流程图

图7 文件上传顺序图

前端代码

template>
  div class="main">
    
    el-upload
      action="#"
      :http-request="upload"
      :before-upload="beforeUpload"
      :show-file-list="false"
    >
      el-button type="primary">选择上传文件el-button>
    el-upload>

    el-divider content-position="left">上传列表el-divider>
    
    div class="uploading" v-for="uploadFile in uploadFileList">
      span class="fileName">{{ uploadFile.name }}span>
      span class="fileSize">{{ formatSize(uploadFile.size) }}span>

      div class="parse">
        span>解析进度： span>
        el-progress
          :text-inside="true"
          :stroke-width="16"
          :percentage="uploadFile.parsePercentage"
        >
        el-progress>
      div>
      div class="progress">
        span>上传进度：span>

        el-progress
          :text-inside="true"
          :stroke-width="16"
          :percentage="uploadFile.uploadPercentage"
        >
        el-progress>
        span
          v-if="
            (uploadFile.uploadPercentage > 0) &
            (uploadFile.uploadPercentage "
        >
          span class="uploadSpeed">{{ uploadFile.uploadSpeed }}span>

          el-button circle link @click="changeUploadingStop(uploadFile)">
            el-icon size="20" v-if="uploadFile.uploadingStop == false"
              >VideoPause
            />el-icon>
            el-icon size="20" v-else>VideoPlay />el-icon>
          el-button>
        span>
      div>
    div>
  div>
template>

script setup>
import emitter from "../utils/eventBus.js";
import { ElMessage } from "element-plus";
import SparkMD5 from "spark-md5";
import { VideoPause, VideoPlay } from "@element-plus/icons-vue";
import { ref, reactive, getCurrentInstance, nextTick } from "vue";
const { appContext } = getCurrentInstance();
const request = appContext.config.globalProperties.request;
var uploadFileList = ref([]);

//换算文件的大小单位
function formatSize(size) {
  //size的单位大小k

  var unit;
  var units = [" B", " K", " M", " G"];
  var pointLength = 2;
  while ((unit = units.shift()) && size > 1024) {
    size = size / 1024;
  }
  return (
    (unit === "B"
      ? size
      : size.toFixed(pointLength === undefined ? 2 : pointLength)) + unit
  );
}
//计算文件的md5值
function computeMd5(file, uploadFile) {
  return new Promise((resolve, reject) => {
    //分片读取并计算md5

    const chunkTotal = 100; //分片数
    const chunkSize = Math.ceil(file.size / chunkTotal);
    const fileReader = new FileReader();
    const md5 = new SparkMD5();
    let index = 0;
    const loadFile = (uploadFile) => {
      uploadFile.parsePercentage.value = parseInt((index / file.size) * 100);
      const slice = file.slice(index, index + chunkSize);
      
      fileReader.readAsBinaryString(slice);
    };
    loadFile(uploadFile);
    fileReader.onload = (e) => {
      md5.appendBinary(e.target.result);
      if (index  file.size) {
        index += chunkSize;
        loadFile(uploadFile);
      } else {
        // md5.end() 就是文件md5码
        resolve(md5.end());
      }
    };
  });
}
//检查文件是否存在
function checkFile(md5) {
  return request({
    url: "/check",
    method: "get",
    params: {
      md5: md5,
    },
  });
}
//文件上传之前,el-upload自动触发
async function beforeUpload(file) {
  console.log("2.上传文件之前");


  var uploadFile = {};
  uploadFile.name = file.name;
  uploadFile.size = file.size;
  uploadFile.parsePercentage = ref(0);
  uploadFile.uploadPercentage = ref(0);
  uploadFile.uploadSpeed = "0 M/s";
  uploadFile.chunkList = null;
  uploadFile.file = file;
  uploadFile.uploadingStop = false;
  uploadFileList.value.push(uploadFile);

  var md5 = await computeMd5(file, uploadFile);//async 和 await配可以实现等待异步函数计算完成
  uploadFile.md5 = md5;

  var res = await checkFile(md5);  //上传服务器检查，以确认是否秒传
  var data = res.data.data;

  if (!data.isUploaded) {
    uploadFile.chunkList = data.chunkList;
    uploadFile.needUpload = true;
  } else {
    uploadFile.needUpload = false;
    uploadFile.uploadPercentage.value = 100;

    console.log("文件已秒传");
    ElMessage({
      showClose: true,
      message: "文件已秒传",
      type: "warning",
    });
  }


}
//点击暂停或开始上传
function changeUploadingStop(uploadFile) {
 
  uploadFile.uploadingStop = !uploadFile.uploadingStop;
  if (!uploadFile.uploadingStop) {
    uploadChunk(uploadFile.file, 1, uploadFile);
  }
}
//上传文件,替换el-upload的action
function upload(xhrData) {
  var uploadFile = null;
 

  for (var i = 0; i  uploadFileList.value.length; i++) {
  
    if (
      (xhrData.file.name == uploadFileList.value[i].name) &
      (xhrData.file.size == uploadFileList.value[i].size)
    ) {
      uploadFile = uploadFileList.value[i];

      break;
    }
  }


  if (uploadFile.needUpload) {
    console.log("3.上传文件");

    // 分片上传文件
    // 确定分片的大小
    uploadChunk(xhrData.file, 1, uploadFile);
  }
}
//上传文件分片
function uploadChunk(file, index, uploadFile) {
  var chunkSize = 1024 * 1024 * 10; //10mb
  var chunkTotal = Math.ceil(file.size / chunkSize);
  if (index  chunkTotal) {
    // 根据是否暂停，确定是否继续上传

    // console.log("4.上传分片");

    var startTime = new Date().valueOf();


    var exit = uploadFile.chunkList.includes(index);
    // console.log("是否存在",exit);


    if (!exit) {
      //    console.log("3.3上传文件",uploadingStop);
      if (!uploadFile.uploadingStop) {
        // 分片上传，同时计算进度条和上传速度
        // 已经上传的不在上传、
        // 上传完成后提示，上传成功
        // console.log("上传分片1",index);
        var form = new FormData();
        var start = (index - 1) * chunkSize;
        let end =
          index * chunkSize >= file.size ? file.size : index * chunkSize;
        let chunk = file.slice(start, end);
        //  downloadBlob(chunk,file)
        //  console.log("chunk",chunk);

        form.append("chunk", chunk);
        form.append("index", index);
        form.append("chunkTotal", chunkTotal);
        form.append("chunkSize", chunkSize);
        form.append("md5", uploadFile.md5);
        form.append("fileSize", file.size);
        form.append("fileName", file.name);
        // console.log("上传分片", index);

        request({
          url: "/upload/chunk",
          method: "post",
          data: form,
        }).then((res) => {
          var endTime = new Date().valueOf();
          var timeDif = (endTime - startTime) / 1000;
          // console.log("上传文件大小",formatSize(chunkSize));
          // console.log("耗时",timeDif);
          // console.log("then",index);

          // uploadSpeed = (chunkSize/(1024*1024))  / timeDif +" M / s"

          uploadFile.uploadSpeed = (10 / timeDif).toFixed(1) + " M/s";
          // console.log(res.data.data);
          //  console.log("f2",uploadFile);
          uploadFile.chunkList.push(index);
          //  console.log("f3",uploadFile);

          uploadFile.uploadPercentage = parseInt(
            (uploadFile.chunkList.length / chunkTotal) * 100
          );
          // console.log("上传进度",uploadFile.uploadPercentage);

          if (index == chunkTotal) {
            emitter.emit("reloadFileList");
          }

          uploadChunk(file, index + 1, uploadFile);
        });
      }
    } else {
      uploadFile.uploadPercentage = parseInt(
        (uploadFile.chunkList.length / chunkTotal) * 100
      );

      uploadChunk(file, index + 1, uploadFile);
    }
    // }
  }
}
script>

style  scoped>
.main {
  margin-top: 40px;
  margin-bottom: 40px;
}
.uploading {
  padding-top: 27px;
}
.progress {
  /* width: 700px; */
  display: flex;
}
.uploading .parse {
  display: flex;
}
.parse .el-progress {
  /* font-size: 18px; */
  width: 590px;
}
.progress .el-progress {
  /* font-size: 18px; */
  width: 590px;
}
.uploading .fileName {
  font-size: 17px;
  margin-right: 40px;
  margin-left: 80px;

  /* width: 80px; */
}
.uploading .fileSize {
  font-size: 17px;

  /* width: 80px; */
}

.progress .uploadSpeed {
  font-size: 17px;
  margin-left: 5px;
  padding-left: 5px;
  padding-right: 10px;
}
style>

后端代码

package com.cugb.bigfileupload.controller;

import com.cugb.bigfileupload.bean.FilePO;
import com.cugb.bigfileupload.bean.Result;
import com.cugb.bigfileupload.servie.ChunkService;
import com.cugb.bigfileupload.servie.FileService;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.multipart.MultipartFile;

import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Objects;

@RestController
@CrossOrigin
public class FileController {
    Logger logger = LoggerFactory.getLogger(getClass());

    @Value("${file.path}")
    private String filePath;

    @Autowired
    private FileService fileService;
    @Autowired
    private ChunkService chunkService;
    @GetMapping("/check")
    public Result checkFile(@RequestParam("md5") String md5){
        logger.info("检查MD5:"+md5);
        //首先检查是否有完整的文件
        Boolean isUploaded = fileService.selectFileByMd5(md5);
        MapString, Object> data = new HashMap>();
        data.put("isUploaded",isUploaded);
        //如果有，就返回秒传
        if(isUploaded){
            return new Result(201,"文件已经秒传",data);
        }

        //如果没有，就查找分片信息，并返回给前端
        ListInteger> chunkList = chunkService.selectChunkListByMd5(md5);
        data.put("chunkList",chunkList);

        return  new Result(201,"",data);
    }

    @PostMapping("/upload/chunk")
    public Result uploadChunk(@RequestParam("chunk") MultipartFile chunk,
                              @RequestParam("md5") String md5,
                              @RequestParam("index") Integer index,
                              @RequestParam("chunkTotal")Integer chunkTotal,
                              @RequestParam("fileSize")Long fileSize,
                              @RequestParam("fileName")String fileName,
                              @RequestParam("chunkSize")Long chunkSize
    ){


        String[] splits = fileName.split("\.");
        String type = splits[splits.length-1];
        String resultFileName = filePath+md5+"."+type;

        chunkService.saveChunk(chunk,md5,index,chunkSize,resultFileName);
        logger.info("上传分片："+index +" ,"+chunkTotal+","+fileName+","+resultFileName);
        if(Objects.equals(index, chunkTotal)){
            FilePO filePO = new FilePO(fileName, md5, fileSize);
            fileService.addFile(filePO);
            chunkService.deleteChunkByMd5(md5);
            return  new Result(200,"文件上传成功",index);
        }else{
            return new Result(201,"分片上传成功",index);
        }

    }

    @GetMapping("/fileList")
    public Result getFileList(){
        logger.info("查询文件列表");
        ListFilePO> fileList = fileService.selectFileList();

        return  new Result(201,"文件列表查询成功",fileList);
    }
}

4.2 文件下载模块

文件下载的流程图如图8所示，顺序图如图9所示
文件下载是首先，前端向后端发送分片下载的请求，请求的responseType设为blob(Binary large Object) ,然后后端通过RandomAccess类读取指定字节的内容，再写入到响应的文件流中。

浏览器前端的请求的分片数据，会暂时保存在“C:Users用户名AppDataLocalMicrosoftEdgeUser DataDefaultblob_storage”中，（请确保c盘有足够的空间），当所有分片下载完成，会合并成一个大文件（很快），分片不是放在内存中，所以不用担心文件太大是不是不行。
，
刷新浏览器，也会删除已经下载好的分片

当前端请求了所有的文件分片之后，再把所有的blob合并成一个blob

if (index == chunkTotal) {
            var resBlob = new Blob(file.blobList, {
              type: "application/octet-stream",
            });
            // console.log("resb", resBlob);

            let url = window.URL.createObjectURL(resBlob); // 将获取的文件转化为blob格式
            let a = document.createElement("a"); // 此处向下是打开一个储存位置
            a.style.display = "none";
            a.href = url;
            // 下面两行是自己项目需要的处理，总之就是得到下载的文件名（加后缀）即可

            var fileName = file.name;

            a.setAttribute("download", fileName);
            document.body.appendChild(a);
            a.click(); //点击下载
            document.body.removeChild(a); // 下载完成移除元素
            window.URL.revokeObjectURL(url); // 释放掉blob对象
          }

图9文件上传顺序图

前端代码

template>
  div class="main">
    div class="fileList">
      div class="title">
        文件列表
        
      div>

      el-table :data="fileList" border style="width: 360px">
        el-table-column prop="name" label="文件名" width="150">
        el-table-column>

        el-table-column prop="size" label="文件大小" width="110">
          template #default="scope">
            {{ formatSize(scope.row) }}
          template>
        el-table-column>
        el-table-column prop="" label="操作" width="100">
          template #default="scope">
            el-button
              size="small"
              type="primary"
              @click="downloadFile(scope.row)"
              >下载el-button
            >
          template>
        el-table-column>
      el-table>
    div>

    div class="downloadList">
      el-divider content-position="left">下载列表el-divider>

      div v-for="file in downloadingFileList">
        div class="downloading">
          span class="fileName">{{ file.name }}span>
          span class="fileSize">{{ formatSize(file) }}span>
          span class="downloadSpeed">{{ file.downloadSpeed }}span>

          div class="progress">
            span>下载进度：span>

            el-progress
              :text-inside="true"
              :stroke-width="16"
              :percentage="file.downloadPersentage"
            >
            el-progress>

            el-button circle link @click="changeDownloadStop(file)">
              el-icon size="20" v-if="file.downloadingStop == false"
                >VideoPause
              />el-icon>
              el-icon size="20" v-else>VideoPlay />el-icon>
            el-button>
          div>
        div>
      div>
    div>
  div>
template>

script setup>
import axios from "axios";
import { ref, reactive, getCurrentInstance } from "vue";
import emitter from "../utils/eventBus.js";
import { VideoPause, VideoPlay } from "@element-plus/icons-vue";
const { appContext } = getCurrentInstance();
const request = appContext.config.globalProperties.request;
var fileList = reactive([]);
var downloadingFileList = ref([]);
//上传文件之后，重新加载文件列表
emitter.on("reloadFileList", () => {
  load();
});
function load() {
  fileList.length = 0;
  request({
    url: "/fileList",
    method: "get",
  }).then((res) => {
    // console.log("res", res.data.data);
    fileList.push(...res.data.data);
  });
}
load();

//换算文件的大小单位
function formatSize(file) {
  //console.log("size",file.size);
  var size = file.size;
  var unit;
  var units = [" B", " K", " M", " G"];
  var pointLength = 2;
  while ((unit = units.shift()) && size > 1024) {
    size = size / 1024;
  }
  return (
    (unit === "B"
      ? size
      : size.toFixed(pointLength === undefined ? 2 : pointLength)) + unit
  );
}
//点击暂停下载
function changeDownloadStop(file) {
  file.downloadingStop = !file.downloadingStop;
  if (!file.downloadingStop) {
    console.log("开始。。");

    downloadChunk(1, file);
  }
}
//点击下载文件
function downloadFile(file) {
  // console.log("下载", file);
  file.downloadingStop = false;
  file.downloadSpeed = "0 M/s";
  file.downloadPersentage = 0;
  file.blobList = [];
  file.chunkList = [];
  downloadingFileList.value.push(file);

  downloadChunk(1, file);
}
//点击下载文件分片
function downloadChunk(index, file) {
  var chunkSize = 1024 * 1024 * 5;
  var chunkTotal = Math.ceil(file.size / chunkSize);

  if (index  chunkTotal) {
    // console.log("下载进度",index);
    var exit = file.chunkList.includes(index);
    console.log("存在", exit);

    if (!exit) {
      if (!file.downloadingStop) {
        var formData = new FormData();
        formData.append("fileName", file.name);
        formData.append("md5", file.md5);
        formData.append("chunkSize", chunkSize);
        formData.append("index", index);
        formData.append("chunkTotal", chunkTotal);
        if (index * chunkSize >= file.size) {
          chunkSize = file.size - (index - 1) * chunkSize;
          formData.set("chunkSize", chunkSize);
        }

        var startTime = new Date().valueOf();

        axios({
          url: "http://localhost:9001/download",
          method: "post",
          data: formData,
          responseType: "blob",
          timeout: 50000,
        }).then((res) => {
          file.chunkList.push(index);
          var endTime = new Date().valueOf();
          var timeDif = (endTime - startTime) / 1000;
          file.downloadSpeed = (5 / timeDif).toFixed(1) + " M/s";
          //todo
          file.downloadPersentage = parseInt((index / chunkTotal) * 100);
          // var chunk = res.data.data.chunk
          // const blob = new Blob([res.data]);
          const blob = res.data;

          file.blobList.push(blob);
          // console.log("res", blobList);
          if (index == chunkTotal) {
            var resBlob = new Blob(file.blobList, {
              type: "application/octet-stream",
            });
            // console.log("resb", resBlob);

            let url = window.URL.createObjectURL(resBlob); // 将获取的文件转化为blob格式
            let a = document.createElement("a"); // 此处向下是打开一个储存位置
            a.style.display = "none";
            a.href = url;
            // 下面两行是自己项目需要的处理，总之就是得到下载的文件名（加后缀）即可

            var fileName = file.name;

            a.setAttribute("download", fileName);
            document.body.appendChild(a);
            a.click(); //点击下载
            document.body.removeChild(a); // 下载完成移除元素
            window.URL.revokeObjectURL(url); // 释放掉blob对象
          }

          downloadChunk(index + 1, file);
        });
      }
    } else {
      file.downloadPersentage = parseInt((index / chunkTotal) * 100);
      downloadChunk(index + 1, file);
    }
  }
}
script>

style  scoped>
.main {
  display: flex;
}
.fileList {
  width: 400px;
}
.downloadList {
  width: 450px;
}
.title {
  margin-top: 5px;
  margin-bottom: 5px;
}
.downloading {
  margin-top: 10px;
}
.downloading .fileName {
  margin-left: 76px;
  margin-right: 30px;
}
.downloading .fileSize {
  /* margin-left: 70px; */
  margin-right: 30px;
}
.downloading .progress {
  display: flex;
}
.progress .el-progress {
  /* font-size: 18px; */
  width: 310px;
}
style>

后端代码

package com.cugb.bigfileupload.controller;

import com.cugb.bigfileupload.servie.ChunkService;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.*;

import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.IOException;
import java.util.Objects;

@Controller
@CrossOrigin
public class DownLoadController {
    Logger logger = LoggerFactory.getLogger(getClass());

    @Value("${file.path}")
    private String filePath;

    @Autowired
    private ChunkService chunkService;
    @PostMapping("/download")
    public void download(@RequestParam("md5") String md5,
                           @RequestParam("fileName") String fileName,
                           @RequestParam("chunkSize") Integer chunkSize,
                         @RequestParam("chunkTotal") Integer chunkTotal,
                           @RequestParam("index")Integer index,
                         HttpServletResponse response) {
        String[] splits = fileName.split("\.");
        String type = splits[splits.length - 1];
        String resultFileName = filePath + md5 + "." + type;

        File resultFile = new File(resultFileName);

        long offset = (long) chunkSize * (index - 1);
        if(Objects.equals(index, chunkTotal)){
            offset = resultFile.length() -chunkSize;
        }
        byte[] chunk = chunkService.getChunk(index, chunkSize, resultFileName,offset);


        logger.info("下载文件分片" + resultFileName + "," + index + "," + chunkSize + "," + chunk.length+","+offset);
//        response.addHeader("Access-Control-Allow-Origin","Content-Disposition");
        response.addHeader("Content-Disposition", "attachment;filename=" + fileName);
        response.addHeader("Content-Length", "" + (chunk.length));
        response.setHeader("filename", fileName);


        response.setContentType("application/octet-stream");
        ServletOutputStream out = null;
        try {
            out = response.getOutputStream();
            out.write(chunk);
            out.flush();
            out.close();
        } catch (IOException e) {
            e.printStackTrace();
        }


    }

}