SpringBoot+Vue实现大文件分块上传

小咪咪 2024-03-22 19:37 87阅读 0赞

## SpringBoot+Vue实现大文件分块上传 ##

## 1. 项目背景 ##

由于用户需求，需要上传大量图片，只能通过上传压缩包的形式上传，可是压缩包过大时，又会出现上传超时的情况，故需要将压缩包分块上传，然后解压缩图片、若图片过大则再对图片进行压缩。

## 2. 分块上传 ##

分块上传我在用的时候发现有两种：第一种：分块合并接口全由后端接口生成；第二种：前端分块，后端上传  
开始用的第一种，结果发现生成的文件没有内容，应该是向文件内写的方法有问题；所以又用的第二种；

### 2.1. 前端分页 ###

js文件：

import http from './index'
    
    export const white = (data) => http({
        
        url: '/api/file/upload',
        method: 'post',
        data
    })

页面：

<template>
        <div>
          <el-form ref="editForm" :model="formFileds">
            <el-row :gutter="24">
     
              <el-col :span="12">
                <el-form-item>
                  <el-input></el-input>
                </el-form-item>
              </el-col>
     
              <el-col :span="12">
                <el-form-item>
                  <el-button type="primary">
                    查询
                  </el-button>
     
                  <el-button type="primary" @click="add()">
                    增加
                  </el-button>
     
                </el-form-item>
              </el-col>
     
            </el-row>
     
     
          </el-form>
          <div>
                
                <input class="hidden" type="file" ref="file" v-on:change="uploadFile()" v-bind:id="inputId + '-input'">
    
            </div>
          
          <el-table ref="list" :data="tableData" style="width: 100%;margin-bottom: 5=1px;" border stripe highlight-current-row
            :default-sort="{ prop: 'sx', order: 'sx' }">
            
            <el-table-column fixed type="selection" width="45">
            </el-table-column>
            <el-table-column property="name" label="名称" align="center">
            </el-table-column>
            
            <el-table-column property="fbzt" label="发布状态" align="center">
              <template slot-scope="scope">
                <el-switch v-model="scope.row.fbzt" disabled></el-switch>
              </template>
            </el-table-column>
            <el-table-column property="sx" label="顺序" align="center">
            </el-table-column>
            <el-table-column fixed="right" label="操作" align="center">
              <template slot-scope="scope">
                
                <el-button circle icon="el-icon-edit-outline" type="primary" @click="Compile()" title="编辑" size="small">
                </el-button>
                <el-button circle icon="el-icon-delete" type="danger" title="删除" size="small"
                  @click="rowDel(scope.row.id)"></el-button>
              </template>
            </el-table-column>
          </el-table>
          
          <el-pagination :page-sizes="[10, 20, 30, 40, 100]" :page-size="10" :total="100"
            layout="total, sizes, prev, pager, next, jumper">
          </el-pagination>
     
          <Add v-if="isShowAddDialog" :isShowAddDialog="isShowAddDialog" @dialogClose="dialogClose"></Add>
          <Compile v-if="isShowComDialog" :isShowComDialog="isShowComDialog" @dialogClose="dialogClose"></Compile>
        </div>
      </template>
         
      <script>
      import Add from "./auctionProcessAdd.vue";
      import Compile from "./auctionProcesscomple.vue";
      import {
         getAllJmxz,deleteJmxz } from '@/api/systemAdministrator/auctionProcess';
      import {
        white} from '@/api/white'
      import axios from "axios";
     
      export default {
        
        name: "auctionProcess",
        components: {
        
          Add,
          Compile,
        },
        data() {
        
          return {
        
            editProps: '',
                text: '',
                inputId: '',
                hex_md5: '',
            formFileds: {
        
            },
            tableData: [
            {
        
            id: 0,
            name: '',
            fbzt: '',
            sx: 0,
            nr: "",
            bz: '',
            },
            ],
            pageSize: 10,
            total: 0,
            currentPage: 1,
            editProps: '',
            isShowAddDialog:false,
            isShowComDialog:false,
    
          }
        },
        methods: {
        
          /**
           * 点击【上传】
           */
            // selectFile () {
        
            //     let _this = this;
            //     $("#" + _this.inputId + "-input").trigger("click");
            // },
    
            /**
          * 上传文件
          */
          uploadFile () {
        
                let _this = this;
                // 1. 获取 input 中被选中的文件
                let file = _this.$refs.file.files[0];
    
    
                // 2. 生成文件标识，标识多次上传的是不是同一个文件
                //  let key = md5(file.name + file.size + file.type);
                // let key10 = parseInt(key, 16);
                // let key62 = Tool._10to62(key10);
                let time = Date.now();
                // console.log(time);
                let fileName = file.name;
                let temp = fileName.split('.');
                let key62 = time + '`' + temp[0];
                // console.log(key62);
                // 判断文件格式 （非必选，根据实际情况选择是否需要限制文件上传类型）
                // let suffixs = _this.suffixs;s
                
                let suffix = fileName.substring(fileName.lastIndexOf(".") + 1, fileName.length).toLowerCase();
                // if (!(!suffixs || JSON.stringify(suffixs) === "{}" || suffixs.length === 0)) {
        
                //     let validateSuffix = false;
                //     for (let s of suffixs) {
        
                //         if (s.toLocaleLowerCase() === suffix) {
        
                //             validateSuffix = true;
                //             break;
                //         }
                //     }
                //     if (!validateSuffix) {
        
                //         Toast.warning("文件格式不正确！只支持上传：" + suffixs.join(","));
                //         $("#" + _this0.inputId + "-input").val("");
                //         return;
                //     }
                // }
    
                // 3. 文件分片开始
                // 3.1 设置与计算分片必选参数
                let shardSize = 20 * 1024 * 1024; // 20M为一个分片
                let shardIndex = 1;   // 分片索引，1表示第1个分片
                let size = file.size; // 文件的总大小
                let shardTotal = Math.ceil(size / shardSize); // 总分片数
    
                //  3.2 拼接将要传递到参数， use 非必选，这里用来标识文件用途。
                let param = {
        
                    'shardIndex': shardIndex,
                    'shardSize': shardSize,
                    'shardTotal': shardTotal,
                    'use': _this.use,
                    'name': file.name,
                    'suffix': suffix,
                    'size': file.size,
                    'key': key62
                };
    
                //  3.3  传递分片参数，通过递归完成分片上传。
                _this.upload(param);
    
            },
    
            /**
       * 递归上传分片
       */
            upload (param) {
        
                let _this = this;
                let shardIndex = param.shardIndex;
                let shardTotal = param.shardTotal;
                let shardSize = param.shardSize;
                // 3.3.1 根据参数，获取文件分片
                let fileShard = _this.getFileShard(shardIndex, shardSize);
    
    
                // 3.3.2 将文件分片转为base64进行传输
                let fileReader = new FileReader();
                // 读取并转化 fileShard 为 base64
                fileReader.readAsDataURL(fileShard);
                //  readAsDataURL 读取后的回调，
                // 将 经过  base64 编码的  分片 整合到 param ，发送给后端，从而上传分片。
                fileReader.onload = function (e) {
        
                    let base64 = e.target.result;
                    param.shard = base64;
                    console.log('shard',param.shard)
                    //   Loading.show();
                    let params = new FormData();
                    params = param;
                    // params.append=(param);
                    // const params2 = JSON.stringify(params);
                    // console.log('params2',params2);
                    white(params).then((res) => {
        
                      console.log('!!!!!!!!!!!!!!!!!!!!!!!!!');
                      // console.log(params);
                    // axios.post('/api/file/upload', params).then((res)=> {
        
                        //   Loading.hide();
                        let resp = res.data;
                        // 上传结果
                        // 当前分片索引小于 分片总数，继续执行分派，反之 则表示全部上传成功。
                        if (shardIndex < shardTotal) {
        
                            // 上传下一个分片
                            param.shardIndex = param.shardIndex + 1;
                            // this.$message.warning('正在上传');
                            _this.upload(param);
                        } else {
        
                            // 文件上传成功后的回调
                            // _this.afterUpload(resp);
                            return ;
                            // this.$message.success('上传成功');
                        }
                        // $('#' + _this.inputId + '-input').val('');
                    });
                };
            },
            // axios.post('/api/file/upload',params).then((res)=>{
        
            // // white(param).then((res) => {
        
            // //   _this.$ajax.post( "localhost:8080/admin/upload", param).then((res)=> {
        
            //     //   Loading.hide();s
            //       let resp = res.data;
            //       // 上传结果
            //         // 当前分片索引小于 分片总数，继续执行分派，反之 则表示全部上传成功。
            //       if(shardIndex < shardTotal) {
        
            //         // 上传下一个分片
            //         param.shardIndex = param.shardIndex + 1;
            //         _this.upload(param);
            //       } else {
        
            //           // 文件上传成功后的回调
            //          _this.afterUpload(resp);
            //       }
            //       $("#" + _this.inputId + "-input").val("");
            //   });
    
    
            /**
            * 文件分片函数
            */
            getFileShard (shardIndex, shardSize) {
        
                let _this = this;
                let file = _this.$refs.file.files[0];
                let start = (shardIndex - 1) * shardSize; // 当前分片起始位置
                let end = Math.min(file.size, start + shardSize); // 当前分片结束位置
                let fileShard = file.slice(start, end); // 从文件中截取当前的分片数据
                return fileShard;
            },
          rowEdit(row) {
        
            if(row.fbzt == '已提交'){
        
              row.fbzt = 'true';
            }
            else{
        
              row.fbzt = 'false';
            }
            
            // //当前选中行
            this.rowDataS = row;
            console.log(1)
          },
          dialogClose() {
        
            this.isShowEditDialog = false;
            this.isShowAddDialog = false;
            this.isShowComDialog = false;
          },
          handleEdit(id) {
        
            this.$refs.editForm.validate(isValid => {
        
     
              if (!isValid) return;
     
              // 保存编辑后的数据
              Object.assign(this.tableData[id], this.formFileds);
              this.isShowEditDialog = false;
     
              // 考虑到可能编辑了日期-需要重新排序
              // ***注意：手动排序传参和表格的default-sort属性格式不太一样
              this.$refs.list.sort('date', 'descending');
     
              this.$message.success('编辑成功');
            });
          },
          getList(){
        
                this.param = 'pageno=' + this.currentPage + '&countonepage=' + this.pageSize;
                getAllJmxz(this.param).then((res) => {
        
                    if(res){
        
                        console.log(res.data);
                        console.log(res.msg);
                        this.tableData = res.data.list;
                        this.total = res.data.total;
                        for(let item of this.tableData){
        
                          if(item.fbzt == '已提交'){
        
                            item.fbzt = true;
                          }
                          else{
        
                            item.fbzt = false;
                          }
                        }
                    }
                })
            },
          add() {
        
            console.log("add");
            this.isShowAddDialog = true;
          },
          Compile() {
        
            console.log("Compile");
            this.isShowComDialog = true;
          },
          
          rowDel(id) {
        
            // this.formFileds = row;
            console.log(id);
                this.$confirm('确定要删除当前行吗？', '删除', {
        
                    comfirmButtonText: '确定',
                    cancelButtonText: '取消'
                }).then(() => {
        
                    deleteJmxz(id).then((res) => {
        
                        if(res){
        
                            console.log(res.data);
                            console.log(res.msg);
                            this.tableData.splice(id, 1);
                            this.$message.success('删除成功');
                            this.getList();
                        }
                    })
                });
          },
          // 选中当前行-当前行的复选框被勾选
          setCurRowChecked(row) {
        
     
            this.$refs.list.clearSelection();
            this.$refs.list.toggleRowSelection(row);
          },
        },
        mounted(){
        
            this.getList();
            // console.log(this.tableData);
            // console.log(new Date().toLocaleString());
        }
      }
      </script>
        
      <style scoped lang="less">
      .el-form {
        
        padding: 0 10px;
      }
     
      .el-date-editor {
        
        width: 100% !important;
      }
      </style>

### 2.2. 后端合并 ###

接收类：

package com.example.springboot.domain;
    
    import lombok.Data;
    
    import com.fasterxml.jackson.annotation.JsonFormat;
    import java.util.Date;
    @Data
    public class FileDto {
        
    
        /**
         * id
         */
        private String id;
    
        /**
         * 相对路径
         */
        private String path;
    
        /**
         * 文件名
         */
        private String name;
    
        /**
         * 后缀
         */
        private String suffix;
    
        /**
         * 大小|字节B
         */
        private Integer size;
    
        /**
         * 用途
         */
        private String use;
    
        /**
         * 创建时间
         */
        @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss", timezone = "GMT+8")
        private Date createdAt;
    
        /**
         * 修改时间
         */
        @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss", timezone = "GMT+8")
        private Date updatedAt;
    
        private Integer shardIndex;
    
        private Integer shardSize;
    
        private Integer shardTotal;
    
        private String key;
    
        /**
         * base64
         */
        private String shard;
    }

Controller：

package com.example.springboot.controller;
    
    
    
    import cn.hutool.core.img.ImgUtil;
    import cn.hutool.core.io.FileUtil;
    import cn.hutool.core.util.ZipUtil;
    import com.example.springboot.common.Base64ToMultipartFile;
    import com.example.springboot.common.FileViewer;
    import com.example.springboot.common.ReturnResult;
    import com.example.springboot.domain.FileDto;
    import net.coobird.thumbnailator.Thumbnails;
    import org.slf4j.Logger;
    import org.slf4j.LoggerFactory;
    import org.springframework.web.bind.annotation.*;
    import org.springframework.web.multipart.MultipartFile;
    
    
    import java.io.*;
    import java.text.SimpleDateFormat;
    import java.util.ArrayList;
    import java.util.Date;
    import java.util.List;
    
    @RequestMapping("/file")
    @RestController
    public class UploadController {
        
    
        private static final Logger LOG = LoggerFactory.getLogger(UploadController.class);
    
        private static final String storePath = "E:/usr/local/apps/pmxt-download/merge/";
    
    
        @PostMapping("/upload")
        public ReturnResult upload(@RequestBody FileDto fileDto) throws Exception {
        
            Date date = new Date();
            SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy/MM/dd/");
            String format = simpleDateFormat.format(date);
            LOG.info("日期信息："+format);
            String tem = storePath + format + fileDto.getName();
            File f1 = new File(tem);
            if (f1.exists()){
        
                f1.delete();
            }
            LOG.info("上传文件开始");
            String use = fileDto.getUse();
            String key = fileDto.getKey();
            String suffix = fileDto.getSuffix();
            String shardBase64 = fileDto.getShard();
            MultipartFile shard = Base64ToMultipartFile.base64ToMultipart(shardBase64);
    
            // 保存文件到本地
            String fullPath = storePath + format;
            if (!new File(fullPath).exists()){
        
                new File(fullPath).mkdirs();
            }
            String path = new StringBuffer(fullPath)
                    .append(key.split("`")[1])
                    .append(".")
                    .append(suffix)
                    .toString(); // course\6sfSqfOwzmik4A4icMYuUe.mp4
            System.out.println(path);
            String localPath = new StringBuffer(path)
                    .append(".")
                    .append(fileDto.getShardIndex())
                    .toString(); // course\6sfSqfOwzmik4A4icMYuUe.mp4.1
            System.out.println(localPath);
            File dest = new File(localPath);
            shard.transferTo(dest);
            System.out.println(dest.getAbsolutePath());
            LOG.info("保存文件记录开始");
            fileDto.setPath(path);
            // 合并分片
            if (fileDto.getShardIndex().equals(fileDto.getShardTotal())) {
        
                this.merge(fileDto);
            }
    //        ResponseDto<Object> responseDto = new ResponseDto<>();
    //        responseDto.setContent("http://127.0.0.1:8080/f/"+ format + key + "-" + fileName);
    //        return responseDto;
            return ReturnResult.buildSuccessResult("true");
        }
    
    
        public void merge(FileDto fileDto) throws Exception {
        
            LOG.info("合并分片开始");
            String path = fileDto.getPath(); //http://127.0.0.1:9000/file/f/course\6sfSqfOwzmik4A4icMYuUe.mp4
            Integer shardTotal = fileDto.getShardTotal();
            File newFile = new File(path);
            FileOutputStream outputStream = new FileOutputStream(newFile, true);//文件追加写入
            FileInputStream fileInputStream = null;//分片文件
            byte[] byt = new byte[10 * 1024 * 1024];
            int len;
            try {
        
                for (int i = 0; i < shardTotal; i++) {
        
                    // 读取第i个分片
                    fileInputStream = new FileInputStream(new File( path + "." + (i + 1))); //  course\6sfSqfOwzmik4A4icMYuUe.mp4.1
                    while ((len = fileInputStream.read(byt)) != -1) {
        
                        outputStream.write(byt, 0, len);
                    }
                }
            } catch (IOException e) {
        
                LOG.error("分片合并异常", e);
            } finally {
        
                try {
        
                    if (fileInputStream != null) {
        
                        fileInputStream.close();
                    }
                    outputStream.close();
                    LOG.info("IO流关闭");
                } catch (Exception e) {
        
                    LOG.error("IO流关闭", e);
                }
            }
            LOG.info("合并分片结束");
    
            // 删除分片
            LOG.info("删除分片开始");
            File file = null;
            String filePath = "";
            for (int i = 0; i < shardTotal; i++) {
        
                filePath =  path + "." + (i + 1);
                file = new File(filePath);
                System.gc();
                boolean result = file.delete();
                LOG.info("删除{}，{}", filePath, result ? "成功" : "失败");
            }
            LOG.info("删除分片结束");
        }
    
        @PostMapping("/unzip")
        public ReturnResult unzip(String path){
        
            return ReturnResult.buildSuccessResult(ZipUtil.unzip(path, "E:/usr/local/apps/pmxt-download/merge"));
        }
    
        @PostMapping("/selectBySize")
        public ReturnResult selectBySize(String path) {
        
            List<String> flist = FileViewer.getListFiles(path,true);
            for (String s : flist) {
        
                File file = new File(s);
                if (file.isDirectory()) {
        
                    return ReturnResult.buildFailureResult("文件不存在");
                } else {
        
                    if(file.length()>1048576*3){
        
                        ImgUtil.scale(
                                FileUtil.file(s),
                                FileUtil.file(s),
                                0.5f//缩放比例
                        );
    //                    try {
        
    //                        Thumbnails.of(s)
    //                                .scale(0.5f)
    //                                .outputQuality(0.5f)
    //                                .toFile(s);
    //                    } catch (IOException e) {
        
    //                        throw new RuntimeException(e);
    //                    }
                    }
                }
            }
            return ReturnResult.buildSuccessResult(true);
    
        }
    
    
    }

工具类：64位编码转文件

package com.example.springboot.common;
    
    import org.springframework.web.multipart.MultipartFile;
    import java.io.*;
    import java.util.Base64;
    
    public class Base64ToMultipartFile implements MultipartFile {
        
    
        private final byte[] imgContent;
        private final String header;
    
        public Base64ToMultipartFile(byte[] imgContent, String header) {
        
            this.imgContent = imgContent;
            this.header = header.split(";")[0];
        }
    
        @Override
        public String getName() {
        
            // TODO - implementation depends on your requirements
            return System.currentTimeMillis() + Math.random() + "." + header.split("/")[1];
        }
    
        @Override
        public String getOriginalFilename() {
        
            // TODO - implementation depends on your requirements
            return System.currentTimeMillis() + (int) Math.random() * 10000 + "." + header.split("/")[1];
        }
    
        @Override
        public String getContentType() {
        
            // TODO - implementation depends on your requirements
            return header.split(":")[1];
        }
    
        @Override
        public boolean isEmpty() {
        
            return imgContent == null || imgContent.length == 0;
        }
    
        @Override
        public long getSize() {
        
            return imgContent.length;
        }
    
        @Override
        public byte[] getBytes() throws IOException {
        
            return imgContent;
        }
    
        @Override
        public InputStream getInputStream() throws IOException {
        
            return new ByteArrayInputStream(imgContent);
        }
    
        @Override
        public void transferTo(File dest) throws IOException, IllegalStateException {
        
            new FileOutputStream(dest).write(imgContent);
        }
    
        public static MultipartFile base64ToMultipart(String base64) {
        
            System.out.println(base64);
            String[] baseStrs = base64.split(",");
    //            Encoder decoder = Base64.getEncoder();
            Base64.Decoder decoder = Base64.getDecoder();
            byte[] b;
            b = decoder.decode(baseStrs[1]);
    
            for(int i = 0; i < b.length; ++i) {
        
                if (b[i] < 0) {
        
                    b[i] += 256;
                }
            }
    
            return new Base64ToMultipartFile(b, baseStrs[0]);
        }
    }

返回类（若返回为字符串或者已有返回类，则这个类没用）：

package com.example.springboot.common;
    
    import lombok.Data;
    
    @Data
    public class ReturnResult {
        
        // 状态码
        private int code;
        // 消息
        private String msg;
        // 数据
        private Object data;
    
        private ReturnResult(){
        
    
        }
    
        private static ReturnResult buildResult(int code, String msg, Object data) {
        
            ReturnResult result = new ReturnResult();
            result.code = code;
            result.msg = msg;
            result.data = data;
            return result;
        }
    
        public static ReturnResult buildSuccessResult(String msg, Object data) {
        
            return buildResult(200, msg, data);
        }
    
        public static ReturnResult buildSuccessResult(Object data) {
        
            return buildSuccessResult("success", data);
        }
    
        public static ReturnResult buildFailureResult(int code, String msg, Object data) {
        
            return buildResult(code, msg, data);
        }
    
        public static ReturnResult buildFailureResult(String msg, Object data) {
        
            return buildFailureResult(500, msg, data);
        }
    
        public static ReturnResult buildFailureResult(String msg) {
        
            return buildFailureResult(500, msg, null);
        }
    }

参考：https://windcoder.com/dawenjianfenpianshangchuanjavabanjiandanshixian

## 3. 压缩与解压缩 ##

@PostMapping("/unzip")
        public ReturnResult unzip(String path){
        
            return ReturnResult.buildSuccessResult(ZipUtil.unzip(path, "E:/usr/local/apps/pmxt-download/merge"));
        }

参考：http://hutool.cn/docs/index.html\#/core/%E5%B7%A5%E5%85%B7%E7%B1%BB/%E5%8E%8B%E7%BC%A9%E5%B7%A5%E5%85%B7-ZipUtil

## 4. 图片压缩 ##

这里我的实现主要有两种：Google图片处理工具与hutool工具，我都用了一下，发现前者将3700kb质量比例双压缩后为1295kb，后者仅是比例压缩就将3700kb压缩为了1100kb，但是前者对图片的处理方式更多，所以用那种，根据自身需求选择

文件夹处理工具类：

package com.example.springboot.common;
    
    import java.io.File;
    import java.text.DecimalFormat;
    import java.util.ArrayList;
    import java.util.List;
    
    public class FileViewer {
        
    
        public static List<String> getListFiles(String path, boolean isdepth) {
        
            List<String> lstFileNames = new ArrayList<String>();
            File file = new File(path);
            return FileViewer.listFile(lstFileNames, file, "jpg", isdepth);
        }
    
        private static List<String> listFile(List<String> lstFileNames, File f,
                                             String suffix, boolean isdepth) {
        
            // 若是目录, 采用递归的方法遍历子目录
            if (f.isDirectory()) {
        
                File[] t = f.listFiles();
                for (int i = 0; i < t.length; i++) {
        
                    if (isdepth || t[i].isFile()) {
        
                        listFile(lstFileNames, t[i], suffix, isdepth);
                    }
                }
            } else {
        
                String filePath = f.getAbsolutePath();
                    if (!suffix.equals("")) {
        
                        int begIndex = filePath.lastIndexOf("."); // 最后一个.(即后缀名前面的.)的索引
                        String tempsuffix = "";
                        if (begIndex != -1) {
        
                            tempsuffix = filePath.substring(begIndex + 1,
                                    filePath.length());
                            if (tempsuffix.equals(suffix) ||  tempsuffix.equals("bmp") || tempsuffix.equals("jpeg") || tempsuffix.equals("png") || tempsuffix.equals("gif")) {
        
                                lstFileNames.add(filePath);
                            }
                        }
                    } else {
        
                        lstFileNames.add(filePath);
                    }
    
            }
            return lstFileNames;
        }
    
        // 递归取得文件夹（包括子目录）中所有文件的大小
        public static long getFileSize(File f) throws Exception// 取得文件夹大小
        {
        
            long size = 0;
            File flist[] = f.listFiles();
            for (int i = 0; i < flist.length; i++) {
        
                if (flist[i].isDirectory()) {
        
                    size = size + getFileSize(flist[i]);
                } else {
        
                    size = size + flist[i].length();
                }
            }
            return size;
        }
    
        public static String FormetFileSize(long fileS) {
        // 转换文件大小
            DecimalFormat df = new DecimalFormat("#.00");
            String fileSizeString = "";
            if (fileS < 1024) {
        
                fileSizeString = df.format((double) fileS) + "B";
            } else if (fileS < 1048576) {
        
                fileSizeString = df.format((double) fileS / 1024) + "K";
            } else if (fileS < 1073741824) {
        
                fileSizeString = df.format((double) fileS / 1048576) + "M";
            } else {
        
                fileSizeString = df.format((double) fileS / 1073741824) + "G";
            }
            return fileSizeString;
        }
    
    }

遍历文件夹下所有图片，过大则进行压缩：

@PostMapping("/selectBySize")
        public ReturnResult selectBySize(String path) {
        
            List<String> flist = FileViewer.getListFiles(path,true);
            for (String s : flist) {
        
                File file = new File(s);
                if (file.isDirectory()) {
        
                    return ReturnResult.buildFailureResult("文件不存在");
                } else {
        
                    if(file.length()>1048576*3){
        
                        ImgUtil.scale(
                                FileUtil.file(s),
                                FileUtil.file(s),
                                0.5f//缩放比例
                        );
    //                    try {
        
    //                        Thumbnails.of(s)
    //                                .scale(0.5f)
    //                                .outputQuality(0.5f)
    //                                .toFile(s);
    //                    } catch (IOException e) {
        
    //                        throw new RuntimeException(e);
    //                    }
                    }
                }
            }
            return ReturnResult.buildSuccessResult(true);
    
        }

参考：[hutool图片处理工具][hutool]  
[Google图片处理工具][Google]

[hutool]: http://hutool.cn/docs/index.html#/core/%E5%9B%BE%E7%89%87/%E5%9B%BE%E7%89%87%E5%B7%A5%E5%85%B7-ImgUtil
[Google]: https://www.cnblogs.com/strongmore/p/14158639.html#autoid-3-0-0