SpringBoot+MybatisPlus--文件上传和下载实例

文件上传时，file是一个临时文件，需要转存到指定位置，否则本次请求完成后临时文件就被删除

Controller后台代码：

package com.itheima.reggie.controller;

import com.itheima.reggie.common.R;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.multipart.MultipartFile;

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

/**
 * 文件上传和下载
 */
@RestController
@RequestMapping("/common")
public class CommonController {

    @Value("${reggie.path}")
    private String basePath;

    @PostMapping("/upload")
    public R<String> upload(MultipartFile file) {
        // 获取原始的文件名
        String filename = file.getOriginalFilename();
        // 获取的后缀
        String suffix = filename.substring(filename.lastIndexOf("."));
        // 通过UUID生成一个文件名防止文件重复后覆盖原文件
        filename = UUID.randomUUID().toString() + suffix;
        // 创建一个目录对象
        File dir = new File(basePath);

        // 目录不存在时创建
        if (dir.exists()) {
            dir.mkdirs();
        }
        try {
            // 将临时文件储存到指定位置
            file.transferTo(new File(basePath + filename));
        } catch (IOException e) {
            e.printStackTrace();
        }
        // 返回文件名称
        return R.success(filename);
    }

    @GetMapping("/download")
    public void download(String name, HttpServletResponse response) {
        try {
            // 从本地磁盘进行读取
            FileInputStream fileInputStream = new FileInputStream(new File(basePath + name));
            // 从response中获取输出流对象写回游览器，在游览器展示图片
            ServletOutputStream outputStream = response.getOutputStream();
            response.setContentType("image/jpeg"); //设置响应回去的是图片文件
            // 进行读取
            int len = 0;
            byte[] bytes = new byte[1024];
            // 当bytes没有数据的时候 返回-1
            while((len = fileInputStream.read(bytes)) != -1) {
                outputStream.write(bytes, 0, len);
                outputStream.flush();
            }
            outputStream.close();
            fileInputStream.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

前端：（来自黑马）

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>文件上传</title>
  <!-- 引入样式 -->
  <link rel="stylesheet" href="../../plugins/element-ui/index.css" />
  <link rel="stylesheet" href="../../styles/common.css" />
  <link rel="stylesheet" href="../../styles/page.css" />
</head>
<body>
   <div class="addBrand-container" id="food-add-app">
    <div class="container">
        <el-upload class="avatar-uploader"
                action="/common/upload"
                :show-file-list="false"
                :on-success="handleAvatarSuccess"
                :before-upload="beforeUpload"
                ref="upload">
            <img v-if="imageUrl" :src="imageUrl" class="avatar"></img>
            <i v-else class="el-icon-plus avatar-uploader-icon"></i>
        </el-upload>
    </div>
  </div>
    <!-- 开发环境版本，包含了有帮助的命令行警告 -->
    <script src="../../plugins/vue/vue.js"></script>
    <!-- 引入组件库 -->
    <script src="../../plugins/element-ui/index.js"></script>
    <!-- 引入axios -->
    <script src="../../plugins/axios/axios.min.js"></script>
    <script src="../../js/index.js"></script>
    <script>
      new Vue({
        el: '#food-add-app',
        data() {
          return {
            imageUrl: ''
          }
        },
        methods: {
          handleAvatarSuccess (response, file, fileList) {
              this.imageUrl = `/common/download?name=${response.data}`
          },
          beforeUpload (file) {
            if(file){
              const suffix = file.name.split('.')[1]
              const size = file.size / 1024 / 1024 < 2
              if(['png','jpeg','jpg'].indexOf(suffix) < 0){
                this.$message.error('上传图片只支持 png、jpeg、jpg 格式！')
                this.$refs.upload.clearFiles()
                return false
              }
              if(!size){
                this.$message.error('上传文件大小不能超过 2MB!')
                return false
              }
              return file
            }
          }
        }
      })
    </script>
</body>
</html>