1）安装js-file-download

npm i -S js-file-download

2）编写下载的页面

<template>
    <div>
        <el-button @click="download">下载</el-button>
    </div>
</template>

<script>
    import fileDownload from 'js-file-download'
    import request from '@/request'
    export default {
        methods: {
            download() {
                request.postDownload('file/download').then(res => {
                    const disposition = res.headers["content-disposition"]
                    //获取文件名
                    let fileName = disposition.substring(disposition.indexOf("filename=") + 9);
                    if (window.navigator.userAgent.indexOf("Firefox") > -1) {
                        fileName = fileName.substring(fileName.indexOf("-8?B?") + 5, fileName.indexOf("?="))
                        fileName = base64Util.decode(fileName);
                    } else {
                        fileName = decodeURIComponent(fileName);
                    }
                    fileDownload(res.data, fileName)
                }).catch(err => {
                    console.log(err)
                })
            }
        },

    }

</script>

<style scoped>

</style>

这里网络请求使用的axios，对其进行了封装。下载的方法很简单，主要是获取响应头中的文件名

3）编写下载的工具类

package com.zys.demo.util;

import lombok.extern.slf4j.Slf4j;

import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.net.URLEncoder;

@Slf4j
public class FileUtil {

    /**
     * 通过流下载文件
     *
     * @param fileName 文件名
     * @param response
     * @throws IOException
     */
    public static void downloadFile(String filePath, String fileName, HttpServletResponse response) throws IOException {
        File file = new File(filePath + File.separator + fileName);
        InputStream in = new FileInputStream(file);
        //允许暴露content-disposition，默认不暴露
        response.setHeader("Access-Control-Expose-Headers", "content-disposition");
        response.setCharacterEncoding("UTF-8");
        response.setContentType("application/octet-stream");
        response.setHeader("content-disposition", "attachment;filename=" + URLEncoder.encode(fileName, "UTF-8"));
        int len = 0;
        byte bytes[] = new byte[1024];
        OutputStream out = response.getOutputStream();
        while ((len = in.read(bytes)) > 0) {
            out.write(bytes, 0, len);
        }
        in.close();
        out.close();
    }

}

需要注意的是必须设置响应头的Access-Control-Expose-Headers，也就是要暴露的信息，否则在前端无法获取到文件名。

4）编写下载的接口

package com.zys.demo.controller;

import com.zys.demo.util.FileUtil;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@RestController
@RequestMapping("/api/file")
public class FileController {

    @PostMapping("/download")
    public void downloadFile(HttpServletResponse response) throws IOException {
        FileUtil.downloadFile("D://temp",  "test.txt", response);
    }
}

启动后，点击下载按钮即可下载。文件需事先存在于对应位置。