从服务器上下载文件（app远程升级）

/**
     * 最新apk
     */
    @ApiOperation("最新apk")
    @GetMapping("/getApk")
    public R getApk(HttpServletResponse response) {
          
   
        try {
          
   
            // 下载的文件的路径
            File file = new File(downloadPath);   // downloadPath为文件所在文件夹路径,如 D:destopapk
            // 获取该路径下所有文件
            File[] files = file.listFiles();
            long createTime = 0;
            // 获取最新的文件
            for (File file1 : Arrays.asList(files)) {
          
   
                if (file1.lastModified() > createTime) {
          
   
                    file = file1;
                    createTime = file1.lastModified();
                }
            }

            if(file.exists()){
          
   
                // 以流的形式下载文件。
                InputStream fis = new BufferedInputStream(new FileInputStream(file.getPath()));
                byte[] buffer = new byte[fis.available()];
                fis.read(buffer);
                fis.close();
                // 清空response
                response.reset();
                // 设置response的Header
                response.addHeader("Content-Disposition", "attachment;filename=" + file.getName());
                response.addHeader("Content-Length", "" + file.length());
                response.addHeader("Content-Type", "application/vnd.android.package-archive apk");
                OutputStream toClient = new BufferedOutputStream(response.getOutputStream());
                response.setContentType("application/octet-stream");
                toClient.write(buffer);
                toClient.flush();
                toClient.close();
            }

            log.info("/getApk 获取最新apk成功！");
            return R.ok();
        } catch (Exception e) {
          
   
            log.error("/getApk 获取最新apk失败：", e);
            return R.error(e.toString());
        }
    }