获取文件并下载

方式1： 本地文件

@PostMapping("/importTemplate")
    public ResponseEntity<byte[]> importTemplate() {
        String fileName = "company_template.xlsx";
        String fileUrl = properties.getFile() + fileName;


        try {
            File f = new File(fileUrl);
            InputStream in = Files.newInputStream(f.toPath());

            ByteArrayOutputStream out = new ByteArrayOutputStream();
            byte[] buffer = new byte[1024];
            int bytesRead;

            while ((bytesRead = in.read(buffer)) != -1) {
                out.write(buffer, 0, bytesRead);
            }

            byte[] fileData = out.toByteArray();

            HttpHeaders headers = new HttpHeaders();
            headers.setContentType(MediaType.APPLICATION_OCTET_STREAM);
            headers.setContentDispositionFormData("attachment", fileName);
            headers.setContentLength(fileData.length);

            return new ResponseEntity<>(fileData, headers, HttpStatus.OK);
        } catch (IOException e) {
            e.printStackTrace();
            return new ResponseEntity<>(HttpStatus.INTERNAL_SERVER_ERROR);
        }
    }

方式2：远程文件

 @PostMapping("/importTemplate")
 public ResponseEntity<byte[]> importTemplate() {
     String fileName = "company_template.xlsx";
     String fileUrl = properties.getFile() + fileName;

     try {
         URL url = new URL(fileUrl);
         URLConnection conn = url.openConnection();
         InputStream in = conn.getInputStream();

         ByteArrayOutputStream out = new ByteArrayOutputStream();
         byte[] buffer = new byte[1024];
         int bytesRead;

         while ((bytesRead = in.read(buffer)) != -1) {
             out.write(buffer, 0, bytesRead);
         }

         byte[] fileData = out.toByteArray();

         HttpHeaders headers = new HttpHeaders();
         headers.setContentType(MediaType.APPLICATION_OCTET_STREAM);
         headers.setContentDispositionFormData("attachment", fileName);
         headers.setContentLength(fileData.length);

         return new ResponseEntity<>(fileData, headers, HttpStatus.OK);
     } catch (IOException e) {
         e.printStackTrace();
         return new ResponseEntity<>(HttpStatus.INTERNAL_SERVER_ERROR);
     }
 }