如果文件不存在，java将返回空响应

Question

我用这段代码从angular应用程序下载了一张图片

    @RequestMapping("/files/{merchant_id}")
    public ResponseEntity<byte[]> downloadLogo(@PathVariable("merchant_id") Integer merchant_id) throws IOException {
        File file = new File(UPLOADED_FOLDER, merchant_id.toString() + "/merchant_logo.png");
        InputStream in = FileUtils.openInputStream(file);

        final HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.IMAGE_PNG);

        return new ResponseEntity<byte[]>(IOUtils.toByteArray(in), headers, HttpStatus.CREATED);
    }

但当我试图下载一张没有找到的图片时，我得到了NPE，这是正常的。当找不到图像文件时，如何返回空响应？比如：

return ResponseEntity.ok(...).orElse(file.builder().build()));

你能给我一些建议如何解决这个问题吗

Answer 1

只需选择一个不带body参数的ResponseEntity构造函数来创建ResponseEntity

    File file = new File(UPLOADED_FOLDER, merchant_id.toString() + "/merchant_logo.png");
    final HttpHeaders headers = new HttpHeaders();
    headers.setContentType(MediaType.IMAGE_PNG);

    if (!file.exists()) {
        return new ResponseEntity<byte[]>(headers,HttpStatus.NOT_FOUND);
    }else{
        InputStream in = FileUtils.openInputStream(file);
        return new ResponseEntity<byte[]>(IOUtils.toByteArray(in), headers, HttpStatus.OK);
    }

我将其更改为当图像不存在时返回404状态码，当图像存在时返回200状态码，这更符合HTTP状态码的语义