REST服务创建空的zip文件

Question

我已经编写了一个休息服务来下载zip文件，但是问题是当没有文件存在时，该服务会下载一个空的zip文件。由于客户要求，我们无法禁用下载zip按钮表单UI。请帮我解决这个问题。 以下是我用于服务和控制器的代码

 public Optional<ZipOutputStream> zippedOutFiles(DownloadZipDTO downloadZipDTO, ServletOutputStream outputStream)
            throws IOException {

        StringBuilder fileLocationBuilder = new StringBuilder();
        int fileSize = 0;
        ZipOutputStream zippedOut = new ZipOutputStream(outputStream);
        Map<String, Integer> fileMap = new HashMap<>();
        LOGGER.info(" Inside download zip service zippedOutFiles ");

        for (DownloadZipEntityDTO files : downloadZipDTO.getDownloadZipEntityList()) {
            fileSize = fileSize + files.getFileSize();
            fileLocationBuilder.setLength(0);
            fileLocationBuilder.append(files.getFileLocation());
            Resource resource = new FileSystemResource(new File(fileLocationBuilder.toString()));
            if (resource.exists()) {
                checkDuplicateFiles(resource, fileMap);

                ZipEntry entry = fileMap.get(resource.getFilename()) > 0
                        ? new ZipEntry(resource.getFilename().substring(0, resource.getFilename().lastIndexOf('.'))
                                + "_" + fileMap.get(resource.getFilename()).toString()
                                + resource.getFilename().substring(resource.getFilename().lastIndexOf('.')))
                        : new ZipEntry(resource.getFilename());

                entry.setSize(resource.contentLength());
                entry.setTime(System.currentTimeMillis());
                zippedOut.putNextEntry(entry);
                StreamUtils.copy(resource.getInputStream(), zippedOut);
                zippedOut.closeEntry();
            } else {
                zippedOut.finish();
                zippedOut.close();
                throw new Exception(" No file to zip");
            }
        }
        zippedOut.finish();
        zippedOut.close();

        if ((fileSize) / 1024 > CasperProperties.getMaxFileUploadSize()) {
            LOGGER.warn("Total file size is exceeded ", fileSize);
        }

        return Optional.of(zippedOut);
    }


Controller:
Optional<ZipOutputStream> zippedOut = downloadZipService.zippedOutFiles(downloadZipDTO,
                        httpResponse.getOutputStream());
                if (zippedOut.isPresent()) {
                    LOGGER.info("Inside submission Download zip controller setting response data");
                    serviceResponse.setResponseData(zippedOut);

                    String zippedOutName = (dcCodeID).toString().concat("_").concat("Submission")
                            .concat(CasperUtils.getDateFormatInString(new Date()));
                    return ResponseEntity.ok()
                            .header(HttpHeaders.CONTENT_DISPOSITION, "attachment;filename=\"" + zippedOutName + "\"")
                            .body(serviceResponse);
                } else {
                    return ResponseEntity.noContent().build();
}
            }