如何从 Google Cloud Storage 下载文件并将其返回到 Spring 控制器中

Question

我有一个 Spring Boot 应用程序。用户可以登录我的应用程序并上传文件。用户的所有文件都存储在Google Cloud Storage中。现在，我希望用户能够下载他们的文件。所以，我必须从云存储下载文件。我不知道我的控制器应该是什么样子。使用我当前的代码，我得到一个空文件。上传已经完成，连接也正常。

public static Blob downloadFile(Storage storage, String fileName){

        Blob blob = storage.get(BUCKET_NAME, fileName);

        return blob;

    }

@RequestMapping(value = "/downloadFileTest")

    @ResponseBody

    public void downloadFile(HttpSession session,

            HttpServletResponse response) {

        Storage storage = de.msm.msmcenter.service.cloudstorage.Authentication.getStorage();

        Blob blob = de.msm.msmcenter.service.cloudstorage.Authentication.downloadFile(storage,"test.txt");

        ReadChannel readChannel = blob.reader();

        InputStream inputStream = Channels.newInputStream(readChannel);

        try {

            response.setContentType("application/force-download");

            response.setHeader("Content-Disposition", "attachment; filename=test.txt");

            IOUtils.copy(inputStream, response.getOutputStream());

            response.flushBuffer();

            inputStream.close();

        } catch (Exception e){

            e.printStackTrace();

        }

    }

我实际上希望能够下载任何文件，而不仅仅是txt。当用户打开链接时，会下载名为 test.txt 的文件，但它是空的。

Answer 1

看起来您只想授予用户下载文件的权限。解决方案是使用Signed URL，它可以让您向用户提供一个 URL 以在有限的时间内访问/下载对象。如果您将用户直接重定向到该 URL，下载将立即开始。

Answer 2

我将代码更改为：public static String downloadFile(Storage storage, String fileName){        Blob blob = storage.get(BUCKET_NAME, fileName);        String PATH_TO_JSON_KEY = "/your/path";        URL signedUrl = null;        try {            signedUrl = storage.signUrl(BlobInfo.newBuilder(BUCKET_NAME, fileName).build(),                    1, TimeUnit.DAYS, SignUrlOption.signWith(ServiceAccountCredentials.fromStream(                            new FileInputStream(PATH_TO_JSON_KEY))));        } catch (IOException e) {            e.printStackTrace();        }        return signedUrl.toString();    }

Answer 3

#将此行添加到 spring-boot application.properties 文件 spring.cloud.gcp.credentials.location=classpath:key.json&nbsp; &nbsp; // read/download objectspublic static ResponseEntity<byte[]> getObjectFromGCP(String yourfileName) throws IOException {&nbsp; &nbsp; String objectNameWithLocation ="your file location with file name in GCP bucket";&nbsp; &nbsp; &nbsp;//create your storage object with your credentials&nbsp; &nbsp;&nbsp;&nbsp; &nbsp; Credentials credentials = GoogleCredentials.fromStream(new&nbsp;&nbsp; &nbsp; &nbsp; &nbsp;ClassPathResource("key.json").getInputStream());&nbsp; &nbsp; Storage storage = StorageOptions.newBuilder().setCredentials(credentials).build().getService();&nbsp; &nbsp; BlobId blobId = BlobId.of(bucketName, objectNameWithLocation);&nbsp; &nbsp; Blob blob = storage.get(blobId);&nbsp; &nbsp; return ResponseEntity.ok().contentType(MediaType.valueOf(FileTypeMap.getDefaultFileTypeMap().getContentType(yourfileName)))&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; .body(blob.getContent(BlobSourceOption.generationMatch()));}