如何使用 Java 从 Google Cloud Storage 下载文件？
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How to download a file from Google Cloud Storage with Java?
提问by Tom Jonckheere
I'm developping an application that provides users with an interface where they can download files from our Google Cloud Storage. I wrote unit tests and I could connect to the storage and a file was downloaded.
我正在开发一个应用程序，为用户提供一个界面，他们可以从我们的 Google Cloud Storage 下载文件。我编写了单元测试，我可以连接到存储并下载了一个文件。
Now that I'm (almost) finished with my interface, I wanted to test the whole application. But now I notice I don't really download the file, I download a file with META data about the file I want to download. Something like:
现在我（几乎）完成了我的界面，我想测试整个应用程序。但是现在我注意到我并没有真正下载文件，而是下载了一个包含有关我要下载的文件的 META 数据的文件。就像是：
{
"kind": "storage#object",
"id": "xxxxxxxxxxx/Homer.png/xxxxxxxxxxxx",
"selfLink": "https://www.googleapis.com/storage/xxxxxxxxxxxxxxxx/Homer.png",
"name": "Homer.png",
"bucket": "xxxxxxxxxxxxxxx",
"generation": "xxxxxxxxxxxxxxx",
"metageneration": "1",
"contentType": "image/png",
"updated": "2014-07-17T08:37:28.026Z",
"storageClass": "STANDARD",
"size": "xxxxx",
"md5Hash": "xxxxxxxxxxxxxxxxxxxxx",
"mediaLink": "https://www.googleapis.com/download/storage/xxxxxxxxxxxxxxx/o/Homer.png?generation=xxxxxxxxxxxxxxxxx&alt=media",
"owner": {
"entity": "user-xxxxxxxxxxxxxxxxxxxxxxxxxxxx",
"entityId": "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
},
"crc32c": "xxxxxxxxxx",
"etag": "xxxxxxxxxxxxx"
}
I'm wondering what I'm doing wrong, this is the code I'm using to download the file:
我想知道我做错了什么，这是我用来下载文件的代码：
public byte[] getFileAsByteArray(String bucketName, String fileName)
throws GoogleAppManagerException {
Storage storage = null;
try {
storage = getStorage();
} catch (GeneralSecurityException e) {
throw new GoogleAppManagerException(SECURITY_EXCEPTION + e.getStackTrace(), e);
} catch (IOException e) {
throw new GoogleAppManagerException(IO_EXCEPTION + e.getStackTrace(), e);
}
Get get = null;
ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
try {
get = storage.objects().get(bucketName, fileName);
get.executeAndDownloadTo(outputStream);
} catch (IOException e1) {
throw new GoogleAppManagerException(IO_EXCEPTION + e1.getStackTrace(), e1);
}
return outputStream.toByteArray();
}
采纳答案by jterrace
As you say, currently you're downloading the metadata. You need to use media download to download the object's data.
正如您所说，目前您正在下载元数据。您需要使用媒体下载来下载对象的数据。
Take a look at the sample Java code here: https://developers.google.com/storage/docs/json_api/v1/objects/get
在此处查看示例 Java 代码：https: //developers.google.com/storage/docs/json_api/v1/objects/get
That is the simplest method, using getMediaHttpDownloader().
这是最简单的方法，使用getMediaHttpDownloader().
There is more info on media and the other method, resumable download, here: https://code.google.com/p/google-api-java-client/wiki/MediaDownload
关于媒体和另一种方法的更多信息，可恢复下载，在这里：https: //code.google.com/p/google-api-java-client/wiki/MediaDownload
回答by Anand Mohan
With the latest libraries:
使用最新的库：
Storage storage = StorageOptions.newBuilder()
.setProjectId(projectId)
.setCredentials(GoogleCredentials.fromStream(new FileInputStream(serviceAccountJSON)))
.build()
.getService();
Blob blob = storage.get(BUCKET_URL, RELATIVE_OBJECT_LOCATION);
ReadChannel readChannel = blob.reader();
FileOutputStream fileOuputStream = new FileOutputStream(outputFileName);
fileOuputStream.getChannel().transferFrom(readChannel, 0, Long.MAX_VALUE);
fileOuputStream.close();
