如何使用Java从Google云端存储下载文件？

问题描述

我正在开发一个应用程序，为用户提供一个界面，可以从我们的Google云端存储中下载文件。我编写了单元测试，我可以连接到存储并下载文件。

现在我（几乎）完成了我的界面，我想测试整个应用程序。但现在我注意到我并没有真正下载该文件，我下载了一个文件，其中包含有关我要下载的文件的META数据。类似于：

  {
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 ，
更新：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，
所有者：{
entity：user-xxxxxxxxxxxxxxxxxxxxxxxxxxxx，
entityId：xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
}，
crc32c：xxxxxxxxxx ，
etag：xxxxxxxxxxxxx
} 
  

我想知道我做错了，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）{
抛出新的GoogleAppManagerException（SECURITY_EXCEPTION + e.getStackTrace（），e）; 
} catch（IOException e）{
抛出新的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）{
抛出新的GoogleAppManagerException（IO_EXCEPTION + e1.getStackTrace（），e1）; 
} 
返回outputStream.toByteArray（）; 
} 
  

解决方案

如你所说，目前你'下载元数据。您需要使用媒体下载来下载对象的数据。

在这里查看示例Java代码：
getMediaHttpDownloader（）。

有关媒体和其他方法的更多信息，可恢复下载，此处：

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.

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:

{
 "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:

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();
    }

解决方案

As you say, currently you're downloading the metadata. You need to use media download to download the object's data.

Take a look at the sample Java code here:https://developers.google.com/storage/docs/json_api/v1/objects/get

That is the simplest method, using 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

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