Google app engine 谷歌应用引擎和云存储API

我正在尝试通过一个GAE应用程序从谷歌云存储获取文件

我通过params（一个简单的

HTML

表单）获取bucket和filename，并调用Servlet：

String bucket = req.getParameter("bucket");
String filename = req.getParameter("filename");

BlobstoreService blobstoreService = BlobstoreServiceFactory
        .getBlobstoreService();
BlobKey blobKey = blobstoreService.createGsBlobKey("/gs/" + bucket
        + "/" + filename);
blobstoreService.serve(blobKey, resp);

我在localhost和GAE上收到此错误：

The API package 'blobstore' or call 'CreateEncodedGoogleStorageKey()' was not found.

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有解决办法吗？如果是，请分享。甚至我也面临同样的问题。