trying to retrieve file from blobstore and send it as mail attachment using google app engine

Question

I am trying to design an application that would require me to retrieve data stored in blobstore and send it as attachment. Does google app engine allow this? From the documentation, i could not find a way to retrieve data from blobstore for processing within the app.. can someone please tell me how to accomplish this? Code examples and/or pointers to related online resources would be really helpful.

Answer 1

As of now, it seems this isn't possible. You can only cause the the file to be sent to the client .

It's possible you could do what you need using a Datastore Blob ?

It's worth also noting that the Blobstore is "experimental" and may change. It's possible additional functionality may be added that would allow what you'r trying to do.

Answer 2

您现在可以使用BlobReader从blobstore读取数据， BlobReader提供了一个简单的，类似文件的界面。

Answer 3

You can use BlobstoreInputStream to do almost the same thing as BlobReader do.

https://developers.google.com/appengine/docs/java/javadoc/com/google/appengine/api/blobstore/BlobstoreInputStream

BlobstoreInputStream provides an InputStream view of a blob in Blobstore. It is thread compatible but not thread safe: there is no static state, but any multithreaded use must be externally synchronized.

Answer 4

This can be accomplished in two steps using the code from the Complete Sample App. http://code.google.com/appengine/docs/java/blobstore/overview.html#Complete_Sample_App

1) Write a servlet that takes a blobkey and returns the contents of the blob.

public void doGet(HttpServletRequest req, HttpServletResponse res)
    throws IOException {
        BlobKey blobKey = new BlobKey(req.getParameter("blob-key"));
        blobstoreService.serve(blobKey, res);
    }

2) Within your application, use the URLFetchService.fetch(java.net.URL url) with the proper blobkey to retrieve the blob (as a stream) and attach it to the email.