GWT GAE Upload through Blob

Question

If I'm using GWT File widget and form panel, can someone explain how to handle upload on blobstore on google application engine??

Answer 1

Google blobstore is specifically designed to upload and serve blobs via http. Blobstore service (obtained using BlobstoreServiceFactory.getBlobstoreService()) generates http post action for you to use in the html form. By posting file to it you upload your blob to the blobstore. When you generate this action you provide a path to the handler (servlet) where you have access to uploaded blob key:

Map<String, BlobKey> blobs = blobstoreService.getUploadedBlobs(req);
BlobKey blobKey = blobs.get("data");

Note, that "data" is the file field in your form. All you have is a key to the blob (your file). From here you take control - you can save this key for later and/or immediately serve the blob on a page (using key):

BlobKey blobKey = new BlobKey(req.getParameter("blob-key"));
blobstoreService.serve(blobKey, res);

Of course, for details see Google documentation.

One nice feature of the blobstore that it's integrated with Google Mapper (rudimentary map-reduce) service (work in progress) which lets you process files uploaded as blobs line by line: http://ikaisays.com/2010/08/

Answer 2

Take a look at gwtupload. There are examples on how to use it with GAE Blobstore.