Where and how does GAE blobstore stores a file (or blob)?

Question

I am new to Google App Engine. I ran (locally) the sample of GAE bolbstore application given in the below link:

https://developers.google.com/appengine/docs/java/blobstore/

It launched a page to choose and submit a file. When I choose a file clicked the submit button:

i) the browser automatically downloads the same file. Why is it again downloading the same file?

ii) it created two files inside the folder 'appengine-generated'. They are:

• d06-XwWoSZVw9HRcnLjZiA
• local_db.bin

What are these files and where did my file store as blob?

Answer 1

Don't worry too much about what happens locally on the dev server.

i) It's just part of the demo, it serves you back the file you just uploaded because of this line:

res.sendRedirect("/serve?blob-key=" + blobKey.getKeyString());

ii) The first would I guess be the file you've just uploaded, the second would be the local copy of mySQL the dev server is using to emulate the datastore itself. Try comparing sizes to the original file you uploaded?

Once you have stored the file you have to access it via the api's provided, what form and where the file is actually stored no longer matters.