I'm newbie in GAE and just trying to work out basic principles of my future web app. So I looking to java to design my app. And I want realize which is better way to create admin panel? An admin should be allowed to manage posts and users for example.
I heard that Django has build-in admin panel, but I do not experienced in Python.
The great thing about going the Python/Django route is that there are great tutorials that walk you through the process step-by-step.
Google's own example of how to get Django running.
If you're comfortable with programming, Python is a very easy language to pickup. As you mentioned, Django provides a great admin interface that does a lot of the work for you.
If you do decide to use Java, you'll have to build the admin interface from scratch, which generally takes quite a bit of time (if you want to do it right and do it well). I recommend that you use a framework to help you in the process, and here Google has some documentation on which frameworks work in GAE.