I used to write small Java MIDlets using just GNU Emacs because the laptop I was using at the time was too old and slow to run NetBeans.

I have to say that since the Javadoc format for documentation is the best format ever, I was productive anyway.

Actually, it made me get very very quick at browsing documentation and appreciate it.

Also, by browsing documentation manually, I got to discover many neat stuff within the default-provided Java packages.

... Did you know you can do neat stuff with java.awt.Robot? ;)

Spacemacs is a better Emacs with Vi keybinding and preconfigured programming modes for major languages.

there is: https://github.com/syl20bnr/spacemacs

There is a Django layer in it, you can start runserver witha keystroke, open settings.py with another keystroke, run all tests, etc..

Seriously, people should stop over customizing their .emacs.d . I use mostly default (community) config from Spacemacs and it works just fine. You can use both vi keybinding and emacs keybinding at the sametime in Spacemacs. I reduced 2k+ lines init.el config to about 200 lines in Spacemacs.