"I don't have any direct experience writing anything like this from scratch with Vim, but here's what you'll want to look for examples to follow.
You probably want a filetype plugin (ftplugin) for .java files:
A filetype plugin is like a global plugin, except that it sets options and defines mappings for the current buffer only. See |add-filetype-plugin| for how this type of plugin is used.
And use it with a mapleader+hotkey:
To define a mapping which uses the ""mapleader"" variable, the special string """" can be used. It is replaced with the string value of ""mapleader"". If ""mapleader"" is not set or empty, a backslash is used instead. ... To define a mapping which uses the ""mapleader"" variable, the special string """" can be used. It is replaced with the string value of ""mapleader"". If ""mapleader"" is not set or empty, a backslash is used instead.
You might have a look at the Vim JDE scripts, or this guide on configuring Vi(m) for Java development. This page has some information on using javac in Vim."
