dein.vimのアレ

config.vim

function! s:get_sid_prefix() abort
  return matchstr(expand('<sfile>'), '^function \zs<SNR>\d\+_\zeget_sid_prefix$')
endfunction
let s:sid_prefix = s:get_sid_prefix()
delfunction s:get_sid_prefix

function! s:tes() abort
  setlocal omnifunc=javacomplete#Complete
endfunction

call dein#add('artur-shaik/vim-javacomplete2')
call dein#config('artur-shaik/vim-javacomplete2', {
      \ 'hook_source': 'autocmd FileType java call ' . s:sid_prefix . 'tes()'
      \ })