Eclipse provides a feature called local history, which is basically a simplistic version control system that is updated every time you save a file. Using this local history, you can view diffs against previously saved versions of your file or revert to one of those revisions.
Eclim supports updating eclipse's local history when writing files from vim, but by default this feature is disabled unless gvim was started from the eclipse gui, in which case eclim will honor the default eclipse editor behavior and update the local history. You can turn this feature on in all cases by adding the following to your vimrc:
let g:EclimKeepLocalHistory = 1
:History - Opens a temporary buffer showing the local history for the current file. In this buffer you can perform the following actions using the specified key bindings:
:HistoryClear[!] - Clears the local history for the current file. When the bang (!) is supplied, you are not prompted before clearing the history.
:HistoryDiffNext - While the history buffer is open, this command allows you to diff the current file against the next entry in the history stack.
:HistoryDiffPrev - Just like :HistoryDiffNext but diffs against the previous entry in the stack.
When writing to the local history, eclim simply proxies the request to eclipse, so all eclipse settings are honored. To modify these settings you currently have to do so inside of the eclipse gui. First shut down eclimd if you are running a headless version, then open the eclipse gui and navigate to:
And there you can edit your settings as necessary.