How to “git log --follow ” in JGit? (To retrieve the full history including renames)

Question

How do I have to extend the following logCommand, to get the --follow option of the git log command working?

Git git = new Git(myRe         


        

Answer 1

I recall trying OneWorld's solution on a previous occasion, and while it worked, it was very slow. I thought I'd google around to see if there were any other possibilities out there.

Yes, in this Eclipse thread, there was a suggestion of using org.eclipse.jgit.revwalk.FollowFilter and to look for a use-example in RevWalkFollowFilterTest.java.

So thought I'd give that a try, resulting in code like that looks like this:

private static class DiffCollector extends RenameCallback {
    List diffs = new ArrayList();

    @Override
    public void renamed(DiffEntry diff) {
        diffs.add(diff);
    }
}

private DiffCollector diffCollector;

private void showFileHistory(String filepath)
{
    try
    {
        Config config = repo.getConfig();
        config.setBoolean("diff", null, "renames", true);

        RevWalk rw = new RevWalk(repo);
        diffCollector = new DiffCollector();

        org.eclipse.jgit.diff.DiffConfig dc = config.get(org.eclipse.jgit.diff.DiffConfig.KEY);
        FollowFilter followFilter =
                 FollowFilter.create(filepath, dc);
        followFilter.setRenameCallback(diffCollector);
        rw.setTreeFilter(followFilter);
        rw.markStart(rw.parseCommit(repo.resolve(Constants.HEAD)));

        for (RevCommit c : rw)
        {
            System.out.println(c.toString());
        }
    }
    catch(...

The results were, erm, ok I guess... The RevWalk did manage to walk through a simple rename of a file in the git-repo's history (performed by a "git mv {filename}" action).

However, it was unable to handle messier situations, such as when a colleague performed this set of actions in the repo's history:

• 1st commit: Renamed a file with "git mv"
• 2nd commit: Added a copy of that file in a new sub-folder location
• 3rd commit: Deleted the old location's copy

In this scenario, JGit's follow capabilities will only get me the from the head to that 2nd commit, and stop there.

The real "git log --follow" command, however, seems to have enough smarts to figure out that:

• The file added in the 2nd commit is the same as that in the 1st commit (even though they are in different locations)
• It will give you the entire history:
  • from HEAD-to-2nd-commit (added copy of newly-named file in new location)
  • skips any mention of the 3rd-commit (delete of old file in old path)
  • followed by the 1st-commit and its history (old location and name of file)

So JGit's follow capabilities seem a little weaker compared to real Git. Ah well.

But anyway, I can confirm that using JGit's FollowFilter technique did work a lot faster than the previously suggested technique.