How to call git show --first-parent in jgit?

Question

I need to get the commits from master that are not of type merge and do not come from other branches (they were directly put on master). The git command is

git log --no-merges --first-parent

How can I do this using JGit? I managed to get the commits that are not of type merge using

RevFilter.NO_MERGES

But how can I get the commits that were commited direct into master branch?

Answer 1

For getting the first parent, you could just call the RevCommit.getParent() and work your way from there.

The rationale behind not using a RevWalk for visiting the tree is that RevWalk walks through revs without following the hierarchy -- i.e., if you didn't read the commit, it's parent will be read --, which is not what --first-parent does, and what we want here.

So Rüdiger Herrmann's answer will fail to remove the commits made on (n+1,...)^th branches. It would only remove the first commit made on those branches.

Code

Repository repo = git.getRepository();
try (RevWalk walk = new RevWalk(repo)) {
    RevCommit head = walk.parseCommit(repo.getRef(MASTER).getObjectId());
    int count = 0;
    while (head != null) {
        count++;
        RevCommit[] parents = head.getParents();
        if (parents != null && parents.length > 0) {
            head = walk.parseCommit(parents[0]);
        } else {
            head = null;
        }
    }
    return count;
}

This is converted from groovy source

Notes

1. The call to walk.parseCommit(parents[0]) is required as the commits returned by .getParents() will not be parsed completely, and will give null on calling .getParents() on themselves.
2. This was written for finding version code from git repo for Android build script (gradle) based on my another answer. (see source)