How to “cat” a file in JGit?

Question

A while back I was looking for an embeddable distributed version control system in Java, and I think I have found it in JGit, which is a pure Java implementation of git. How

Answer 1

You can read the content of a given filepath as follows. Please be aware that the TreeWalk can be null if no path was found in the given tree. So it requires some specific handling.

public String readFile(RevCommit commit, String filepath) throws IOException {
    try (TreeWalk walk = TreeWalk.forPath(repo, filepath, commit.getTree())) {
        if (walk != null) {
            byte[] bytes = repo.open(walk.getObjectId(0)).getBytes();
            return new String(bytes, StandardCharsets.UTF_8);
        } else {
            throw new IllegalArgumentException("No path found.");
        }
    }
}

For example:

ObjectId head = repo.resolve(Constants.HEAD);
RevCommit last = repo.parseCommit(head);
readFile(last, "docs/README.md")

This answer is written with JGit 4.8.0.