JGit and finding the Head

Question

I'm trying to get my hands on the HEAD commit with JGit:

val builder = new FileRepositoryBuilder()
val repo = builder.setGitDir(new File("/www/test-repo"))
  .readEnvironment()
  .findGitDir()
  .build()

val walk: RevWalk = new RevWalk(repo, 100)

val head: ObjectId = repo.resolve(Constants.HEAD)
val headCommit: RevCommit = walk.parseCommit(head)

I find that it opens the repo fine, but head value is set to null. I wonder why it can't find HEAD?

I'm reading this documentation: http://wiki.eclipse.org/JGit/User_Guide

The repository is constructed just like the doc says, and the RevWalk as well. I'm using the latest version of JGit which is 2.0.0.201206130900-r from http://download.eclipse.org/jgit/maven.

My question: what do I need to change in my code to get JGit to return actual instances of RevCommit instead of null like it now does?

Update: This code:

val git = new Git(repo)
val logs: Iterable[RevCommit] = git.log().call().asInstanceOf[Iterable[RevCommit]]

Gives me this exception: No HEAD exists and no explicit starting revision was specified

The exception is odd, because a simple git rev-parse HEAD tells me 0b0e8bf2cae9201f30833d93cc248986276a4d75, which means there is a HEAD in the repository. I've tried different repositories, mine and from other people.

I'm sorry that I don't know the answer to this question. I just have a comment that rather than saying "I'm using the latest version of JGit" you should state the exact version number. What if someone with a similar problem reads this question a year from now? How will they know which version was "the latest version" when you originally asked the question? — Code-Apprentice, Sep 09 '12 at 20:59

score 31 · Accepted Answer · answered Sep 09 '12 at 21:57

31

You need to point to the Git metadata directory (probably /www/test-repo/.git) when you call setGitDir, not to the working directory (/www/test-repo).

I have to admit I'm not sure what findGitDir is supposed to do, but I've run into this problem before and specifying the .git directory worked.

answered Sep 09 '12 at 21:57

Travis Brown

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I think (but I'm not sure I never got the mechanics of this) that more specifically, he should use either setGitDir or findGitDir, not both. But yeah I've been through a lot of troubles before finding the right combination. – Vince Sep 09 '12 at 22:24
I've just confirmed that specifying the metadata directory with `setGitDir` works, and it doesn't seem to make any difference whether you add `findGitDir` or not. – Travis Brown Sep 09 '12 at 22:44
And here's an example: https://github.com/centic9/jgit-cookbook/blob/master/src/main/java/org/dstadler/jgit/OpenRepository.java – MewX Apr 09 '18 at 14:12

score 6 · Answer 2 · answered Oct 13 '16 at 13:57

For the completeness sake, here is a fully working example how to get the hash for the HEAD commit:

public String getHeadName(Repository repo) {
  String result = null;
  try {
    ObjectId id = repo.resolve(Constants.HEAD);
    result = id.getName();
  } catch (IOException e) {
    e.printStackTrace();
  }
  return result;
}

score 3 · Answer 3 · edited Oct 02 '16 at 14:07

3

For me (using 4.5.0.201609210915-r) the solution was to use just RepositoryBuilder instead of FileRepositoryBuilder. Until I made this change all methods were returning null.

rb = new org.eclipse.jgit.lib.RepositoryBuilder()
    .readEnvironment()
    .findGitDir()
    .build();

headRef = rb.getRef(rb.getFullBranch());
headHash = headRef.getObjectId().name();

edited Oct 02 '16 at 14:07

Tunaki

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answered Oct 02 '16 at 14:02

Ed Randall

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score 1 · Answer 4 · answered Jul 10 '16 at 21:13

1

You can also use val git: Git = Git.open( new File( "/www/test-repo" ) ). JGit will then scan the given folder for the git meta directory (usually .git). If it fails to find this folder, an IOException will be thrown.

answered Jul 10 '16 at 21:13

Taig

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score 0 · Answer 5 · answered May 27 '22 at 13:17

There is not much info available for the usage of findGitDir(), so I thought I share my findings here. So use this code to setup JGit Repository object from anywhere of its working tree:

RepositoryBuilder repositoryBuilder = new RepositoryBuilder();

Repository repo = repositoryBuilder
  .findGitDir(new File("~/workspace/project1/src/main/java"))
  .setMustExist(true)
  .build();

In my case I was using the repo to check its status:

Git git = Git.wrap(repo);
git.status().call();

The code is based on JGit version 5.10.0.202012080955-r

JGit and finding the Head

5 Answers5

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