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.

Answer 1

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.

Answer 2

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; }