How to fetch a specific commit with JGit

Question

I know from Retrieve specific commit from a remote Git repository that it's possible to fetch a specific commit from a remote git repository.

However, trying to do so from JGit, it's failing. For the same repository, when I run git fetch origin 57eab609d9efda3b8ee370582c3762c0e721033d:HEAD from terminal, the commit I want (with all its ancestors) is fetched from the remote repository. However, when I run the following using JGit, I get an exception:

RefSpec refSpec = new RefSpec()
    .setSourceDestination(commitId, HEAD)
    .setForceUpdate(true);
refs = Lists.newArrayList(refSpec);
git.fetch().setRemote(GIT_REMOTE_NAME)
    .setTimeout(REMOTE_FETCH_TIMEOUT)
    .setTransportConfigCallback(transportConfigurer)
    .setCredentialsProvider(gitCredentials)
    .setTagOpt(TagOpt.FETCH_TAGS)
    .setRefSpecs(refs)
    .call();

The exception is org.eclipse.jgit.errors.TransportException: Remote does not have 57eab609d9efda3b8ee370582c3762c0e721033d available for fetch.

score 3 · Accepted Answer · edited May 23 '17 at 11:53

3

With Git porcelain commands, you can only fetch refs, not specific commits. See also here: Fetch specific commit from remote git repo

The post you refer to only explains how to fetch a specific ref (refs/remotes/origin/branch in the given example) from a remote. I can't see where a specific commit (that is not referred to by a ref) is fetched.

The same applies to JGit: the FetchCommand need to be given a refspec (hence the name setRefSpecs()) to fetch from. With that information, JGit will fetch the commit to which the refspec points to and all its ancestors.

edited May 23 '17 at 11:53

Community

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answered Feb 12 '17 at 19:31

Rüdiger Herrmann

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Well, I'm trying to set the `RefSpec`, but JGit can't find it, since it's the SHA of the `RevCommit`, not the `RefSpec` of a branch or a tag. However, with normal git command, I can fetch with specific commit SHA as per the original question. I looked at the code of `FetchProcess`, and it does call `conn.getRef(spec.getSource())`, which looks only at the `advertisedRefs`, so it seems that it's not implemented in JGit after all – Alaa Nassef Feb 12 '17 at 19:39
One more thing, the accepted answer from the question you referenced is from 2014. As per http://stackoverflow.com/a/30701724/552396, it seems that the functionality I described in my question was implemented in 2015, and it's described well in the Question referred to at the beginning of my question. I really wished it was implemented in JGit. Will try to send to Dev mailing list to see if there are plans for it. – Alaa Nassef Feb 12 '17 at 20:15
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Thanks for pointing this out. I assume the low level APIs of JGit can be used to fetch certain commits, however the FetchCommand does not support this yet. – Rüdiger Herrmann Feb 13 '17 at 04:34
Just for completeness, I asked about that on the developers' mailing list, http://dev.eclipse.org/mhonarc/lists/jgit-dev/msg03273.html, and it seems that it's not yet supported in JGit – Alaa Nassef Feb 15 '17 at 20:21

How to fetch a specific commit with JGit

1 Answers1