使用 JGit 从 Git 检索提交消息日志

我只想从 Git 存储库检索提交日志，其中包含您在特定存储库上完成的所有提交的消息。我找到了一些实现此目的的代码片段，并以异常结束。

try {
    FileRepositoryBuilder builder = new FileRepositoryBuilder();
    Repository repo = builder.setGitDir(new File("https://github.com/name/repository.git")).readEnvironment().findGitDir().build();
    RevWalk walk =new RevWalk(repo);
    ObjectId head = repo.resolve(Constants.HEAD);
    RevCommit commit =walk.parseCommit(head);
    Git git =new Git(repo);
    Iterable<RevCommit> gitLog = git.log().call();
    Iterator<RevCommit> it = gitLog.iterator();
    while(it.hasNext())
    {
        RevCommit logMessage = it.next(); 
        System.out.println(logMessage.getFullMessage());
    }
}
catch(Exception e) {
    e.printStackTrace();
}

然而它给了我：

org.eclipse.jgit.api.errors.NoHeadException: No HEAD exists and no explicit starting revision was specified exception.

我该如何摆脱这个？我正在使用 org.eclipse.jgit JAR 版本 2.0.0.201206130900-r

这是执行上述操作的正确代码。

FileRepositoryBuilder builder = new FileRepositoryBuilder();
Repository repo = builder.setGitDir(new File("localrepositary"+"\\.git")).setMustExist(true).build();
Git git = new Git(repo);
Iterable<RevCommit> log = git.log().call();
for (Iterator<RevCommit> iterator = log.iterator(); iterator.hasNext();) {
  RevCommit rev = iterator.next();
  logMessages.add(rev.getFullMessage());
}