Mercurial API for Java?

Question

Is there a plain API to access Mercurial repositories from Java?

There are plugins for Netbeans and Eclipse, but unlike their Subversion counterparts, they do not use a common lower-level library but bring their own wrappers to call out to the Mercurial binary. Calling the binary would be okay (for now), but it seems very difficult to use those plugins in standalone applications (outside of the IDE they were built for).

There is also HgKit, but that is very pre-alpha.

Answer 1

A new option is JavaHg, which gives you a high-level Java API. The unit tests give a good example of how it is to program with it (as of JavaHg 0.1):

public void commitTest() throws IOException {
    Repository repo = getTestRepository();
    writeFile("x", "abc");

    CommitCommand commit = CommitCommand.on(repo);
    StatusCommand status = StatusCommand.on(repo);

    List<StatusLine> statusLines = status.lines();
    Assert.assertEquals(1, statusLines.size());
    Assert.assertEquals(StatusLine.Type.UNKNOWN, statusLines.get(0).getType());

    AddCommand.on(repo).execute();
    statusLines = status.lines();
    Assert.assertEquals(1, statusLines.size());
    Assert.assertEquals(StatusLine.Type.ADDED, statusLines.get(0).getType());

    commit.message("Add a file").user("Martin Geisler");
    Changeset cset = commit.execute();
    Assert.assertEquals("Martin Geisler", cset.getUser());
    statusLines = status.lines();
    Assert.assertEquals(0, statusLines.size());
}

It interacts with the Mercurial command server present in version 1.9 and later. This means that there will be a persistent Mercurial process around that accepts multiple commands and so you avoid the startup overhead normally associated with launching Mercurial. We expect that it will be used in a coming version of MercurialEclipse. (I'm one of the authors of JavaHg.)

Answer 2

hg4j has more (i.e. clone) functionality now and appears to be under actual development

Answer 3

Have you looked at Jython? As far as I can see here, it should help using the python mercurial modules from within a Java environment, just like JRuby does for Ruby.

Answer 4

The Maven SCM plugin seems to have a Mercurial provider available. However, I don't know how applicable that provider is in your case (ie how deeply it is tied to Maven architecture and/or how it interfaces with hg).

Answer 5

There is also a hg4j but for now it only allows reading the repository.