JGit: Is there a thread safe way to add and update files - multithreading

Question

The easy way to add or update files in JGit is like this:
git.add().addFilepattern(file).call()
But that assumes that the file exists in the Git working directory.
If I have a multi-threaded setup (using Scala and Akka), is there a way to work only on a bare repository, writing the data directly to JGit, avoiding having to first write the file in the working directory?
For getting the file, that seems to work with:
git.getRepository().open(objId).getBytes()
Is there something similar for adding or updating files?

Answer 1

"Add" is a high-level abstraction that places a file in the index. In a bare repository, you lack an index, so this is not a 1:1 correspondence between the functionality. Instead, you can create a file in a new commit. To do this, you would use an ObjectInserter to add objects to the repository (one per thread, please). Then you would:
Add the contents of the file to the repository, as a blob, by inserting its bytes (or providing an InputStream).
Create a tree that includes the new file, by using a TreeFormatter.
Create a commit that points to the tree, by using a CommitBuilder.
For example, to create a new commit (with no parents) that contains only your file:
ObjectInserter repoInserter = repository.newObjectInserter();
ObjectId blobId;
try
{
// Add a blob to the repository
ObjectId blobId = repoInserter.insert(OBJ_BLOB, "Hello World!\n".getBytes());
// Create a tree that contains the blob as file "hello.txt"
TreeFormatter treeFormatter = new TreeFormatter();
treeFormatter.append("hello.txt", FileMode.TYPE_FILE, blobId);
ObjectId treeId = treeFormatter.insertTo(repoInserter);
// Create a commit that contains this tree
CommitBuilder commit = new CommitBuilder();
PersonIdent ident = new PersonIdent("Me", "me#example.com");
commit.setCommitter(ident);
commit.setAuthor(ident);
commit.setMessage("This is a new commit!");
commit.setTreeId(treeId);
ObjectId commitId = repositoryInserter.insert(commit);
repoInserter.flush();
}
finally
{
repoInserter.release();
}
Now you can git checkout the commit id returned as commitId.