File myFile = new File(repository.getDirectory().getParent(), "testfile");
                if(!myFile.createNewFile()) {
                    throw new IOException("Could not create file " + myFile);
                }
//... then write bytes to the file

 add

commit

Array[byte] content = ???
String filePath = ???

Git git = Git.open(repoPath);
Repository repo = git.getRepository;
repo.addOrUpdateFileContent(filePath, content);
git.commit().call();