ObjectId head = repository.resolve("HEAD^{tree}");
System.out.println("Printing diff between tree: " + oldHead + " and " + head);
// prepare the two iterators to compute the diff between
ObjectReader reader = repository.newObjectReader();
CanonicalTreeParser oldTreeIter = new CanonicalTreeParser();
oldTreeIter.reset(reader, oldHead);
CanonicalTreeParser newTreeIter = new CanonicalTreeParser();
newTreeIter.reset(reader, head);