在没有使用JGit的父提交（第一次提交）的情况下显示更改/差异

Question

[当我在存储库中进行第一次提交的git show commit时，我会看到所有文件以及文件的差异（即，所有要添加的行）]

$ git show cb5d132
commit cb5d13286cf9d14782f0e10445456dfe41072f55
Author: tw2 tw2LastName <tw2>
Date:   Thu Oct 23 05:15:09 2014 -0400

   Initial Commit

diff --git a/README.txt b/README.txt
new file mode 100644
index 0000000..96d156e
--- /dev/null
+++ b/README.txt
@@ -0,0 +1 @@
+First Line in README file!
\ No newline at end of file

jgit show似乎没有获得相似的信息，如何使用JGit API获得相似的输出？我可以使用DiffFormatter，但似乎需要baseTree和commitTree，想知道如何才能使DiffFormatter在存储库中的第一次提交上工作。

ByteArrayOutputStream os = new ByteArrayOutputStream();
DiffFormatter df = new DiffFormatter( os )
RawTextComparator cmp = RawTextComparator.DEFAULT;

df.setRepository(repository);
df.setDiffComparator(cmp);
df.setDetectRenames(true);

// wondering how to use the API if we do not have baseCommit.
List<DiffEntry> diffEntries = df.scan(??baseCommitTree??, firstCommit.getTree());
for (DiffEntry diffEntry : diffEntries) {                
   df.format(diffEntry);
}
System.out.println(df.toString());

Answer 1

使用o.e.jgit.treewalk.EmptyTreeIterator将第一次提交与以下内容进行比较：

AbstractTreeIterator oldTreeIter = new EmptyTreeIterator();
ObjectReader reader = repository.newObjectReader();
AbstractTreeIterator newTreeIter = new CanonicalTreeParser(null, reader, firstCommit.getTree());
List<DiffEntry> diffEntries = df.scan(oldTreeIter, newTreeIter);
...