JGit如何查文件相關的每一次diff，“git log -p”命令

需求說明

JGit 提供了一個Git 命令的Java API，你可以在項目中使用git，像命令行一樣方便操作，查詢git項目。JGit項目目前由Eclipse維護，JGit主頁https://www.eclipse.org/jgit/
我想查詢一個git項目,他的某一個文件的歷史改動記錄，git命令中用
git log -p [file]
即可很容易實現，jgit中的LogCommand裏面有很多參數可以設置命令，但是-p這個，無法實現，所以只能用DiffFormatter來依次對比該文件提交的所有歷史版本不同

public static void test() {
    try {

        File gitWorkDir = new File("/home/test/GITTEST/");
        Git git = null;
        git = Git.open(gitWorkDir);
        Repository repo = git.getRepository();

        LogCommand log = git.log();
        log.addPath("lakmal.txt");

        ObjectId lastCommitId = repo.resolve(Constants.HEAD);
        RevWalk rw = new RevWalk(repo);
        RevCommit parent = rw.parseCommit(lastCommitId);

        rw.sort(RevSort.COMMIT_TIME_DESC);
        rw.markStart(parent);

        log.setMaxCount(3);
        Iterable<RevCommit> logMsgs = log.call();
        for (RevCommit commit : logMsgs) {
            System.out.println("\n\n\n\n\n\n\n\n\n\n----------------------------------------");
            System.out.println("commit    " + commit);
            System.out.println("commit.toObjectId()    " + commit.toObjectId());
            System.out.println(" commit.getAuthorIdent().getName()         " + commit.getAuthorIdent().getName());
            System.out.println("" + commit.getAuthorIdent().getWhen());
            System.out.println(" commit.getFullMessage())--- " + commit.getFullMessage());
            System.out.println("---DIF STARTING ------------------------");

            //RevTree tree = commit.getTree();DisabledOutputStream.INSTANCE

            ByteArrayOutputStream out = new ByteArrayOutputStream();

            DiffFormatter df = new DiffFormatter(out);  // DisabledOutputStream.INSTANCE
            df.setRepository(repo);
            df.setDiffComparator(RawTextComparator.DEFAULT);
            df.setDetectRenames(true);

            //df.format(parent.getTree(), commit.getTree());
            List<DiffEntry> diffs = df.scan(commit.getTree(), commit.getParent(0).getTree()); //df.scan(parent.getTree(), commit.getTree());
            for (DiffEntry diff : diffs) {
                //System.out.println(getCommitMessage());
//df.format(diff);
                System.out.println("changeType=" + diff.getChangeType().name()
                        + " \n newMode=" + diff.getNewMode().getBits()
                        + " \nnewPath=" + diff.getNewPath()
                        + " \nold path " + diff.getOldPath()
                        + " \nHash code " + diff.hashCode()
                        + " \nString  " + diff.toString()
                        + " \nchange " + diff.getChangeType().toString()
                );

                df.format(diff);
                String diffText = out.toString("UTF-8");
                System.out.println(diffText);
            }
            df.release();
            out.close();
            parent = commit;

        }

    } catch (Exception e) {
        System.out.println("no head exception : " + e);
    }
}