jgit - 我如何使用 JGit 做 "git show sha1:file"

Question

我使用 JGit 在我的本地磁盘上克隆了一个裸仓库。现在，我需要读取任何给定提交 ID (SHA1) 的文件内容。我该怎么做？

Answer 1

comment of Rüdiger Herrmann in this answer包含相关提示；但是为了让复制和粘贴解决方案的 friend 更容易，我在此处提供了一个完整的自包含的 junit 测试示例代码，该代码创建文件的修订版，然后检索该修订版的内容。适用于 jGit 4.2.0。

@Test
public void test() throws IOException, GitAPIException
{
    //
    // init the git repository in a temporary directory
    //
    File repoDir = Files.createTempDirectory("jgit-test").toFile();
    Git git = Git.init().setDirectory(repoDir).call();

    //
    // add file with simple text content
    //
    String testFileName = "testFile.txt";
    File testFile = new File(repoDir, testFileName);
    writeContent(testFile, "initial content");

    git.add().addFilepattern(testFileName).call();
    RevCommit firstCommit = git.commit().setMessage("initial commit").call();

    //
    // given the "firstCommit": use its "tree" and 
    // localize the test file by its name with the help of a tree parser
    //
    Repository repository = git.getRepository();
    try (ObjectReader reader = repository.newObjectReader())
    {
        CanonicalTreeParser treeParser = new CanonicalTreeParser(null, reader, firstCommit.getTree());
        boolean haveFile = treeParser.findFile(testFileName);
        assertTrue("test file in commit", haveFile);
        assertEquals(testFileName, treeParser.getEntryPathString());
        ObjectId objectForInitialVersionOfFile = treeParser.getEntryObjectId();

        // now we have the object id of the file in the commit:
        // open and read it from the reader
        ObjectLoader oLoader = reader.open(objectForInitialVersionOfFile);
        ByteArrayOutputStream contentToBytes = new ByteArrayOutputStream();
        oLoader.copyTo(contentToBytes);
        assertEquals("initial content", new String(contentToBytes.toByteArray(), "utf-8"));
    }

    git.close();
}

// simple helper to keep the main code shorter
private void writeContent(File testFile, String content) throws IOException
{
    try (OutputStreamWriter wr = new OutputStreamWriter(new FileOutputStream(testFile), Charset.forName("utf-8")))
    {
        wr.append(content);
    }
}

编辑添加:另一个可能更好的例子在https://github.com/centic9/jgit-cookbook/blob/master/src/main/java/org/dstadler/jgit/api/ReadFileFromCommit.java