Question

前段时间我正在寻找一个embeddable distributed version control system in Java，我想我已经在JGit中找到了它，它是git的纯Java实现。但是，示例代码或教程的方式并不多。

如何使用JGit检索某个文件的HEAD版本（就像svn cat或hg cat那样）？

我想这涉及一些转树走路，我正在寻找代码示例。

Answer 1

不幸的是，Thilo的答案不适用于最新的JGit API。这是我找到的解决方案：

File repoDir = new File("test-git");
// open the repository
Repository repository = new Repository(repoDir);
// find the HEAD
ObjectId lastCommitId = repository.resolve(Constants.HEAD);
// now we have to get the commit
RevWalk revWalk = new RevWalk(repository);
RevCommit commit = revWalk.parseCommit(lastCommitId);
// and using commit's tree find the path
RevTree tree = commit.getTree();
TreeWalk treeWalk = new TreeWalk(repository);
treeWalk.addTree(tree);
treeWalk.setRecursive(true);
treeWalk.setFilter(PathFilter.create(path));
if (!treeWalk.next()) {
  return null;
}
ObjectId objectId = treeWalk.getObjectId(0);
ObjectLoader loader = repository.open(objectId);

// and then one can use either
InputStream in = loader.openStream()
// or
loader.copyTo(out)

我希望它更简单。

Answer 2

这是@ morisil答案的简单版本，使用@directed笑的一些概念并使用JGit 2.2.0进行测试：

private String fetchBlob(String revSpec, String path) throws MissingObjectException, IncorrectObjectTypeException,
        IOException {

    // Resolve the revision specification
    final ObjectId id = this.repo.resolve(revSpec);

    // Makes it simpler to release the allocated resources in one go
    ObjectReader reader = this.repo.newObjectReader();

    try {
        // Get the commit object for that revision
        RevWalk walk = new RevWalk(reader);
        RevCommit commit = walk.parseCommit(id);

        // Get the revision's file tree
        RevTree tree = commit.getTree();
        // .. and narrow it down to the single file's path
        TreeWalk treewalk = TreeWalk.forPath(reader, path, tree);

        if (treewalk != null) {
            // use the blob id to read the file's data
            byte[] data = reader.open(treewalk.getObjectId(0)).getBytes();
            return new String(data, "utf-8");
        } else {
            return "";
        }
    } finally {
        reader.release();
    }
}

repo是在其他答案中创建的Repository对象。

Answer 3

我跟着@ Thilo和@ morisil的回答得到了这个，与JGit 1.2.0兼容：

File repoDir = new File("test-git/.git");
// open the repository
Repository repo = new Repository(repoDir);
// find the HEAD
Commit head = repo.mapCommit(Constants.HEAD);
// retrieve the tree in HEAD
Tree tree = head.getTree();

// 1.2.0 api version here
// find a file (as a TreeEntry, which contains the blob object id)
TreeWalk treewalk = TreeWalk.forPath(repo, "b/test.txt", tree);
// use the blob id to read the file's data
byte[] data = repo.open(treewalk.getObjectId(0)).getBytes();

我没有测试Java版本，但它应该可以工作。它翻译自

(.getBytes (.open repo (.getObjectId (TreeWalk/forPath repo "b/test.txt" tree) 0)))

在clojure中（遵循与顶部相同的设置），这确实有效。

Answer 4

自己想出来。 API非常低级，但它并不太糟糕：

File repoDir = new File("test-git/.git");
// open the repository
Repository repo = new Repository(repoDir);
// find the HEAD
Commit head = repo.mapCommit(Constants.HEAD);
// retrieve the tree in HEAD
Tree tree = head.getTree();
// find a file (as a TreeEntry, which contains the blob object id)
TreeEntry entry = tree.findBlobMember("b/test.txt");
// use the blob id to read the file's data
byte[] data = repo.openBlob(entry.getId()).getBytes();

Answer 5

我已经开始编写一个名为gitective的库，其中包含许多帮助程序，用于使用JGit处理blob，提交和树，并且已获得MIT许可并可在GitHub上使用。

在HEAD提交中获取文件内容

Repository repo = new FileRepository("/repos/project/.git");
String content = BlobUtils.getHeadContent(repo, "src/Buffer.java");

获取分支上的文件内容

Repository repo = new FileRepository("/repos/project/.git");
String content = BlobUtils.getContent(repo, "master", "src/Buffer.java");

区分两个文件

Repository repo = new FileRepository("/repos/project/.git");
ObjectId current = BlobUtils.getId(repo, "master", "Main.java");
ObjectId previous = BlobUtils.getId(repo, "master~1", "Main.java");
Collection<Edit> edit = BlobUtils.diff(repo, previous, current);

README中详细介绍了所提供实用程序的更多示例。

Answer 6

JGit Tutorial有一些信息（但这也不是真正有用也不完整，可能已经过时了，因为他们切换到eclipse尚未提供任何文档。）

Answer 7

您可以按如下方式阅读给定文件路径的内容。请注意，如果在给定树中找不到路径，TreeWalk可以 null 。所以它需要一些特定的处理。

public String readFile(RevCommit commit, String filepath) throws IOException {
    try (TreeWalk walk = TreeWalk.forPath(repo, filepath, commit.getTree())) {
        if (walk != null) {
            byte[] bytes = repo.open(walk.getObjectId(0)).getBytes();
            return new String(bytes, StandardCharsets.UTF_8);
        } else {
            throw new IllegalArgumentException("No path found.");
        }
    }
}

例如：

ObjectId head = repo.resolve(Constants.HEAD);
RevCommit last = repo.parseCommit(head);
readFile(last, "docs/README.md")

这个答案是用JGit 4.8.0编写的。

如何在JGit中“捕捉”文件？

7 个答案: