如何在JGit中「貓」一個文件？

Question

後來我一直在尋找embeddable distributed version control system in Java, ，我想我已經在JGit中找到它了，它是純粹的git實現。 但是，示例代碼或教程沒有多少內容。

如何使用JGit檢索某個文件的HEAD版本（就像svn cat或hg cat）？

我想這涉及到一些rev-tree-walking，並且正在尋找代碼示例。

Answer 1

不幸的是，Thilo的答案不適用於最新的JGit API。這裏是我找到的解決方案：

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) 

我希望它更簡單。

Answer 2

有一些信息在JGit Tutorial（但也沒有真正的幫助也沒有完整，可能已經過時，因爲他們切換到eclipse沒有文檔可用）。

Answer 3

自己弄明白了。該API是相當低級的，但它不是太糟糕：

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 4

我已經開始編寫一個名爲gitective的庫，其中包含許多使用JGit處理Blob，提交和樹的幫助程序，並且已獲得MIT許可並可在GitHub上獲得。在頭文件的

獲取內容提交

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

分支上獲取文件的內容

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

DIFF兩個文件

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); 

更多的實用程序示例詳見README。

Answer 5

我跟着@蒂洛的和@ morisil的回答得到這個，兼容JGit 1.2.0：

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(); 

我沒有測試的Java版本，但它應該工作。它翻譯自

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

在clojure（遵循與頂部相同的設置），它工作。

Answer 6

這裏的@ morisil的回答的一個簡化版本，使用一些從@directed笑的概念，並與JGit 2.2.0測試：

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是在其他的答案中創建一個資源庫對象。