JGit教程：实现特定Commit ID的检出

import org.eclipse.jgit.api.Git;
import org.eclipse.jgit.api.errors.GitAPIException;
import org.eclipse.jgit.lib.ObjectId;
import org.eclipse.jgit.lib.Repository;
import org.eclipse.jgit.revwalk.RevCommit;
import org.eclipse.jgit.revwalk.RevWalk;

import java.io.File;
import java.io.IOException;

public class JGitCheckoutSpecificCommit {

    public static void main(String[] args) {
        String remoteRepoUri = "https://github.com/eclipse/jgit.git"; // 示例仓库URI
        File localPath = new File("jgit-local-repo"); // 本地克隆路径
        String commitIdToCheckout = "a1b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0"; // 替换为实际的提交ID

        Git git = null;
        Repository repository = null;

        try {
            // 1. 克隆仓库（如果不存在）或打开现有仓库
            if (!localPath.exists()) {
                System.out.println("克隆仓库到: " + localPath.getAbsolutePath());
                git = Git.cloneRepository()
                         .setURI(remoteRepoUri)
                         .setDirectory(localPath)
                         .call();
                System.out.println("仓库克隆完成。");
            } else {
                System.out.println("打开现有仓库: " + localPath.getAbsolutePath());
                git = Git.open(localPath);
            }
            repository = git.getRepository();

            // 2. 解析提交ID为RevCommit对象
            System.out.println("尝试检出到提交ID: " + commitIdToCheckout);
            ObjectId commitObjectId = repository.resolve(commitIdToCheckout);

            if (commitObjectId == null) {
                System.err.println("错误: 无法解析提交ID " + commitIdToCheckout + "。请确保该提交ID存在于本地仓库中。");
                return;
            }

            RevCommit revCommit;
            try (RevWalk revWalk = new RevWalk(repository)) {
                revCommit = revWalk.parseCommit(commitObjectId);
            }

            // 3. 执行检出操作
            System.out.println("正在执行检出操作...");
            git.checkout()
               .setAllPaths(true) // 确保所有文件都被更新到目标提交状态
               .setStartPoint(revCommit)
               .call();

            System.out.println("成功检出到提交ID: " + commitIdToCheckout);
            System.out.println("当前HEAD指向: " + repository.getRefDatabase().exactRef("HEAD").getTarget().getObjectId().getName());

        } catch (GitAPIException | IOException e) {
            System.err.println("JGit操作失败: " + e.getMessage());
            e.printStackTrace();
        } finally {
            if (git != null) {
                git.close(); // 关闭Git实例，释放资源
            }
            if (repository != null) {
                repository.close(); // 关闭Repository实例
            }
        }
    }
}

// 假设 repository 已经获取
ObjectId commitObjectId = repository.resolve(commitIdToCheckout);
if (commitObjectId == null) {
    // 提交ID无效或不存在于本地仓库
    System.err.println("错误: 无法解析提交ID " + commitIdToCheckout);
    return;
}

RevCommit revCommit;
try (RevWalk revWalk = new RevWalk(repository)) {
    revCommit = revWalk.parseCommit(commitObjectId);
}

git.checkout()
   .setAllPaths(true) // 确保所有文件都被更新到目标提交状态
   .setStartPoint(revCommit)
   .call();