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MCP Coding Example

Demonstrates a coding agent that uses MCP (Model Context Protocol) reference servers for filesystem and git operations instead of Java-native tools.

What It Does

  1. Accepts a git-tracked project directory as a command-line argument
  2. Starts MCP filesystem and git reference servers scoped to the project
  3. Combines all MCP tools into a single coding agent
  4. Runs a bug-fix task using the MCP tools for file reading, editing, and git operations
  5. Shuts down the MCP servers automatically when complete

Code

// Use the first CLI argument as the project directory, or default to "."
Path projectDir = args.length > 0 ? Path.of(args[0]) : Path.of(".");

ChatModel model = OpenAiChatModel.builder()
    .apiKey(System.getenv("OPENAI_API_KEY"))
    .modelName("gpt-4o")
    .build();

// Start MCP filesystem and git servers (AutoCloseable)
try (McpServerLifecycle fs = McpToolFactory.filesystem(projectDir);
        McpServerLifecycle git = McpToolFactory.git(projectDir)) {

    fs.start();
    git.start();

    // Combine filesystem and git tools
    List<Object> mcpTools = new ArrayList<>();
    mcpTools.addAll(fs.tools());
    mcpTools.addAll(git.tools());

    // Build a coding agent with MCP tools
    Agent agent = Agent.builder()
        .role("Senior Software Engineer")
        .goal("Implement, debug, and refactor code with precision")
        .tools(mcpTools)
        .llm(model)
        .maxIterations(75)
        .build();

    Task task = CodingTask.fix("Find and fix any compilation errors")
        .toBuilder()
        .agent(agent)
        .build();

    EnsembleOutput output = Ensemble.run(model, task);
    System.out.println(output.getRaw());
}

Running

export OPENAI_API_KEY=sk-...
./gradlew :agentensemble-examples:runMcpCoding --args="/path/to/git/project"

If no path argument is provided, the current directory is used.

Prerequisites: Node.js must be installed (npx available on the system PATH). The MCP reference servers are installed automatically via npx --yes on first run.

Key Concepts

  • MCP servers: McpToolFactory.filesystem() and McpToolFactory.git() start the official MCP reference server subprocesses. Each exposes a standard set of tools (file read/write/search, git status/diff/commit, etc.).
  • Lifecycle management: McpServerLifecycle implements AutoCloseable. Use try-with-resources to ensure servers are shut down cleanly.
  • Tool composition: MCP tools produce standard AgentTool instances that can be freely mixed with Java-native tools in any agent's tool list.
  • CodingTask: The CodingTask.fix() convenience method provides a pre-configured task description and expected output for bug-fix workflows.

MCP Tools Available

The exact tool names are defined by the MCP reference servers. You can discover them at runtime via fs.tools() and git.tools(). Typical tools include:

Filesystem server tools

read_file, write_file, edit_file, search_files, list_directory, directory_tree, get_file_info

Git server tools

git_status, git_diff_unstaged, git_diff_staged, git_diff, git_commit, git_add, git_log, git_branch, git_create_branch, git_checkout, git_show, git_reset

See Also