MCP Spring Boot Example with User Service

This project demonstrates how to build a simple Spring Boot API and expose it as both REST endpoints and Model Context Protocol (MCP) tools using Spring Boot and Spring AI MCP Server. The app now includes a UserService that is exposed as an MCP tool.

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Table of Contents

• Features
• Requirements
• Setup
• Running the Application
• REST API Usage
• MCP Server Usage (SSE + JSON-RPC)
• Testing
• Development Notes
• Troubleshooting

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Features

• UserService tool: get user details by user ID (REST and MCP)
• REST API endpoint for user details
• MCP server exposes user service as AI tool (usable by VS Code Copilot, etc.)
• Full test coverage with integration tests

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Requirements

• Java 17+
• Maven 3.8+
• VS Code (optional, for MCP client testing)
• REST Client extension (optional, for .http files)

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Setup

1. Clone the repository:

   git clone <your-repo-url>
   cd mcpdemo

2. Configure Git (optional):

   git config user.name "<your-username>"
   git config user.email "<your-email>"

3. Build the project:

   ./mvnw clean install

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Running the Application

Start the Spring Boot application:

./mvnw spring-boot:run

The server will start on http://localhost:8080.

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REST API Usage

You can test the user endpoint using curl, Postman, or the provided .http file.

UserService Example request:

• Get user details:

  GET http://localhost:8080/api/users/123

  Response:

  "User: 123, Name: John Doe"

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MCP Server Usage (SSE + JSON-RPC)

The MCP server uses Server-Sent Events (SSE) for session-based communication and JSON-RPC over HTTP for sending messages. This allows you to receive asynchronous responses in a browser or SSE client while sending requests via POST.

1. Create a session using the SSE endpoint

Open your browser and navigate to:

http://localhost:8080/mcp/sse

A new session will be created and you will receive a response like:

id:8a09a074-ad2d-434d-a768-8e30f25a186b
event:endpoint
data:/mcp/messages?sessionId=8a09a074-ad2d-434d-a768-8e30f25a186b

• The id is your session ID.
• The data field gives you the correct messages endpoint for this session.

2. Send JSON-RPC messages using the messages endpoint

Use a tool like Bruno, Postman, or curl to send POST requests to:

http://localhost:8080/mcp/messages?sessionId=<your-session-id>

with a JSON body. For example, to initialize:

{
  "jsonrpc": "2.0",
  "id": 0,
  "method": "initialize",
  "params": {
    "protocolVersion": "2024-11-05",
    "capabilities": {},
    "clientInfo": {
      "name": "warp",
      "version": "1.0.0"
    }
  }
}

Then send:

{
  "jsonrpc": "2.0",
  "method": "notifications/initialized"
}

You can now send tool/list or tool/invoke requests as shown below. All responses will appear in the browser window (SSE session) you opened in step 1.

Example: List available tools

{
  "jsonrpc": "2.0",
  "id": "2",
  "method": "tools/list",
  "params": {}
}

Example: Invoke a tool

{
  "jsonrpc": "2.0",
  "id": "3",
  "method": "tools/call",
  "params": {
    "name": "getUserDetailsMcp",
    "arguments": {
      "userId": "123"
    }
  }
}

Example response (will appear in SSE session)

{
  "jsonrpc": "2.0",
  "id": "3",
  "result": "User: 123, Name: John Doe"
}

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VS Code Integration

1. Open VS Code and install an MCP-compatible extension (e.g., Copilot Chat).
2. Set the MCP server URL to http://localhost:8080/mcp/sse in the extension settings.
3. Use the extension's chat or tool features to call your user tool.

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Testing

Run all tests with:

./mvnw test

All endpoints and MCP tools are covered by integration tests.

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Development Notes

• User logic is in UserService.
• REST endpoint is in UserController.
• MCP tool registration is in McpConfig.
• MCP server configuration is in src/main/resources/application.yaml.

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Troubleshooting

• SessionId error: Always include a sessionId in MCP tool/completion requests.
• Tool not visible in VS Code: Ensure the MCP server is running and the extension is pointed to the correct URL.
• Port conflicts: Change the port in application.yaml if needed.
• Logs: Enable TRACE logging in application.yaml for detailed MCP server logs.

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License

Apache 2.0