Quarkus MCP Server

Build MCP servers with Java 21, Quarkus, and HTTP SSE transport.

Stack

• Java 21 with Quarkus Framework
• MCP Server Extension: mcp-server-sse
• CDI for dependency injection
• MCP Endpoint: http://localhost:8080/mcp/sse

Quick Start

quarkus create app --no-code -x rest-client-jackson,qute,mcp-server-sse your-domain-mcp-server

Structure

• Use standard Java naming conventions (PascalCase classes, camelCase methods)
• Organize in packages: model, repository, service, mcp
• Use Record types for immutable data models
• State management for immutable data must be managed by repository layer
• Add Javadoc for public methods

MCP Tools

• Must be public methods in @ApplicationScoped CDI beans
• Use @Tool(name="tool_name", description="clear description")
• Never return null - return error messages instead
• Always validate parameters and handle errors gracefully

Architecture

• Separate concerns: MCP tools → Service layer → Repository
• Use @Inject for dependency injection
• Make data operations thread-safe
• Use Optional<T> to avoid null pointer exceptions

Common Issues

• Don't put business logic in MCP tools (use service layer)
• Don't throw exceptions from tools (return error strings)
• Don't forget to validate input parameters
• Test with edge cases (null, empty inputs)