Pure Java 21 MCP Server

What is Pure Java 21 MCP Server?

An implementation of a Model Context Protocol (MCP) server written in pure Java 21, built from scratch without external MCP-specific SDKs. It uses STDIO transport with Content-Length framed JSON-RPC messages and is intended for developers who need a lightweight, Java-native MCP server.

How to use Pure Java 21 MCP Server?

Ensure Java 21 and the Gson library JAR are available. Place the Gson JAR in a lib directory, compile all Java sources into bin, then run the server using java -cp "bin:lib/gson-2.10.1.jar" io.modelcontextprotocol.server.Main. The server listens for JSON-RPC messages on standard input.

Key features of Pure Java 21 MCP Server?

• Pure Java 21 implementation with no external MCP SDKs
• STDIO transport with Content-Length header framing
• Implements initialize, initialized, shutdown, and exit lifecycle
• Provides a single tool: echoTool (echoes a message)
• Logging to file (mcp-server.log) and console

Use cases of Pure Java 21 MCP Server?

• Testing MCP client-server communication over STDIO
• Demonstrating tool-calling with a simple echo tool
• Validating MCP protocol implementation in Java
• Lightweight integration into Java applications requiring MCP