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

FAQ from Pure Java 21 MCP Server

What are the prerequisites for Pure Java 21 MCP Server?

Java 21 SDK and the Gson library JAR (e.g., gson-2.10.