MCP Server Connector— Quick Build Guide with Java and Multi-Language Support

[vishalmysore]

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🔌 MCP Connector: Plug Your Java Server into Any Client — Effortlessly!

🧠 What I Built

I built a pure Java connector for the Model Context Protocol (MCP), which acts as a lightweight passthrough bridge between MCP-compatible AI agents (like Claude Desktop, VS Code Extensions, etc.) and backend MCP Servers written in any language — including Java, Spring Boot, Python, Node.js, or even shell scripts.

This connector listens on stdin, forwards JSON-RPC messages to a backend server over HTTP, and writes back to stdout — making it a seamless drop-in replacement for agent config.

✅ Bonus: I also created a dynamic illustration (shown above) showing how different MCP servers can plug into a unified agent experience using connectors — just like USB for AI tools!

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🚀 Why Build It?

Most examples around MCP connectors were in JavaScript. As someone who primarily builds AI-enhanced robots and microservices in Java (e.g., Spring Boot), I needed a reliable way to:

• Plug Java-based MCP Servers into Claude without rewriting in Node.js
• Enable protocol bridging for any backend with JSON-RPC 2.0 over HTTP
• Standardize agent configuration in Claude Desktop with language-agnostic bridges

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🔧 How It Works

The connector works like a universal translator:

1. Reads JSON-RPC messages from an agent (via stdin)
2. POSTs them to a target MCP server via HTTP
3. Returns the response to the AI agent via stdout

Claude Desktop Configuration Example

"routeplanningagent": {
  "command": "java",
  "args": [
    "-jar",
    "/path/to/mcp-connector-full.jar",
    "http://localhost:8080"
  ],
  "timeout": 30000
}

🛠️ Available Connector Types
In addition to the Java implementation, the following connectors are supported for different environments:

"customerserviceagent": {
  "command": "node",
  "args": ["/work/a2ajava.cjs", "http://localhost:7860"],
  "timeout": 30000
}

✅ Python Connector (Work-in-Progress)

"pythonagent": {
  "command": "python",
  "args": ["mcp_connector.py", "http://localhost:8080"],
  "timeout": 30000
}

✅ Shell Script Connector (WIP)

"shellagent": {
  "command": "bash",
  "args": ["mcp_connector.sh", "http://localhost:8080"],
  "timeout": 30000
}

💥 Challenges Faced
Handling empty JSON-RPC responses (like notifications) in both Java and Node.js
Ensuring line-buffered stdout communication to satisfy the Claude agent stream expectations
Packaging a self-contained shaded JAR for Java without Maven conflicts
Visualizing the architecture in a way that's developer-friendly and intuitive

📚 What I Learned
The importance of stdin/stdout protocol adherence in MCP design
How to leverage Java Process APIs and System.in/out to simulate agent pipes
Cross-language communication patterns using JSON-RPC 2.0
The value of having pluggable connectors across diverse tech stacks

Relevant Links

Source - Here
Blog Here