how-to-build-mcp-server-in-java

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This guide provides a comprehensive overview of building a Model Context Protocol (MCP) server using Java, enabling AI assistants to access presentation data.

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How to Build MCP Server in Java

A comprehensive guide to building a Model Context Protocol (MCP) server using Java. This project demonstrates how to create a Java-based MCP server that provides presentation data through tools that can be consumed by AI assistants like Claude.

Table of Contents

Overview

This project implements a Java-based MCP (Model Context Protocol) server that exposes presentation data through a standardized interface. The server uses the io.modelcontextprotocol.sdk library to handle MCP communication and provides tools that AI assistants can call to retrieve information about Java presentations.

What is MCP?

The Model Context Protocol (MCP) is an open standard that enables AI assistants to securely connect to external data sources and tools. It provides a standardized way for applications to expose their functionality to AI systems.

Prerequisites

  • Java 21 or higher - This project uses Java 21 features
  • Maven 3.6+ - For dependency management and building
  • Node.js and npm - Required for MCP Inspector testing (optional)
  • Claude Desktop - For connecting the server to Claude (optional)

Project Structure

how-to-build-mcp-server-in-java/
ā”œā”€ā”€ src/main/java/
ā”‚   ā””ā”€ā”€ dev/
ā”‚       ā”œā”€ā”€ Main.java                    # Main server entry point
ā”‚       ā””ā”€ā”€ aditya/
ā”‚           ā”œā”€ā”€ Presentation.java        # Data model for presentations
ā”‚           ā””ā”€ā”€ PresentationTools.java   # Business logic for managing presentations
ā”œā”€ā”€ pom.xml                             # Maven configuration
ā”œā”€ā”€ README.md                           # This documentation
ā””ā”€ā”€ .gitignore                         # Git ignore rules

Getting Started

1. Clone the Repository

git clone <your-repository-url>
cd how-to-build-mcp-server-in-java

2. Build the Project

mvn clean compile

3. Verify Dependencies

The project uses the following key dependencies:

  • io.modelcontextprotocol.sdk:mcp - MCP SDK for Java
  • org.slf4j:slf4j-api and org.slf4j:slf4j-simple - Logging

Running the Server

Method 1: Using Maven

mvn exec:java -Dexec.mainClass="dev.Main"

Method 2: Using Java directly

# First compile
mvn compile

# Then run
java -cp target/classes:target/dependency/* dev.Main

Method 3: Create executable JAR

mvn package
java -jar target/how-to-build-mcp-server-in-java-1.0-SNAPSHOT.jar

Testing with MCP Inspector

The MCP Inspector is a debugging tool that allows you to test your MCP server interactively.

1. Install MCP Inspector

npm install -g @modelcontextprotocol/inspector

2. Run the Inspector

npx @modelcontextprotocol/inspector java -cp target/classes:$(mvn dependency:build-classpath -Dmdep.outputFile=/dev/stdout -q) dev.Main

Or if you have a compiled JAR:

npx @modelcontextprotocol/inspector java -jar target/how-to-build-mcp-server-in-java-1.0-SNAPSHOT.jar

3. Using the Inspector

  1. The inspector will open in your browser
  2. You'll see the server capabilities and available tools
  3. You can test the get_presentations tool by clicking on it
  4. The inspector will show the JSON response from your server

Connecting with Claude Desktop

To use this MCP server with Claude Desktop, you need to configure it in Claude's settings.

1. Locate Claude Desktop Configuration

On macOS:

~/Library/Application Support/Claude/claude_desktop_config.json

On Windows:

%APPDATA%\Claude\claude_desktop_config.json

2. Add Server Configuration

Add your Java MCP server to the configuration file:

{
  "mcpServers": {
    "java-presentations": {
      "command": "java",
      "args": [
        "-cp",
        "/path/to/your/project/target/classes:/path/to/your/project/target/dependency/*",
        "dev.Main"
      ],
      "cwd": "/path/to/your/project"
    }
  }
}

Alternative with JAR file:

{
  "mcpServers": {
    "java-presentations": {
      "command": "java",
      "args": [
        "-jar",
        "/path/to/your/project/target/how-to-build-mcp-server-in-java-1.0-SNAPSHOT.jar"
      ]
    }
  }
}

3. Restart Claude Desktop

After saving the configuration, restart Claude Desktop. You should now be able to ask Claude about presentations, and it will use your Java MCP server to fetch the data.

4. Test the Connection

Try asking Claude:

  • "What presentations are available?"
  • "Show me all Java presentations from 2025"
  • "List the presentation URLs"

Understanding the Code

Main.java

The main class sets up the MCP server with:

  • Transport Layer: Uses stdio for communication
  • Server Info: Defines server name and version
  • Capabilities: Declares what the server can do (tools, logging)
  • Tool Registration: Registers available tools with their implementations

Presentation.java

A simple record class representing a presentation with:

  • title: The presentation title
  • url: Link to the presentation
  • year: Year the presentation was given

PresentationTools.java

Contains the business logic for managing presentations:

  • Initializes sample presentation data
  • Provides methods to retrieve presentations
  • Supports filtering by year
  • Can convert presentations to different formats

Available Tools

get_presentations

Description: Retrieves a list of all available Java presentations

Parameters:

  • operation (string): Operation type (currently not used in implementation)

Returns: List of presentations with title, URL, and year information

Example Response:

Presentation[title=Java 24 Launch - Live from JavaOne 2025, url=https://www.youtube.com/watch?v=mk_2MIWxLI0, year=2025]
Presentation[title=Java Turns 30 - Live from JavaOne 2025, url=https://www.youtube.com/watch?v=GwR7Gvi80Xo, year=2025]
...

Customization

Adding New Tools

To add a new tool to your MCP server:

  1. Define the tool schema in JSON format
  2. Create the tool specification with name, description, and schema
  3. Implement the tool logic in the handler function
  4. Register the tool with the server builder

Example:

var newToolSpec = new McpServerFeatures.SyncToolSpecification(
    new McpSchema.Tool("my_new_tool", "Description of what it does", schema),
    (exchange, arguments) -> {
        // Your tool implementation here
        return new McpSchema.CallToolResult(contents, false);
    }
);

Modifying Data

To change the presentation data:

  1. Edit the constructor in PresentationTools.java
  2. Add, remove, or modify the Presentation objects
  3. Rebuild and restart the server

Adding Resources or Prompts

The MCP SDK also supports resources and prompts. You can add these using the server builder:

.resources(resourceSpecification)
.prompts(promptSpecification)

Troubleshooting

Common Issues

  1. "Class not found" errors: Ensure all dependencies are in the classpath
  2. Port already in use: The server uses stdio, so port conflicts shouldn't occur
  3. JSON parsing errors: Check that your tool schemas are valid JSON
  4. Claude Desktop not connecting: Verify the configuration file path and syntax

Debug Logging

The project uses SLF4J for logging. To see debug output, you can adjust the logging level or add more log statements.

Dependency Issues

If you encounter dependency resolution problems:

mvn dependency:tree
mvn clean install -U

Next Steps

  • Add more sophisticated tools with complex parameters
  • Implement resource endpoints for serving files or data
  • Add prompt templates for common AI interactions
  • Create tools that interact with external APIs or databases
  • Add authentication and security features

Contributing

Feel free to contribute to this project by:

  • Adding new example tools
  • Improving documentation
  • Fixing bugs or issues
  • Adding tests

Resources