Java JAR MCP Server

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An npm package that provides MCP (Model Context Protocol) server functionality for Java Maven projects. This server enables AI assistants to access Java class definitions from Maven dependencies, solving the limitation where Cursor and other VSCode-based IDEs cannot automatically read jar file classes.

Features

• Class Definition Lookup: Find Java class definitions from Maven dependencies

• Dependency Listing: List all Maven dependencies for a project

• JAR Class Search: Search for classes within JAR files using patterns

Related MCP server: CodeAtlas MCP Server

Installation

Prerequisites

• Node.js 18+

• Maven installed (for Maven projects)

Using via npx

{
  "mcpServers": {
    "java-jar-mcp": {
      "command": "npx",
      "args": ["-y", "@biggerball/java-jar-mcp@latest"],
      "env": {
        "MAVEN_REPO_PATH": "/Users/username/.m2/repository"
      }
    }
  }
}

Usage

After configuration, the MCP server will automatically start and provide the following tools to AI assistants:

Available MCP Tools

find_class_definition

Find the definition of a Java class from Maven dependencies.

Parameters:

• className (string, required): Fully qualified class name (e.g., java.util.ArrayList)

• pomPath (string, required): Path to pom.xml file (e.g., "/path/to/project/pom.xml")

Returns: Class definition with source code (if available), methods, and fields

Example:

{
  "className": "com.alibaba.fastjson2.filter.BeforeFilter",
  "pomPath": "/path/to/project/pom.xml"
}

list_project_dependencies

List all Maven dependencies for a project.

Parameters:

• pomPath (string, required): Path to pom.xml file (e.g., "/path/to/project/pom.xml")

Returns: List of dependencies with JAR file paths

search_classes_in_jar

Search for classes matching a pattern in a JAR file.

Parameters:

• jarPath (string): Path to the JAR file

• searchPattern (string): Search pattern (supports wildcards * and ?)

Returns: List of matching class names

Support & Donation

If you find this project helpful and would like to support its development, I'd be grateful if you could buy me a coffee! ☕

Your support helps me continue improving this project and creating more useful tools for the developer community.

If you enjoy using this project, your support would mean a lot to me. Thank you! 🙏

Local Development Installation

1. Clone the repository

2. Install dependencies and build:

   npm install
   npm run build

3. Use local path in MCP configuration:

   {
     "mcpServers": {
       "java-jar-mcp": {
         "command": "node",
         "args": ["/path/to/java-jar-mcp/dist/index.js"],
         "env": {
           "MAVEN_REPO_PATH": "/Users/username/.m2/repository"
         }
       }
     }
   }

How It Works

The MCP server works through the following steps:

1. Parse pom.xml: Read and parse the Maven project's pom.xml file

2. Locate JAR files: Find corresponding JAR files in the local Maven repository based on Maven coordinates

3. Extract class definitions: Extract Java class definition information from JAR files

Development

Project Structure

java-jar-mcp/
├── src/
│   ├── index.ts         # MCP server entry point
│   ├── mavenParser.ts   # pom.xml parsing
│   ├── jarLocator.ts    # JAR file location
│   ├── classExtractor.ts # Class definition extraction
│   ├── tools.ts         # MCP tool implementations
│   └── cache.ts         # LRU cache implementation
└── dist/                # Compiled MCP server

Building

# Build MCP server
npm run build

# Watch mode build
npm run watch

Testing

npm test

Future Improvements

• Support for Gradle projects

• Enhanced Maven property resolution

• Automatic multi-module project detection and dependency merging

License

MIT