jons-mcp-java

MCP server providing Java development capabilities through Eclipse JDT.LS.

Requirements

Python 3.10+
Java 21+ (brew install openjdk@21)
Eclipse JDT.LS (brew install jdtls)

Installation

cd /path/to/jons-mcp-java
uv sync

Usage with Claude Code

Add the MCP server to Claude Code:

claude mcp add jons-mcp-java -- uv run --project /path/to/jons-mcp-java jons-mcp-java

Replace /path/to/jons-mcp-java with the actual path to this repository.

To set the workspace root (defaults to current directory):

claude mcp add jons-mcp-java -e JONS_MCP_JAVA_WORKSPACE=/path/to/workspace -- uv run --project /path/to/jons-mcp-java jons-mcp-java

If your project uses a specific Java version (e.g., via devbox), set JAVA_HOME:

claude mcp add jons-mcp-java \
  -e JAVA_HOME=/opt/homebrew/opt/openjdk@21/libexec/openjdk.jdk/Contents/Home \
  -e JONS_MCP_JAVA_WORKSPACE=/path/to/workspace \
  -- uv run --project /path/to/jons-mcp-java jons-mcp-java

Available Tools

Tool	Description
`definition`	Go to symbol definition
`references`	Find all references to a symbol
`implementation`	Find implementations of interfaces/abstract methods
`type_definition`	Go to type definition
`document_symbols`	List all symbols in a file
`workspace_symbols`	Search for symbols across the workspace
`diagnostics`	Get errors and warnings
`hover`	Get Javadoc and type information

Environment Variables

Variable	Default	Description
`JONS_MCP_JAVA_WORKSPACE`	Current directory	Root workspace for Java projects
`JDTLS_HOME`	Auto-detect	JDT.LS installation directory
`JAVA_HOME`	Auto-detect	Java 21+ installation

Features

Multi-project support: Automatically discovers Gradle projects in mono-repos
Lazy initialization: JDT.LS instances start on-demand per project
LRU eviction: Manages memory by limiting active instances (default: 3)
Concurrent protection: Handles parallel requests safely