LSP4J MCP

JDTLS must be installed and available as a command on your PATH. On macOS use Homebrew; on Linux download from the Eclipse JDT Language Server releases page.

# macOS
brew install jdtls

# Verify
jdtls --version

LSP4J MCP is not published to Maven Central or npm; build it from source using Maven. The resulting JAR will be in the target directory.

git clone https://github.com/stephanj/LSP4J-MCP.git
cd LSP4J-MCP
mvn clean package

Run the server directly against your Java project to confirm it starts and JDTLS initializes correctly. Replace the path arguments with your actual project path and JDTLS command.

java -jar target/lsp4j-mcp-1.0.0-SNAPSHOT.jar /path/to/your/java/project jdtls

# Or use the convenience script
./run.sh /path/to/your/java/project

Create or edit your .mcp.json file in the project root (for Claude Code) or claude_desktop_config.json (for Claude Desktop). Set LOG_FILE to redirect verbose JDTLS output away from MCP stdio.

{
  "mcpServers": {
    "java-lsp": {
      "command": "java",
      "args": ["-jar", "/absolute/path/to/LSP4J-MCP/target/lsp4j-mcp-1.0.0-SNAPSHOT.jar",
               "/absolute/path/to/your/java/project", "jdtls"],
      "env": {
        "LOG_FILE": "/tmp/lsp4j-mcp.log"
      }
    }
  }
}

Ask your AI assistant to find class definitions, list method references, or discover interface implementations. The server delegates to JDTLS and returns compiler-accurate results based on the actual project classpath.