eclipse-jdtls-setup

name	eclipse-jdtls-setup
description	Guide for installing and configuring Eclipse JDT Language Server (JDTLS) for Java development. Use this skill when the user needs help setting up Java language support, troubleshooting JDTLS issues, or configuring their Java development environment.

Eclipse JDTLS Setup Guide

You are an expert at setting up Eclipse JDT Language Server for Java development across Windows, macOS, and Linux.

Prerequisites

• Java 21 or later must be installed. Verify with java -version.
• Set JAVA_HOME to point to your JDK installation.

Automatic Download

The launcher scripts included with this plugin automatically download Eclipse JDTLS from https://download.eclipse.org/jdtls/milestones/ if it is not already installed. The scripts:

1. Check JDTLS_HOME and common installation paths
2. If not found, detect the latest milestone version
3. Download and extract to ~/.local/share/jdtls (macOS/Linux) or %LOCALAPPDATA%\jdtls (Windows)
4. Fall back to manual instructions only if the download fails

Manual Installation (Fallback)

If auto-download fails (e.g., no internet, firewall restrictions), install manually:

macOS (Homebrew)

brew install jdtls

macOS / Linux (Manual Download)

1. Download the latest milestone from https://download.eclipse.org/jdtls/milestones/
2. Extract to a directory, for example ~/.local/share/jdtls
3. Set environment variable: export JDTLS_HOME=~/.local/share/jdtls
4. Add to your shell profile (~/.bashrc, ~/.zshrc, etc.)

Windows (Manual Download)

1. Download the latest milestone from https://download.eclipse.org/jdtls/milestones/
2. Extract to a directory, for example %LOCALAPPDATA%\jdtls
3. Set environment variable: JDTLS_HOME=%LOCALAPPDATA%\jdtls

Linux (Package Manager)

Some distributions provide JDTLS packages:

• Arch Linux: pacman -S jdtls
• Other distributions: Check your package repository for jdtls or eclipse-jdt-ls

Verifying the Installation

After installation, verify that the plugins/ directory exists inside your JDTLS installation and contains org.eclipse.equinox.launcher_*.jar.

ls $JDTLS_HOME/plugins/org.eclipse.equinox.launcher_*.jar

LSP Configuration for Copilot CLI

This plugin automatically configures JDTLS via the bundled bin/launch-jdtls bash script (macOS/Linux). The script auto-detects your platform and JDTLS location — no Python wrapper needed.

Windows users must override the config in ~/.copilot/lsp-config.json to use the PowerShell launcher:

{
  "lspServers": {
    "eclipse-jdtls": {
      "command": "powershell",
      "args": ["-ExecutionPolicy", "Bypass", "-File", "C:\\Users\\YOU\\.copilot\\state\\installed-plugins\\eclipse-jdtls\\bin\\launch-jdtls.ps1"],
      "fileExtensions": {
        ".java": "java"
      }
    }
  }
}

Troubleshooting

"Java not found"

• Ensure Java 21+ is installed: java -version
• Set JAVA_HOME environment variable to your JDK path

"Eclipse JDTLS not found"

• Set the JDTLS_HOME environment variable to the JDTLS installation directory
• Ensure the directory contains a plugins/ subdirectory with the launcher JAR

"Configuration directory not found"

• Verify that config_linux/, config_mac/, or config_win/ exists in $JDTLS_HOME
• Re-download JDTLS if these directories are missing

No completions or diagnostics

1. Ensure the project root contains pom.xml or build.gradle
2. For Maven projects, run ./mvnw dependency:resolve (or mvn dependency:resolve if no wrapper) to populate the local cache
3. For Gradle projects, run ./gradlew build (or gradle build if no wrapper) once to populate the local cache
4. Check JDTLS logs for errors

Memory issues

• Increase heap size by setting JAVA_OPTS=-Xmx2G before launching
• Large projects may need 2-4 GB of heap space