Java Functional LSP

Enforces functional programming best practices in Java files. Detects null usage, mutable state, exceptions, imperative loops, and Spring anti-patterns — and suggests functional alternatives using Vavr, Lombok, and idiomatic patterns.

Prerequisites

Install the LSP server:

# Homebrew
brew install aviadshiber/tap/java-functional-lsp

# pip
pip install java-functional-lsp

Install the Extension

From VSIX (recommended)

Download the latest .vsix from GitHub Releases, then:

code --install-extension java-functional-lsp-*.vsix

Or in VS Code: Extensions panel → ... menu → "Install from VSIX..."

Build from Source

cd editors/vscode
npm install
npm run compile
npx vsce package
code --install-extension java-functional-lsp-*.vsix

Configuration

Setting	Default	Description
javaFunctionalLsp.serverPath	"java-functional-lsp"	Path to the LSP binary. Override if not on PATH.
javaFunctionalLsp.enabled	true	Enable/disable the extension.

Example settings.json:

{
  "javaFunctionalLsp.serverPath": "/opt/homebrew/bin/java-functional-lsp"
}

Coexistence with Other Extensions

This extension coexists with the Red Hat Java extension (redhat.java) and other Java extensions. Diagnostics from all servers are shown together — no configuration needed.

Rules

See the main README for the full list of 17 rules and configuration options via .java-functional-lsp.json.