palantir-java-format-action

GitHub Action that checks Java code formatting using palantir-java-format native binary.

No Java, Maven, or Gradle required — downloads a native binary from Maven Central.

Usage

- uses: actions/checkout@v4

- uses: abashev/palantir-java-format-action@v2
  with:
    version: '2.96.0'

Inputs

Input	Required	Default	Description
version	yes	2.96.0	Version of palantir-java-format native binary
mode	no	changed	changed — only files from PR or push; all — every .java file in repo

How mode: changed works

• Pull request — gets the list of changed files from the PR via gh pr diff
• Push — gets files changed between before and after commits in the push
• Other events — falls back to checking all .java files

Behaviour

• If all files are formatted correctly → passes ✅
• If any file has formatting issues → lists unformatted files and fails ❌

When the check fails, fix locally with:

palantir-java-format --palantir --replace <files>

Excluding files

Both the action and the pre-commit hook read an optional .palantir-java-format-exclude file from the repository root. Every non-empty, non-comment line is a git pathspec (relative to the repo root); any Java file matching a pattern is skipped. If the file is absent, nothing is excluded.

# .palantir-java-format-exclude

# Standalone jbang scripts — the formatter would rewrite their //DEPS directives into comments
samples/**

# Generated sources
**/build/generated/**

Notes:

• Patterns use git pathspec syntax, so both samples/** and samples match everything under samples/.
• Lines starting with # are comments; blank lines are ignored.
• This file is the single source of exclusions — it is shared by the action and the hook, so there is no separate action input to configure.

Recommended setup

on:
  pull_request:
  push:
    branches: [main]

jobs:
  format:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - uses: abashev/palantir-java-format-action@v2
        with:
          version: '2.96.0'
          mode: ${{ github.event_name == 'push' && 'all' || 'changed' }}

Git pre-commit hook

You can also use the same formatter as a local git hook to catch formatting issues before they reach CI.

Copy pre-commit to your project:

cp pre-commit .git/hooks/pre-commit
# or with a custom hooks directory
cp pre-commit .githooks/pre-commit
git config core.hooksPath .githooks

The hook automatically downloads and caches the native binary on first run, then checks only staged .java files on each commit. It also honours the same .palantir-java-format-exclude file as the action.

Supported platforms

• Linux x86_64
• Linux aarch64
• macOS aarch64 (Apple Silicon)