open-java-format-action

GitHub Action that checks Java code formatting using the open-java-format native binary. The same check also comes as a git pre-commit hook.

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

Usage

- uses: actions/checkout@v7

- uses: openjavaformat/open-java-format-action@v2
  with:
    version: '2.98.0.4'

v2 is for open-java-format 2.98.0.2 and later, which has a single style. A workflow that pins 2.98.0.1 stays on @v1, which passes that version the --ojf flag it needs.

Inputs

Input	Required	Default	Description
version	yes	2.98.0.4	Version of the open-java-format native binary, one of those on Maven Central
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; needs that history, so check out with fetch-depth: 0
• Other events, or a push whose before commit is not in the checkout — 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 ❌

Files are checked in the open-java-format style, the formatter's only style. When the check fails, fix locally with a native binary or the runnable jar from the open-java-format releases:

open-java-format --replace <files>
# or, with Java 21 or later
java -jar open-java-format-2.98.0.4-all.jar --replace <files>

Excluding files

Both the action and the pre-commit hook read an optional .open-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.

# .open-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@v7

      - uses: openjavaformat/open-java-format-action@v2
        with:
          version: '2.98.0.4'
          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 the native binary on first run and caches it in ~/.cache/open-java-format, then checks only staged .java files on each commit. It also honours the same .open-java-format-exclude file as the action.

The hook pins its own formatter version in FORMATTER_VERSION at the top of the script — keep it in step with the version your workflow passes to the action.

Supported platforms

• Linux x86_64 (glibc)
• Linux aarch64 (glibc)
• macOS aarch64 (Apple Silicon)
• macOS x86_64 (Intel)
• Windows x86_64

There is no native binary for Windows on ARM or for musl-based Linux such as Alpine.