Java Checkstyle

Java Checkstyle / Spotless

OpenMetadata enforces Java formatting via the Spotless Maven plugin. Every CI build runs mvn spotless:check and fails the PR if any file is not formatted. This skill keeps the fix on a single, consistent command so reviewers never have to ask for it manually again.

When to activate

• The user asks to "fix checkstyle", "fix Java formatting", "apply spotless", "run spotless", "format Java", or similar.
• CI posts a Java checkstyle failed / Fix Java checkstyle comment on a PR (the project's bot phrases the instruction as "Please run mvn spotless:apply in the root of your repository and commit the changes to this PR").
• After you have finished authoring or editing any .java files — before opening a PR or pushing a commit that touches Java.

Arguments

• No arguments: run mvn spotless:apply at the repo root across all modules.
• -pl <module>: scope to a single Maven module (e.g. -pl openmetadata-service). Useful when only one module changed and you want a faster run.
• --check: run mvn spotless:check instead of apply. Use to confirm the tree is clean without touching files (e.g. to verify before push).

Process

Step 1: Run Spotless

From the repo root:

mvn spotless:apply                 # default — formats everything
# or
mvn -pl <module> spotless:apply    # scoped to one module
# or
mvn spotless:check                 # verify only, don't write

Spotless is fast (seconds, no compilation). If it fails with a plugin error (not a formatting diff), surface the error and stop — do not try to hand-edit formatting around the failure.

Step 2: Check what changed

git status --short
git diff --stat

Expect reformatting in .java files only. If Spotless touches pom.xml or other non-Java files, that's also fine — Spotless is configured for those too in this repo.

Step 3: Commit

Do not fold the reformat into an unrelated commit. If the user asked you to commit, follow their preference (fold into the in-progress commit, or make a separate one). Otherwise, when you are confident the change is a purely mechanical formatting reformat, you may commit it on its own as a Fix Java checkstyle commit — this matches the repo's existing history for bot-triggered formatting-only commits. If you are unsure whether the diff is purely mechanical, do NOT auto-commit: surface the changed-file list and let the user decide.

Notes

• Spotless config lives in the root pom.xml (spotless-maven-plugin section) — googleJavaFormat + removeUnusedImports. Do not redefine formatting rules inline in source files.
• If Spotless keeps rewriting a change you just made, re-read the config — Spotless is the source of truth, not the IDE.
• CI enforcement lives in .github/workflows/java-checkstyle.yml: the java-checkstyle job runs mvn spotless:apply and fails (git diff-files) if the tree was not already formatted, posting the "Please run mvn spotless:apply" comment.

Out of scope

• UI / TypeScript formatting — use the ui-checkstyle skill (ESLint + Prettier + organize-imports); this skill is Java-only.
• Python formatting — use make py_format (ruff lint-fix + format; see ingestion/Makefile). (Note: this is ruff, not black/isort/pycln.)