fe-code-style

Development

Fix FE (Java) code style issues using Checkstyle

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Source SKILL.md: https://github.com/apache/doris/blob/HEAD/.claude/skills/fe-code-style/SKILL.md

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What I do

Diagnose and fix Java code style issues in the FE module using the project's Checkstyle configuration.

When to use me

Before committing FE Java code changes
When FE build fails due to checkstyle violations
When you need to understand FE style rules

Procedure

Step 1: Run checkstyle

Checkstyle is integrated into the Maven build and runs automatically during mvn validate. To check style only (without full compilation):

cd fe && mvn checkstyle:check -pl fe-core

Or as part of the normal build:

./build.sh --fe -j${DORIS_PARALLELISM}

If checkstyle fails, the build will fail with error messages showing the file, line number, and rule violated.

Step 2: Interpret violations

Checkstyle output looks like:

[ERROR] src/main/java/.../Foo.java:[42:5] (imports) UnusedImports: Unused import - java.util.List.
[ERROR] src/main/java/.../Bar.java:[10] (header) RegexpHeader: Line does not match expected header line...

Each error shows: [file]:[line:col] (category) RuleName: description.

Step 3: Fix common violations

Violation	Fix
`RegexpHeader`	Add/fix Apache License header at file top
`UnusedImports`	Remove unused import statements
`LineLength` (>120 chars)	Break long lines
`IllegalImport` (shaded classes)	Use the non-shaded equivalent (see `import-control.xml`)
`FileTabCharacter`	Replace tabs with spaces
`NewlineAtEndOfFile`	Ensure file ends with a newline
`MergeConflictMarker`	Resolve git merge conflicts

Step 4: Verify fix

After fixing, re-run checkstyle to confirm:

cd fe && mvn checkstyle:check -pl fe-core

Key Configuration

File	Purpose
`fe/check/checkstyle/checkstyle.xml`	Main rules (license header, line length 120, encoding, imports)
`fe/check/checkstyle/suppressions.xml`	Rule exclusions (test files, nereids, large files)
`fe/check/checkstyle/import-control.xml`	Import restrictions (no shaded classes, no old logging APIs, no Lombok in nereids)
`fe/check/checkstyle/checkstyle-apache-header.txt`	Apache License 2.0 header template
`build-support/IntelliJ-code-format.xml`	IntelliJ formatter scheme (120 col, import organization)

Suppression Rules

Some files/packages have relaxed rules (see suppressions.xml):

Test files: Javadoc rules suppressed
Non-nereids code: Some strict rules suppressed
Specific large files: Individual suppressions

Excluded Code

The following are excluded from checkstyle (see fe/pom.xml):

**/apache/doris/thrift/**/* (generated Thrift code)
**/apache/parquet/**/* (generated Parquet code)

Import Restrictions (key rules from import-control.xml)

No shaded imports: Do not use org.apache.doris.thirdparty.* directly
No old logging: Do not use org.apache.commons.logging or java.util.logging
No SimpleDateFormat: Use java.time APIs instead
No Lombok in nereids: lombok is disallowed in org.apache.doris.nereids package

Troubleshooting

Problem	Solution
Build fails on `validate` phase	Run `mvn checkstyle:check -pl fe-core` to see specific violations
Can't find checkstyle config	Ensure you're running from the `fe/` directory
IntelliJ formatting differs	Import `build-support/IntelliJ-code-format.xml` via Settings → Editor → Code Style