Maven Checkstyle "There are N errors reported" - Fix in CI

The maven-checkstyle-plugin ran with failOnViolation (or violationSeverity) such that style violations fail the build. At least one rule was breached, so checkstyle:check failed the build by design - this is the gate working, not an infrastructure problem.

What this error means

The build fails (often in verify) with Failed during checkstyle execution: There are N errors reported by Checkstyle, and the report lists each file, line, and rule violated.

mvn output

[ERROR] Failed to execute goal
org.apache.maven.plugins:maven-checkstyle-plugin:3.3.1:check (validate) on
project app: Failed during checkstyle execution: There are 3 errors reported
by Checkstyle 10.x with checkstyle.xml ruleset.

Common causes

New code breaks a configured style rule

Unused imports, line length, missing Javadoc, or naming-convention rules in the ruleset were violated. The check is configured to fail on them.

A stricter ruleset or version was introduced

Bumping the plugin/ruleset (e.g. a new Google/Sun style version) can surface violations that the previous version tolerated.

How to fix it

Read the report and fix the violations

The plugin writes a full report; reproduce locally and address each rule.

Terminal

mvn -B checkstyle:check
# detailed report:
#   target/checkstyle-result.xml  /  target/site/checkstyle.html

Tune severity or suppress a rule deliberately

If a rule is genuinely too strict, adjust violationSeverity or add a scoped suppression - not a blanket disable.

pom.xml (checkstyle)

<configuration>
  <configLocation>checkstyle.xml</configLocation>
  <violationSeverity>error</violationSeverity>
  <failOnViolation>true</failOnViolation>
</configuration>

How to prevent it

Run checkstyle locally / in pre-commit so violations are caught before CI.
Pin the checkstyle plugin and ruleset version so the rules do not drift unexpectedly.
Keep suppressions narrow and reviewed, not blanket disables.