How can I get a maven build to fail on duplicate dependencies?

Question

If I have two dependencies which are the same in the same pom, I want the build to fail. Currently I can detect it happening with the Maven Dependency Plugin's "analyze-duplicate". However, there's no option to failOnWarning like some of the others (plus, it prints at Info level, not Warning). Is there an alternative to extending this?

Answer 1

Generally, when you want the build to fail for some reason, the good plugin to look into the Maven Enforcer Plugin. This plugin can be configured with a set of rules that, when verified, will fail the build.

In this case, it would need to be a rule that checks for duplicate dependencies, and there is a built-in rule just for that: <banDuplicatePomDependencyVersions>. As such, you could have

<plugin>
  <artifactId>maven-enforcer-plugin</artifactId>
  <version>1.4.1</version>
  <executions>
    <execution>
      <id>enforce-no-duplicate-dependencies</id>
      <goals>
        <goal>enforce</goal>
      </goals>
      <configuration>
        <rules>
          <banDuplicatePomDependencyVersions/>
        </rules>
      </configuration>
    </execution>
  </executions>
</plugin>

This rule is unfortunately not documented (yet, it will be in the next version, see MENFORCER-259), but it exists since version 1.3 of the plugin (MENFORCER-152).

What this rule does is checking that there are no 2 duplicate declaration with the same 'dependencies.dependency.(groupId:artifactId:type:classifier)'; which is to say that two declared dependencies with the same group id and artifact id declared in the POM will have to have a different type and/or classifier.