how does maven handle duplicate plugin declaration

Question

A large undocumented project whose build I am trying to cleanup has maven warnings about duplicate plugin declaration.

The pom.xml is something like

<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-war-plugin</artifactId>
  <configuration>
    <webResources>
      <resource>
        <directory>${project.basedir}/src/main/webapp</directory>
      </resource>
    </webResources>
  </configuration>
</plugin>

<plugin>
  <artifactId>maven-war-plugin</artifactId>
  <configuration>
    <attachClasses>true</attachClasses>
    <classesClassifier>classes</classesClassifier>
  </configuration>
</plugin>

I need to change it so it does not log warnings yet behaves exactly as it does now.

I guess, there are three possibilities:

• first declaration wins
• last declaration wins
• all encountered declarations are merged XML-wise

But which one is it?

Answer 1

Run with debug logging (-X), find the occurrences/mentions of the war plugin in the log, and see what configuration is present. Then make your POMs look like that configuration.