Is effective-pom a merge between super pom and application POM

Question

I have tried to generate effective pom on sample application using mvn help:effective-pom command. http://books.sonatype.com/mvnref-book/reference/pom-relationships-sect-pom.html at this article it says effective pom is a merge between super pom and application pom.

But, When I look at my effective-pom, it contains elements which are not included in the either super pom or effective pom.

Is there other factor deciding what goes into effective pom.

Given below is the super pom and application pom, Both of these pom's does not have mavne-jar-plugin or maven-compiler-plugin, but in my effective-pom , I can see those plugins in the build section. So how does it get added.

Thanks in advance for any help on clarifying this issue

Super POM

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<!-- START SNIPPET: superpom -->
<project>
  <modelVersion>4.0.0</modelVersion>

  <repositories>
    <repository>
      <id>central</id>
      <name>Central Repository</name>
      <url>http://repo.maven.apache.org/maven2</url>
      <layout>default</layout>
      <snapshots>
        <enabled>false</enabled>
      </snapshots>
    </repository>
  </repositories>

  <pluginRepositories>
    <pluginRepository>
      <id>central</id>
      <name>Central Repository</name>
      <url>http://repo.maven.apache.org/maven2</url>
      <layout>default</layout>
      <snapshots>
        <enabled>false</enabled>
      </snapshots>
      <releases>
        <updatePolicy>never</updatePolicy>
      </releases>
    </pluginRepository>
  </pluginRepositories>

  <build>
    <directory>${project.basedir}/target</directory>
    <outputDirectory>${project.build.directory}/classes</outputDirectory>
    <finalName>${project.artifactId}-${project.version}</finalName>
    <testOutputDirectory>${project.build.directory}/test-classes</testOutputDirectory>
    <sourceDirectory>${project.basedir}/src/main/java</sourceDirectory>
    <scriptSourceDirectory>src/main/scripts</scriptSourceDirectory>
    <testSourceDirectory>${project.basedir}/src/test/java</testSourceDirectory>
    <resources>
      <resource>
        <directory>${project.basedir}/src/main/resources</directory>
      </resource>
    </resources>
    <testResources>
      <testResource>
        <directory>${project.basedir}/src/test/resources</directory>
      </testResource>
    </testResources>
    <pluginManagement>
      <!-- NOTE: These plugins will be removed from future versions of the super POM -->
      <!-- They are kept for the moment as they are very unlikely to conflict with lifecycle mappings (MNG-4453) -->
      <plugins>
        <plugin>
          <artifactId>maven-antrun-plugin</artifactId>
          <version>1.3</version>
        </plugin>
        <plugin>
          <artifactId>maven-assembly-plugin</artifactId>
          <version>2.2-beta-5</version>
        </plugin>
        <plugin>
          <artifactId>maven-dependency-plugin</artifactId>
          <version>2.1</version>
        </plugin>
        <plugin>
          <artifactId>maven-release-plugin</artifactId>
          <version>2.0</version>
        </plugin>
      </plugins>
    </pluginManagement>
  </build>

  <reporting>
    <outputDirectory>${project.build.directory}/site</outputDirectory>
  </reporting>

  <profiles>
    <!-- NOTE: The release profile will be removed from future versions of the super POM -->
    <profile>
      <id>release-profile</id>

      <activation>
        <property>
          <name>performRelease</name>
          <value>true</value>
        </property>
      </activation>

      <build>
        <plugins>
          <plugin>
            <inherited>true</inherited>
            <artifactId>maven-source-plugin</artifactId>
            <executions>
              <execution>
                <id>attach-sources</id>
                <goals>
                  <goal>jar</goal>
                </goals>
              </execution>
            </executions>
          </plugin>
          <plugin>
            <inherited>true</inherited>
            <artifactId>maven-javadoc-plugin</artifactId>
            <executions>
              <execution>
                <id>attach-javadocs</id>
                <goals>
                  <goal>jar</goal>
                </goals>
              </execution>
            </executions>
          </plugin>
          <plugin>
            <inherited>true</inherited>
            <artifactId>maven-deploy-plugin</artifactId>
            <configuration>
              <updateReleaseInfo>true</updateReleaseInfo>
            </configuration>
          </plugin>
        </plugins>
      </build>
    </profile>
  </profiles>

</project>
<!-- END SNIPPET: superpom -->

Application POM

<project>
    <modelVersion>4.0.0</modelVersion>
    <groupId>org.sonatype.mavenbook.ch08</groupId>
    <artifactId>simplest-project</artifactId>
    <packaging>jar</packaging>
    <version>1</version>
</project>

effective pom

Answer 1

Effective POM is composed of Super POM + Application POM(s) + settings.xml contents + plugins bound to the lifecycle by default based on the packaging type chosen (thus, based on one element in the Application POM).

You asked about maven-jar-plugin and maven-compiler-plugin. These are bound to the lifecycle by default because your application POM specifies jar packaging.

You can see the default bindings in $YOUR_REPO_LOCATION\org\apache\maven\maven-core\3.0.x\maven-core-3.0.x.jar\META-INF\plexus\components.xml or in the documentation.

Answer 2

If I remember correctly, effective POM means the actual POM to be used.

Incorporating settings in super POM is part of it. It also includes a lot other things, like applying parent POM, applying profiles, substituting properties, and etc.

I think it will be better if you can give some snippet of the settings you thought that comes from no where, so that we can identify where do they come from.