Maven pluginManagement configuration inheritance strange behavior

Question

I'm using pluginManagement element in my parent pom.xml to configure plugins for all its children. For example, I have the following configuration:

<pluginManagement>
    <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-resources-plugin</artifactId>
        <version>2.4.3</version>
        <executions>
            <execution>
                <id>copy-artifacts</id>
                <phase>install</phase>
                <goals>
                    <goal>copy-resources</goal>
                </goals>
                <configuration>
                    <outputDirectory>some/where/else</outputDirectory>
                    <resources>
                        <resource>
                            <directory>some/another/resource</directory>
                        </resource>
                    </resources>
                </configuration>
            </execution>
        </executions>
    </plugin>

    <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-dependency-plugin</artifactId>
        <version>2.4</version>
        <executions>
            <execution>
                <id>copy-dependencies</id>
                <phase>install</phase>
                <goals>
                    <goal>copy-dependencies</goal>
                </goals>
                <configuration>
                    <outputDirectory>deps/dir</outputDirectory>
                </configuration>
            </execution>
        </executions>
    </plugin>
</pluginManagement>

The official documentation states that a plugin configured in pluginManagement still has to be added to plugins element in children poms. Indeed, if I remove this from child pom:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-dependency-plugin</artifactId>
</plugin>

then maven-dependency-plugin stops firing at install phase. However, it seems that it does not affect some other plugins, namely, maven-resource-plugin. Even if I do not have

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-resources-plugin</artifactId>
</plugin>

in my child pom, its copy-resources goal still fires at install phase and performs the work it is configured to do.

Why is this behavior present? Is there a list of plugins which are inherited always, or maybe I'm missing something?

Answer 1

The whole POM isn't visible; but given the behavior you're describing this is a jar, war, or ear, correct? The resource plugin is defined for those packaging types by default. It includes an execution that copies resources (as described by @maba).

Since the plugin definition is included in your child POM (even though YOU didn't put it there directly), Maven merges the execution defined in the <pluginManagement> section with the execution provided by Maven.

There is documentation describing the default lifecycle bindings by packaging type. Note the dependency plugin isn't mentioned; but resources is; that's why you observe the difference. Running with -X will show the plugin executions.

Answer 2

Maven always copies resources that are inside src/main/resources by default.

From Maven Getting Started Guide:

The simple rule employed by Maven is this: any directories or files placed within the ${basedir}/src/main/resources directory are packaged in your JAR with the exact same structure starting at the base of the JAR.