[FIXED] Why can I use Maven plugins without declaring them in pom.xml?

Issue

I have a pom.xml without declaring the versions-maven-plugin

<!-- no need to declare this in my pom.xml, plugin still works -->
<plugin>
    <!-- https://www.mojohaus.org/versions-maven-plugin/ -->
    <groupId>org.codehaus.mojo</groupId>
    <artifactId>versions-maven-plugin</artifactId>
    <version>2.7</version>
    <inherited>false</inherited>
</plugin>

When using mvn versions:display-property-updates, the plugin works even if I did not include the plugin in my pom.xml. Are all plugins from code org.codehaus.mojo already included in the maven distribution?

Solution

If you look at the default settings.xml file that ships with Maven, you will see:

pluginGroups

This is a list of additional group identifiers that will be searched when resolving plugins by their prefix, i.e. when invoking a command line like "mvn prefix:goal". Maven will automatically add the group identifiers "org.apache.maven.plugins" and "org.codehaus.mojo" if these are not already contained in the list.

You can see the effective settings with:

$ mvn help:effective-settings

If you want to add additional groups, you can do so in your local settings.xml (by default located at $HOME/.m2/settings.xml):

<?xml version="1.0" encoding="UTF-8"?>
<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0 http://maven.apache.org/xsd/settings-1.0.0.xsd">
  <pluginGroups>
    <!-- Add stackoverflow maven plugins -->
    <pluginGroup>com.stackoverflow.plugins</plugingroup>
  </pluginGroups>
</settings>

Answered By - Sean Bright