19. Maven Plugins

Maven Plugins

Maven Plugins

All Maven goals, even the default behaviors, are performed by plugins. Here are the default bindings for JAR projects. You can see that each phase has a groupId, artifactId, and version preceding an additional string, which is the name of the goal that plugin will execute. For examples, in the <compile> phase, we execute the goal compile of the plugin maven-compiler-plugin. That plugin is in the group org.apache.maven.plugins and the default version is 3.1.

<phases>
  <process-resources> org.apache.maven.plugins:maven-resources-plugin:2.6:resources </process-resources>
  <compile> org.apache.maven.plugins:maven-compiler-plugin:3.1:compile </compile>
  <process-test-resources> org.apache.maven.plugins:maven-resources-plugin:2.6:testResources </process-test-resources>
  <test-compile> org.apache.maven.plugins:maven-compiler-plugin:3.1:testCompile </test-compile>
  <test> org.apache.maven.plugins:maven-surefire-plugin:2.12.4:test </test>
  <package> org.apache.maven.plugins:maven-jar-plugin:2.4:jar </package>
  <install> org.apache.maven.plugins:maven-install-plugin:2.4:install </install>
  <deploy> org.apache.maven.plugins:maven-deploy-plugin:2.7:deploy </deploy>
</phases>

You can find a list of a wide variety of plugins used by Maven on the documentation site:
https://maven.apache.org/plugins/index.html

Plugin Management vs. Plugins.

You can customize the versions of these plugins in the <pluginManagement> element of the build. Changes in that area will affect all children projects as well. If you wish to customize a plugin for this project only, place those changes in the <plugins> element instead.

<build>
  <plugins>
    <plugin>
      ... customization for this project only
    </plugin>
  </plugins>
  <pluginManagement>
    <plugins>
      <plugin>
        ... customization for all projects that inherit this as well
      </plugin>
    </plugins>
  </pluginManagement>

Customizing Plugin Execution

Binding Goal to Phase

To bind a plugin goal to a phase, we add an <execution> element to the plugin definition. This example binds the do-blockchain goal of the plugin called my-blockchain-plugin to the test phase. Now whenever Maven executes that phase, my goal will be run.

<plugin>
  <groupId>com.udacity.jpnd</groupId>

  <artifactId>my-blockchain-plugin</artifactId>
  <executions>
    <execution>
      <phase>test</phase>
      <goals>
        <goal>do-blockchain</goal>
      </goals>
    </execution>
  </executions>
</plugin>

Configuring Plugins

You can pass additional properties to plugins using the <configuration> element. We can modify the above to pass in the <bitcoins> property to our plugin with the following example:

<plugin>
  <groupId>com.udacity.jpnd</groupId>
  <artifactId>my-blockchain-plugin</artifactId>
  <executions>
    <execution>
      <phase>test</phase>
      <goals>
        <goal>do-blockchain</goal>
      </goals>
      <configuration>
        <bitcoins>all</bitcoins>
      </configuration>
    </execution>
  </executions>
</plugin>