Using Resolver in Maven Plugins

Apache Maven 3.x uses Resolver (former Aether) for repository tasks and Maven plugins that target Maven 3.x can do so as well. To start, you likely want to add the following dependencies to your plugin POM:

<project>
  ...
  <prerequisites>
    <!-- Maven 3.1.0 is the earliest version using Eclipse Aether, Maven 3.0.x uses the incompatible predecessor Sonatype Aether -->
    <maven>3.1</maven>
  </prerequisites>

  <dependencies>
    <dependency>
      <!-- required in all cases -->
      <groupId>org.apache.maven.resolver</groupId>
      <artifactId>maven-resolver-api</artifactId>
      <version>1.9.22</version>
      <scope>provided</scope>
    </dependency>
    <dependency>
      <!-- optional helpers, might be superfluous depending on your use case -->
      <groupId>org.apache.maven.resolver</groupId>
      <artifactId>maven-resolver-util</artifactId>
      <version>1.9.22</version>
      <!-- Scope: use compile to make plugin work in Maven 3.8 and earlier -->
      <scope>compile</scope>
    </dependency>
    ...
  </dependencies>
  ...
</project>

Note: At runtime, the actual version of maven-resolver-api being used is enforced by the Maven core, just like other Maven APIs. So be sure to compile/test your plugin against the version of maven-resolver-api that is used by the minimum version of Maven that your plugin wants to support.

Next, in your mojo source, you need to grab the repository related components and parameters:

import org.eclipse.aether.RepositorySystem;
import org.eclipse.aether.RepositorySystemSession;
import org.eclipse.aether.repository.RemoteRepository;
...

public class MyMojo extends AbstractMojo
{

    /**
     * The entry point to resolver (a.k.a. Aether), i.e. the component doing all the work.
     */
    @Component
    private RepositorySystem repoSystem;

    /**
     * The current repository/network configuration of Maven.
     */
    @Parameter(defaultValue="${repositorySystemSession}", readonly = true)
    private RepositorySystemSession repoSession;

    /**
     * The project's remote repositories to use for the resolution of project dependencies.
     */
    @Parameter(defaultValue = "${project.remoteProjectRepositories}", readonly = true)
    private List<RemoteRepository> projectRepos;

    /**
     * The project's remote repositories to use for the resolution of plugins and their dependencies.
     */
    @Parameter(defaultValue = "${project.remotePluginRepositories}", readonly = true)
    private List<RemoteRepository> pluginRepos;

    // Your other mojo parameters and code here
    ...
}

Usually, you need only projectRepos or pluginRepos depending on the nature of artifacts your plugin is dealing with, so the other plugin parameter would be superfluous in that case. But in general, the bits shown above should give you all handles that you need to work with Aether from within a Maven plugin.