Mastering Maven Artifact Downloads with Eclipse Aether: A Developer's Guide

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This technical guide demonstrates how to programmatically download Maven artifacts using Eclipse Aether in Maven 3.1 and later versions. The article presents a complete Maven plugin implementation that showcases the process of resolving and downloading artifacts from remote repositories. The code example includes comprehensive configuration of the repository system, dependency collection, and artifact resolution, making it an essential reference for developers working with Maven's dependency management system or creating custom Maven plugins that require runtime artifact downloads.

2 Minutes reading time

Maven

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Starting with Maven 3.1, Sonatype Aether(github.com/sonatype/sonatype-aether ) was replaced with Eclipse Eather(www.eclipse.org/aether ). Now, sometimes we need do download additional Artifacts from Maven repositories during execution time of custom Maven plugins. As the Maven and Aether documentation is not very handsome, here is a short example about how to programmatically download and resolve Maven Artifacts using Maven 3.1 and later with the Eclipse Aether API:

import java.io.File;
import java.util.ArrayList;
import java.util.List;

import org.apache.maven.execution.MavenSession;
import org.apache.maven.plugin.AbstractMojo;
import org.apache.maven.plugin.BuildPluginManager;
import org.apache.maven.plugin.MojoExecutionException;
import org.apache.maven.plugins.annotations.Component;
import org.apache.maven.plugins.annotations.LifecyclePhase;
import org.apache.maven.plugins.annotations.Mojo;
import org.apache.maven.plugins.annotations.Parameter;
import org.apache.maven.project.MavenProject;

import org.eclipse.aether.RepositorySystem;
import org.eclipse.aether.RepositorySystemSession;
import org.eclipse.aether.artifact.Artifact;
import org.eclipse.aether.artifact.DefaultArtifact;
import org.eclipse.aether.collection.CollectRequest;
import org.eclipse.aether.graph.DependencyFilter;
import org.eclipse.aether.repository.RemoteRepository;
import org.eclipse.aether.resolution.ArtifactResult;
import org.eclipse.aether.resolution.DependencyRequest;
import org.eclipse.aether.resolution.DependencyResolutionException;
import org.eclipse.aether.resolution.DependencyResult;
import org.eclipse.aether.util.artifact.JavaScopes;
import org.eclipse.aether.util.filter.DependencyFilterUtils;

@Mojo(name = "download-mojo", defaultPhase = LifecyclePhase.PACKAGE)
public class DownloadMojo extends AbstractMojo {

    @Component
    private MavenProject mavenProject;

    @Component
    private MavenSession mavenSession;

    @Component
    private BuildPluginManager pluginManager;

    @Component
    private RepositorySystem repositorySystem;

    @Parameter(defaultValue = "${repositorySystemSession}", readonly = true)
    private RepositorySystemSession repositorySystemSession;

    @Parameter(defaultValue = "${project.remotePluginRepositories}", readonly = true)
    private List<RemoteRepository> remoteRepositories;

    public void execute() throws MojoExecutionException {
              // We want to collect the files in our local repository here
              List theResult = new ArrayList<>();

              String theGroupId = ""; // Replace with your Artifact
              String theArtifactId = ""; // Replace with your Artifact
              String theArtifactVersion = ""; // Replace with your Artifact
              String theClassifier = ""; // Replace with your Artifact
              String theExtension = ""; // Replace with your Artifact
              String theScope = JavaScopes.COMPILE; // Replace with your Artifact

              // We create a collect request here
              // By adding the remote repositories we force Aether to download artifacts if they
              // are not already in the local reposaitory
              CollectRequest theCollectRequest = new CollectRequest();
              theCollectRequest.setRoot(new org.eclipse.aether.graph.Dependency(new DefaultArtifact(theGroupId, theArtifactId,
                               theClassifier, theExtension, theArtifactVersion), theScope));
              for (RemoteRepository theRepository : remoteRepositories) {
                        theCollectRequest.addRepository(theRepository);
              }

              // We filter dependencies here, as we only want compile scope
              DependencyFilter theDependencyFilter = DependencyFilterUtils.classpathFilter(theScope);
              DependencyRequest theDependencyRequest = new DependencyRequest(theCollectRequest, theDependencyFilter);
              try {
                        DependencyResult theDependencyResult = repositorySystem.resolveDependencies(repositorySystemSession, theDependencyRequest);
                        for (ArtifactResult theArtifactResult : theDependencyResult.getArtifactResults()) {
                                  Artifact theResolved = theArtifactResult.getArtifact();
                                  // Now we have the artifact file locally stored available
                                  // and we can do something with it
                                  File theLocallyStoredFile = theResolved.getFile();
                                  theResult.add(theLocallyStoredFile);
                        }
               } catch (DependencyResolutionException e) {
                        throw new MojoExecutionException("Error while resolving dependency", e);
               }
    }
}

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Git revision: 2e692ad