Download artifact from Maven repository in Java program

Question

I need to write Java code that downloads a given artifact (GAV) from a given Maven repository. In the past I used the REST interface of Nexus 2 (which is quite easy) but I would like to have something which is independent of the repository (Nexus 2, Nexus 3, Artifactory) used.

In Fetching Maven artifacts programmatically a similar question is asked, but the main answer is from 2014 and suggests a library that was not updated since 2014.

Answer 1

One can do the following thing with Aether (Version 1.1.0):

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

import org.apache.maven.repository.internal.MavenRepositorySystemUtils;
import org.eclipse.aether.DefaultRepositorySystemSession;
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.connector.basic.BasicRepositoryConnectorFactory;
import org.eclipse.aether.impl.DefaultServiceLocator;
import org.eclipse.aether.repository.LocalRepository;
import org.eclipse.aether.repository.RemoteRepository;
import org.eclipse.aether.resolution.ArtifactRequest;
import org.eclipse.aether.resolution.ArtifactResolutionException;
import org.eclipse.aether.resolution.ArtifactResult;
import org.eclipse.aether.spi.connector.RepositoryConnectorFactory;
import org.eclipse.aether.spi.connector.transport.TransporterFactory;
import org.eclipse.aether.transport.file.FileTransporterFactory;
import org.eclipse.aether.transport.http.HttpTransporterFactory;


public class ArtifactDownload
{

  private static RepositorySystem newRepositorySystem()
  {
    DefaultServiceLocator locator = MavenRepositorySystemUtils
        .newServiceLocator();
    locator.addService(RepositoryConnectorFactory.class,
        BasicRepositoryConnectorFactory.class);
    locator.addService(TransporterFactory.class, FileTransporterFactory.class);
    locator.addService(TransporterFactory.class, HttpTransporterFactory.class);
    return locator.getService(RepositorySystem.class);

  }

  private static RepositorySystemSession newSession(RepositorySystem system,
      File localRepository)
  {
    DefaultRepositorySystemSession session = MavenRepositorySystemUtils
        .newSession();
    LocalRepository localRepo = new LocalRepository(localRepository.toString());
    session.setLocalRepositoryManager(system.newLocalRepositoryManager(session,
        localRepo));
    return session;
  }


  public static File getArtifactByAether(String groupId, String artifactId,
      String version, String classifier, String packaging, File localRepository)
      throws IOException
  {
    RepositorySystem repositorySystem = newRepositorySystem();
    RepositorySystemSession session = newSession(repositorySystem,
        localRepository);

    Artifact artifact = new DefaultArtifact(groupId, artifactId, classifier,
        packaging, version);
    ArtifactRequest artifactRequest = new ArtifactRequest();
    artifactRequest.setArtifact(artifact);

    List<RemoteRepository> repositories = new ArrayList<>();

    RemoteRepository remoteRepository = new RemoteRepository.Builder("public",
        "default", "http://somerepo").build();

    repositories.add(remoteRepository);

    artifactRequest.setRepositories(repositories);
    File result;

    try
    {
      ArtifactResult artifactResult = repositorySystem.resolveArtifact(session,
          artifactRequest);
      artifact = artifactResult.getArtifact();
      if (artifact != null)
      {
        result = artifact.getFile();
      }
      else
      {
        result = null;
      }
    }
    catch (ArtifactResolutionException e)
    {
      throw new IOException("Artefakt " + groupId + ":" + artifactId + ":"
          + version + " konnte nicht heruntergeladen werden.");
    }

    return result;

  }
}

using the following artifacts

    <dependency>
      <groupId>org.eclipse.aether</groupId>
      <artifactId>aether-api</artifactId>
      <version>${aetherVersion}</version>
    </dependency>
    <dependency>
      <groupId>org.eclipse.aether</groupId>
      <artifactId>aether-spi</artifactId>
      <version>${aetherVersion}</version>
    </dependency>
    <dependency>
      <groupId>org.eclipse.aether</groupId>
      <artifactId>aether-impl</artifactId>
      <version>${aetherVersion}</version>
    </dependency>
    <dependency>
      <groupId>org.eclipse.aether</groupId>
      <artifactId>aether-connector-basic</artifactId>
      <version>${aetherVersion}</version>
    </dependency>
    <dependency>
      <groupId>org.eclipse.aether</groupId>
      <artifactId>aether-transport-file</artifactId>
      <version>${aetherVersion}</version>
    </dependency>
    <dependency>
      <groupId>org.eclipse.aether</groupId>
      <artifactId>aether-transport-http</artifactId>
      <version>${aetherVersion}</version>
    </dependency>
    <dependency>
      <groupId>org.apache.maven</groupId>
      <artifactId>maven-aether-provider</artifactId>
      <version>${mavenVersion}</version>
    </dependency>

with

<aetherVersion>1.1.0</aetherVersion>
<mavenVersion>3.3.3</mavenVersion>

Answer 2

I recently found myself in the situation to have the requirement to download files from a maven repository. I stumbled over (at: https://www.hascode.com/2017/09/downloading-maven-artifacts-from-a-pom-file-programmatically-with-eclipse-aether/#comment-5602) following https://github.com/shrinkwrap/resolver library which is much easier to use than the Eclipse Aether project.

String artifactoryUrl = "https://your-repo:port/repository";
String[] requiredTypes = new String[] { "zip", "xml" };

for (String requiredType : requiredTypes) {
    MavenResolvedArtifact[] result = Maven.configureResolver()
            .withMavenCentralRepo(false)
            .withRemoteRepo("default", artifactoryUrl, "default")
            .useLegacyLocalRepo(true) // You can also set to ignore origin of artifacts present in local repository via useLegacyLocalRepo(true) method.
            .resolve(
                    group + ":" +
                    id + ":" +
                    requiredType + ":" +
                    version
            )
            .withTransitivity()
            .asResolvedArtifact();

    for (MavenResolvedArtifact mavenResolvedArtifact : result) {
        System.out.println(mavenResolvedArtifact);
        System.out.println(mavenResolvedArtifact.asFile().getAbsolutePath());
    }
 }

Answer 3

You are describing the features of maven-dependency-plugin (get goal)

So there is Java code that does exactly what you want, in the context of a maven plugin.

I would simply

• retrieve the source code of the get plugin from github
• remove all the maven plugin stuff (@Component dependency injection, parameters)
• integrate the gist of it where you need it (and add dependencies on the internal maven libraries that are required)