Programmatically resolving Maven dependencies outside of a plugin - get RepositorySystemSession and RepositorySystem

Question

Maybe this is going to be a larger task than I had originally thought, but regardless, I'm trying to load a MavenProject from a file and then resolve its dependencies. I've got the code for both bits but I'm missing some object references that I need; specifically I need to get instances of RepositorySystemSession and RepositorySystem. Any tips?

Note: I have tagged this question with maven-plugin, but this is not a Maven plugin. I am happy to mandate Maven 3 (think I already have anyway..)

Here's the code I have so far:

Constructing the MavenProject:

public static MavenProject loadProject(File pomFile) throws Exception
{
    MavenProject ret = null;
    MavenXpp3Reader mavenReader = new MavenXpp3Reader();

    if (pomFile != null && pomFile.exists())
    {
        FileReader reader = null;

        try
            {
            reader = new FileReader(pomFile);
            Model model = mavenReader.read(reader);
            model.setPomFile(pomFile);

            ret = new MavenProject(model);
        }
        finally
        {
            // Close reader
        }
    }

    return ret;
}

Resolving dependencies:

public static List<Dependency> getArtifactsDependencies(MavenProject project, String dependencyType, String scope) throws Exception
{    
    DefaultArtifact pomArtifact = new DefaultArtifact(project.getId());

    RepositorySystemSession repoSession = null; // TODO
    RepositorySystem repoSystem = null; // TODO

    List<RemoteRepository> remoteRepos = project.getRemoteProjectRepositories();
    List<Dependency> ret = new ArrayList<Dependency>();

    Dependency dependency = new Dependency(pomArtifact, scope);

    CollectRequest collectRequest = new CollectRequest();
    collectRequest.setRoot(dependency);
    collectRequest.setRepositories(remoteRepos);

    DependencyNode node = repoSystem.collectDependencies(repoSession, collectRequest).getRoot();
    DependencyRequest projectDependencyRequest = new DependencyRequest(node, null);

    repoSystem.resolveDependencies(repoSession, projectDependencyRequest);

    PreorderNodeListGenerator nlg = new PreorderNodeListGenerator();
    node.accept(nlg);

    ret.addAll(nlg.getDependencies(true));

    return ret;
}

I realise this might be an unusual request, maybe I should just scrap what I was trying to do and wrap it as a plugin...but I kind of just want to finish what I started now! Thanks in advance.

Answer 1

Try jcabi-aether, which is a wrapper around Apache Aether from Sonatype:

final File repo = this.session.getLocalRepository().getBasedir();
final Collection<Artifact> deps = new Aether(this.getProject(), repo).resolve(
  new DefaultArtifact("junit", "junit-dep", "", "jar", "4.10"),
  JavaScopes.RUNTIME
);

If you are outside of Maven plugin:

final File repo = new File(System.getProperty("java.io.tmpdir"), "my-repo");
final MavenProject project = new MavenProject();
project.setRemoteArtifactRepositories(
  Arrays.asList(
    new RemoteRepository(
      "maven-central",
      "default",
      "http://repo1.maven.org/maven2/"
    )
  )
);
final Collection<Artifact> deps = new Aether(project, repo).resolve(
  new DefaultArtifact("junit", "junit-dep", "", "jar", "4.10"),
  JavaScopes.RUNTIME
);