Find dependencies of a Maven Dependency object

Question

I'm writing a Maven 3 plugin that needs to know the transitive dependencies of a given org.apache.maven.model.Dependency. How can I do that?

Answer 1

So the following code should give you an impression how to do it.

@Mojo( name = "test", requiresDependencyResolution = ResolutionScope.COMPILE, defaultPhase = LifecyclePhase.PACKAGE ...)
public class TestMojo
    extends AbstractMojo
{
    @Parameter( defaultValue = "${project}", readonly = true )
    private MavenProject project;

    public void execute()
        throws MojoExecutionException, MojoFailureException
    {
        List<Dependency> dependencies = project.getDependencies();
        for ( Dependency dependency : dependencies )
        {
            getLog().info( "Dependency: " + getId(dependency) );
        }

        Set<Artifact> artifacts = project.getArtifacts();
        for ( Artifact artifact : artifacts )
        {
            getLog().info( "Artifact: " + artifact.getId() );
        }
    }

    private String getId(Dependency dep) {
        StringBuilder sb = new StringBuilder();
        sb.append( dep.getGroupId() );
        sb.append( ':' );
        sb.append( dep.getArtifactId() );
        sb.append( ':' );
        sb.append( dep.getVersion() );
        return sb.toString();
    }

}

The above code will give you the resolved artifacts as well as dependencies. You need to make a difference between the dependencies (in this case the project dependencies without transitive and the artifacts which are the solved artifacts incl. transitive.).

Most important is requiresDependencyResolution = ResolutionScope.COMPILE otherwise you will get null for getArtifacts().

The suggestion by Tunaki will work for any kind of artifact which is not part of your project...The question is what you really need?

Answer 2

In Maven 3, you access all dependencies in a tree-based form by relying on the maven-dependency-tree shared component:

A tree-based API for resolution of Maven project dependencies.

This component introduces the DependencyGraphBuilder that can build the dependency tree for a given Maven project. You can also filter artifacts with a ArtifactFilter, that has a couple of built-in implementations to filter by groupId, artifactId (IncludesArtifactFilter and ExcludesArtifactFilter), scope (ScopeArtifactFilter), etc. If the fiter is null, all dependencies are kept.

In your case, since you target a specific artifact, you could add a IncludesArtifactFilter with the pattern groupId:artifactId of your artifact. A sample code would be:

@Mojo(name = "foo")
public class MyMojo extends AbstractMojo {

    @Parameter(defaultValue = "${project}", readonly = true, required = true)
    private MavenProject project;

    @Parameter(defaultValue = "${session}", readonly = true, required = true)
    private MavenSession session;

    @Component(hint = "default")
    private DependencyGraphBuilder dependencyGraphBuilder;

    public void execute() throws MojoExecutionException, MojoFailureException {
        ArtifactFilter artifactFilter = new IncludesArtifactFilter(Arrays.asList("groupId:artifactId"));
        ProjectBuildingRequest buildingRequest = new DefaultProjectBuildingRequest(session.getProjectBuildingRequest());
        buildingRequest.setProject(project);
        try {
            DependencyNode rootNode = dependencyGraphBuilder.buildDependencyGraph(buildingRequest, artifactFilter);
            CollectingDependencyNodeVisitor visitor = new CollectingDependencyNodeVisitor();
            rootNode.accept(visitor);
            for (DependencyNode node : visitor.getNodes()) {
                System.out.println(node.toNodeString());
            }
        } catch (DependencyGraphBuilderException e) {
            throw new MojoExecutionException("Couldn't build dependency graph", e);
        }
    }

}

This gives access to the root node of the dependency tree, which is the current project. From that node, you can access all chidren by calling the getChildren() method. So if you want to list all dependencies, you can traverse that graph recursively. This component does provide a facility for doing that with the CollectingDependencyNodeVisitor. It will collect all dependencies into a List to easily loop through it.

For the Maven plugin, the following dependency is therefore necessary:

<dependency>
    <groupId>org.apache.maven.shared</groupId>
    <artifactId>maven-dependency-tree</artifactId>
    <version>3.0</version>
</dependency>