How to get access to Maven’s dependency hierarchy within a plugin

The dependency plugin has the tree goal that does most of this work. It processes a MavenProject using the DependencyTreeBuilder, this returns a DependencyNode with hierarchical information about the resolved dependencies (and their transitive dependencies).

You can copy much of the code directly from the TreeMojo. It uses the CollectingDependencyNodeVisitor to traverse the tree and produce a List of all the nodes.

You can access the Artifact for the node by calling getArtifact(), then get the artifact information as needed. To get the exclusion reason, DependencyNode has a getState() method that returns an int indicating if the dependency has been included, or if not what the reason for omitting it was (there are constants in the DependencyNode class to check the return value against)

//All components need this annotation, omitted for brevity

/**
 * @component
 * @required
 * @readonly
 */
private ArtifactFactory artifactFactory;
private ArtifactMetadataSource artifactMetadataSource;
private ArtifactCollector artifactCollector;
private DependencyTreeBuilder treeBuilder;
private ArtifactRepository localRepository;
private MavenProject project;

public void execute() throws MojoExecutionException, MojoFailureException {
    try {
        ArtifactFilter artifactFilter = new ScopeArtifactFilter(null);

        DependencyNode rootNode = treeBuilder.buildDependencyTree(project,
                localRepository, artifactFactory, artifactMetadataSource,
                artifactFilter, artifactCollector);

        CollectingDependencyNodeVisitor visitor = 
            new CollectingDependencyNodeVisitor();

        rootNode.accept(visitor);

        List<DependencyNode> nodes = visitor.getNodes();
        for (DependencyNode dependencyNode : nodes) {
            int state = dependencyNode.getState();
            Artifact artifact = dependencyNode.getArtifact();
            if(state == DependencyNode.INCLUDED) {                    
                //...
            } 
        }
    } catch (DependencyTreeBuilderException e) {
        // TODO handle exception
        e.printStackTrace();
    }
}