import org.apache.maven.shared.dependency.tree.traversal.DependencyNodeVisitor; //导入依赖的package包/类
@Override
public void execute() throws MojoExecutionException, MojoFailureException {
    try {
        // find the nar dependency
        Artifact narArtifact = null;
        for (final Artifact artifact : project.getDependencyArtifacts()) {
            if (NAR.equals(artifact.getType())) {
                // ensure the project doesn't have two nar dependencies
                if (narArtifact != null) {
                    throw new MojoExecutionException("Project can only have one NAR dependency.");
                }

                // record the nar dependency
                narArtifact = artifact;
            }
        }

        // ensure there is a nar dependency
        if (narArtifact == null) {
            throw new MojoExecutionException("Project does not have any NAR dependencies.");
        }

        // build the project for the nar artifact
        final ProjectBuildingRequest narRequest = new DefaultProjectBuildingRequest();
        narRequest.setRepositorySession(repoSession);
        narRequest.setSystemProperties(System.getProperties());
        final ProjectBuildingResult narResult = projectBuilder.build(narArtifact, narRequest);

        // get the artifact handler for excluding dependencies
        final ArtifactHandler narHandler = excludesDependencies(narArtifact);
        narArtifact.setArtifactHandler(narHandler);

        // nar artifacts by nature includes dependencies, however this prevents the
        // transitive dependencies from printing using tools like dependency:tree.
        // here we are overriding the artifact handler for all nars so the
        // dependencies can be listed. this is important because nar dependencies
        // will be used as the parent classloader for this nar and seeing what
        // dependencies are provided is critical.
        final Map<String, ArtifactHandler> narHandlerMap = new HashMap<>();
        narHandlerMap.put(NAR, narHandler);
        artifactHandlerManager.addHandlers(narHandlerMap);

        // get the dependency tree
        final DependencyNode root = dependencyTreeBuilder.buildDependencyTree(narResult.getProject(), localRepository, null);

        // write the appropriate output
        DependencyNodeVisitor visitor = null;
        if ("tree".equals(mode)) {
            visitor = new TreeWriter();
        } else if ("pom".equals(mode)) {
            visitor = new PomWriter();
        }

        // ensure the mode was specified correctly
        if (visitor == null) {
            throw new MojoExecutionException("The specified mode is invalid. Supported options are 'tree' and 'pom'.");
        }

        // visit and print the results
        root.accept(visitor);
        getLog().info("--- Provided NAR Dependencies ---\n\n" + visitor.toString());
    } catch (DependencyTreeBuilderException | ProjectBuildingException e) {
        throw new MojoExecutionException("Cannot build project dependency tree", e);
    }
}