* @return the extension or an empty string if none, never {@code null}
     */
    @Nonnull
    String getExtension();

    /**
     * Unique id identifying this artifact
     */
    @Nonnull
    default String getId() {
        return getGroupId()
                + ":" + getArtifactId()
                + ":" + getExtension()
                + (getClassifier().isEmpty() ? "" : ":" + getClassifier())

/**
 * The type of signature.
 */
public interface SignatureType {

    /**
     * The file extension (without the leading dot) associated to this type of signature.
     */
    @Input
    String getExtension();

    /**
     * Calculates the file where to store the signature of the given file to be signed.
     *
     * @param toSign The file to be signed

     * @return the unique identifier
     */
    @Nonnull
    default String key() {
        return getGroupId()
                + ':'
                + getArtifactId()
                + ':'
                + getExtension()
                + (getClassifier().isEmpty() ? "" : ":" + getClassifier())
                + ':'
                + getVersion();
    }

    /**
     * The groupId of the artifact.
     *

            verified.add(artifact);
        }
    }

    private void checkNotDuplicate(MavenNormalizedPublication publication, Set<MavenArtifact> artifacts, String extension, String classifier) {
        for (MavenArtifact artifact : artifacts) {

    }

    @Override
    public String getType() {
        return artifactName.getType();
    }

    @Nullable
    @Override
    public String getExtension() {
        return artifactName.getExtension();
    }

    @Nullable
    @Override
    public String getClassifier() {
        return artifactName.getClassifier();
    }

        if (ivyArtifactName == null) {
            ArtifactFile names = new ArtifactFile(relativeUrl, uniqueVersion());
            ivyArtifactName = new DefaultIvyArtifactName(names.getName(), names.getExtension(), names.getExtension(), names.getClassifier());
        }
        return ivyArtifactName;
    }

    @Override
    public TaskDependency getBuildDependencies() {
        return TaskDependencyInternal.EMPTY;
    }

            && matches(moduleId.getName(), module.getName())
            && matches(ivyArtifactName.getName(), artifact.getName())
            && matches(ivyArtifactName.getExtension(), artifact.getExtension())
            && matches(ivyArtifactName.getType(), artifact.getType());
    }

    @Override
    public boolean mayExcludeArtifacts() {
        return isArtifactExclude;
    }

            return classifier;
        } else {
            return artifact.getClassifier();
        }
    }

    @Override
    public String getExtension() {
        if (extension != null) {
            return extension;
        } else {
            return artifact.getExtension();
        }
    }

    @Override
    public String getVersion() {
        if (version != null) {
            return version;

    @Nonnull
    Session getSession();

    String getGroupId();

    String getArtifactId();

    String getVersion();

    String getClassifier();

    String getExtension();

    String getType();

    static ArtifactFactoryRequest build(
            Session session, String groupId, String artifactId, String version, String extension) {
        return ArtifactFactoryRequest.builder()

    }

    /**
     * @throws Exception
     */
    public void testGetExtension() throws Exception {
        assertEquals("1", "xml", ResourceUtil.getExtension("aaa/bbb.xml"));
        assertEquals("2", null, ResourceUtil.getExtension("aaa"));
    }

    /**
     * @throws Exception
     */
    public void testRemoteExtension() throws Exception {