D-Net

    public static Qualifier getQualifier(final String classValue, final String schemeValue) {

        return Qualifier.newBuilder()

                .setSchemeid(schemeValue)

                .setSchemename(schemeValue)

                .setClassname(classValue)

                .setClassid(classValue)

                .build();

    }

    private static StructuredProperty getPid(final JsonObject localIdentifier, final Map<String, ScholExplorerConfiguration> conf) {

        final String pidType = getStringValue(localIdentifier, "type");

        final ScholExplorerConfiguration configuration = conf.get(pidType);

        if (configuration.getCleandPidType() == null) {

            return null;

        }

        final String pid = getStringValue(localIdentifier, "id");

        return StructuredProperty.newBuilder()

                .setValue(pid)

                .setQualifier(getQualifier(configuration.getCleandPidType(), "dnet:pid_types"))

                .build();

    }

    public static String getStringValue(final JsonObject root, final String key) {

        if (root.has(key) && !root.get(key).isJsonNull())

            return root.get(key).getAsString();

        return null;

    }

    public static List<String> getArrayValues(final JsonObject root, final String key) {

        if (root.has(key) && root.get(key).isJsonArray()) {

            final JsonArray asJsonArray = root.get(key).getAsJsonArray();

            final List<String> result = new ArrayList<>();

            asJsonArray.forEach(it -> {

                if (StringUtils.isNotBlank(it.getAsString())) {

                    result.add(it.getAsString());

                }

            });

            return result;

        }

        return new ArrayList<>();

    }