io.telicent.smart.cache.sources.kafka.serializers.GraphSerializer Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of event-source-kafka Show documentation
There is a newer version: 0.24.1
/**
 * Copyright (C) Telicent Ltd
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package io.telicent.smart.cache.sources.kafka.serializers;

import org.apache.commons.lang3.StringUtils;
import org.apache.jena.graph.Graph;
import org.apache.jena.riot.Lang;
import org.apache.jena.riot.RDFLanguages;
import org.apache.jena.riot.RDFWriterBuilder;
import org.apache.kafka.common.header.Headers;
import org.apache.kafka.common.serialization.Serializer;

import java.io.ByteArrayOutputStream;

/**
 * A Kafka serializer for RDF Graphs
 */
public class GraphSerializer extends AbstractRdfSerdes implements Serializer {
    /**
     * Creates a new serializer that uses NTriples as the output serialization
     */
    public GraphSerializer() {
        this(RDFLanguages.NTRIPLES);
    }

    /**
     * Creates a new serializer that uses the given RDF Language as the output serialization
     *
     * @param defaultLang Default language
     */
    public GraphSerializer(Lang defaultLang) {
        super(defaultLang);
    }

    /**
     * Prepares an RDF writer
     *
     * @param lang Language to use for the output serialization, if {@code null} defaults to the default language
     * @return RDF writer
     */
    protected RDFWriterBuilder prepareWriter(Lang lang) {
        return RDFWriterBuilder.create().lang(lang != null ? lang : this.defaultLang);
    }

    @Override
    public byte[] serialize(String topic, Graph data) {
        if (data == null) {
            return new byte[0];
        }
        return serializeInternal(data, null);
    }

    @Override
    public byte[] serialize(String topic, Headers headers, Graph data) {
        if (data == null) {
            return new byte[0];
        }

        String contentType = findContentType(headers);
        Lang lang = StringUtils.isNotBlank(contentType) ? RDFLanguages.contentTypeToLang(contentType) : null;
        return serializeInternal(data, lang);
    }

    /**
     * Serializes the dataset graph to a byte sequence
     *
     * @param data Dataset graph
     * @param lang Language, if {@code null} then the serializers default language is used
     * @return Serialized dataset graph
     */
    protected byte[] serializeInternal(Graph data, Lang lang) {
        ByteArrayOutputStream output = new ByteArrayOutputStream();
        prepareWriter(lang).source(data).output(output);
        return output.toByteArray();
    }
}