*
     * @param kryo the Kryo instance to register classes with
     */
    protected void registerClasses(final Kryo kryo) {
        // Primitive types and wrappers
        kryo.register(String.class);
        kryo.register(String[].class);
        kryo.register(Integer.class);
        kryo.register(int[].class);
        kryo.register(Long.class);
        kryo.register(long[].class);
        kryo.register(Double.class);

* It is ok for Serializer to be used as a replacement for Java serialization as a migration step.

import org.codelibs.fess.unit.UnitFessTestCase;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.TestInfo;

/**
 * Test class for DataSerializer.
 * Tests serialization and deserialization with Kryo and JavaBin.
 */
public class DataSerializerTest extends UnitFessTestCase {

    private DataSerializer serializer;

    @Override
    protected void setUp(TestInfo testInfo) throws Exception {

# Default script for the crawler (e.g., groovy).
crawler.default.script=groovy
# Number of threads for HTTP crawling.
crawler.http.thread_pool.size=0
# Serializer type for crawler data (e.g., kryo).
crawler.data.serializer=kryo
# Maximum length of site name in documents.
crawler.document.max.site.length=100
# Encoding for site names in documents.
crawler.document.site.encoding=UTF-8
# Hostname to use when unknown in documents.

			<artifactId>bcprov-jdk18on</artifactId>
			<version>${bouncycastle.version}</version>
		</dependency>
		<dependency>
			<groupId>com.esotericsoftware</groupId>
			<artifactId>kryo</artifactId>
			<version>${kryo.version}</version>
		</dependency>

		<!-- suggest library -->
		<dependency>
			<groupId>org.codelibs.fess</groupId>
			<artifactId>fess-suggest</artifactId>

     */
    Integer getCrawlerHttpThreadPoolSizeAsInteger();

    /**
     * Get the value for the key 'crawler.data.serializer'. <br>
     * The value is, e.g. kryo <br>
     * comment: Serializer type for crawler data (e.g., kryo).
     * @return The value of found property. (NotNull: if not found, exception but basically no way)
     */
    String getCrawlerDataSerializer();

    /**