flink-core/src/main/java/org/apache/flink/api/common/serialization/SimpleStringSchema.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.flink.api.common.serialization;

import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.api.common.typeinfo.BasicTypeInfo;
import org.apache.flink.api.common.typeinfo.TypeInformation;

import java.io.IOException;
import java.io.ObjectOutputStream;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;

import static org.apache.flink.util.Preconditions.checkNotNull;

/**
 * Very simple serialization schema for strings.
 *
 * <p>By default, the serializer uses "UTF-8" for string/byte conversion.
 */
@PublicEvolving
public class SimpleStringSchema implements DeserializationSchema<String>, SerializationSchema<String> {

	private static final long serialVersionUID = 1L;

	/** The charset to use to convert between strings and bytes.
	 * The field is transient because we serialize a different delegate object instead */
	private transient Charset charset;

	/**
	 * Creates a new SimpleStringSchema that uses "UTF-8" as the encoding.
	 */
	public SimpleStringSchema() {
		this(StandardCharsets.UTF_8);
	}

	/**
	 * Creates a new SimpleStringSchema that uses the given charset to convert between strings and bytes.
	 *
	 * @param charset The charset to use to convert between strings and bytes.
	 */
	public SimpleStringSchema(Charset charset) {
		this.charset = checkNotNull(charset);
	}

	/**
	 * Gets the charset used by this schema for serialization.
	 * @return The charset used by this schema for serialization.
	 */
	public Charset getCharset() {
		return charset;
	}

	// ------------------------------------------------------------------------
	//  Kafka Serialization
	// ------------------------------------------------------------------------

	@Override
	public String deserialize(byte[] message) {
		return new String(message, charset);
	}

	@Override
	public boolean isEndOfStream(String nextElement) {
		return false;
	}

	@Override
	public byte[] serialize(String element) {
		return element.getBytes(charset);
	}

	@Override
	public TypeInformation<String> getProducedType() {
		return BasicTypeInfo.STRING_TYPE_INFO;
	}

	// ------------------------------------------------------------------------
	//  Java Serialization
	// ------------------------------------------------------------------------

	private void writeObject (ObjectOutputStream out) throws IOException {
		out.defaultWriteObject();
		out.writeUTF(charset.name());
	}

	private void readObject(java.io.ObjectInputStream in) throws IOException, ClassNotFoundException {
		in.defaultReadObject();
		String charsetName = in.readUTF();
		this.charset = Charset.forName(charsetName);
	}
}