WritableUtils.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.openflamingo.mapreduce.util;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.util.ReflectionUtils;

import java.io.*;
import java.util.ArrayList;
import java.util.List;

/**
 * Helper static methods for working with Writable objects.
 */
public class WritableUtils {

	/**
	 * Read fields from byteArray to a Writeable object.
	 *
	 * @param byteArray      Byte array to find the fields in.
	 * @param writableObject Object to fill in the fields.
	 */
	public static void readFieldsFromByteArray(byte[] byteArray, Writable writableObject) {
		DataInputStream inputStream = new DataInputStream(new ByteArrayInputStream(byteArray));
		try {
			writableObject.readFields(inputStream);
		} catch (IOException e) {
			throw new IllegalStateException("readFieldsFromByteArray: IOException", e);
		}
	}

	/**
	 * Write object to a byte array.
	 *
	 * @param writableObject Object to write from.
	 * @return Byte array with serialized object.
	 */
	public static byte[] writeToByteArray(Writable writableObject) {
		ByteArrayOutputStream outputStream =
			new ByteArrayOutputStream();
		DataOutput output = new DataOutputStream(outputStream);
		try {
			writableObject.write(output);
		} catch (IOException e) {
			throw new IllegalStateException("writeToByteArray: IOStateException", e);
		}
		return outputStream.toByteArray();
	}

	/**
	 * Write list of object to a byte array.
	 *
	 * @param writableList List of object to write from.
	 * @return Byte array with serialized objects.
	 */
	public static byte[] writeListToByteArray(
		List<? extends Writable> writableList) {
		ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
		DataOutput output = new DataOutputStream(outputStream);
		try {
			output.writeInt(writableList.size());
			for (Writable writable : writableList) {
				writable.write(output);
			}
		} catch (IOException e) {
			throw new IllegalStateException(
				"writeListToByteArray: IOException", e);
		}
		return outputStream.toByteArray();
	}

	/**
	 * Read fields from byteArray to a list of Writeable objects.
	 *
	 * @param byteArray     Byte array to find the fields in.
	 * @param writableClass Class of the objects to instantiate.
	 * @param conf          Configuration used for instantiation (i.e Configurable)
	 * @return List of writable objects.
	 */
	public static List<? extends Writable> readListFieldsFromByteArray(
		byte[] byteArray,
		Class<? extends Writable> writableClass,
		Configuration conf) {
		try {
			DataInputStream inputStream =
				new DataInputStream(new ByteArrayInputStream(byteArray));
			int size = inputStream.readInt();
			List<Writable> writableList = new ArrayList<Writable>(size);
			for (int i = 0; i < size; ++i) {
				Writable writable =
					ReflectionUtils.newInstance(writableClass, conf);
				writable.readFields(inputStream);
				writableList.add(writable);
			}
			return writableList;
		} catch (IOException e) {
			throw new IllegalStateException(
				"readListFieldsFromZnode: IOException", e);
		}
	}
}