common/src/main/java/org/apache/nemo/common/coder/PairEncoderFactory.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.nemo.common.coder;

import org.apache.nemo.common.Pair;

import java.io.IOException;
import java.io.OutputStream;
import java.io.Serializable;

/**
 * An EncoderFactory for {@link Pair}. Reference: KvCoder in BEAM.
 *
 * @param <A> type for the left coder.
 * @param <B> type for the right coder.
 */
public final class PairEncoderFactory<A extends Serializable, B extends Serializable>
  implements EncoderFactory<Pair<A, B>> {
  private final EncoderFactory<A> leftEncoderFactory;
  private final EncoderFactory<B> rightEncoderFactory;

  /**
   * Private constructor of PairEncoderFactory class.
   *
   * @param leftEncoderFactory  coder for right element.
   * @param rightEncoderFactory coder for right element.
   */
  private PairEncoderFactory(final EncoderFactory<A> leftEncoderFactory,
                             final EncoderFactory<B> rightEncoderFactory) {
    this.leftEncoderFactory = leftEncoderFactory;
    this.rightEncoderFactory = rightEncoderFactory;
  }

  /**
   * static initializer of the class.
   *
   * @param leftEncoderFactory  left coder.
   * @param rightEncoderFactory right coder.
   * @param <A>                 type of the left element.
   * @param <B>                 type of the right element.
   * @return the new PairEncoderFactory.
   */
  public static <A extends Serializable, B extends Serializable> PairEncoderFactory<A, B>
  of(final EncoderFactory<A> leftEncoderFactory, final EncoderFactory<B> rightEncoderFactory) {
    return new PairEncoderFactory<>(leftEncoderFactory, rightEncoderFactory);
  }

  @Override
  public Encoder<Pair<A, B>> create(final OutputStream outputStream) throws IOException {
    return new PairEncoder<>(outputStream, leftEncoderFactory, rightEncoderFactory);
  }

  @Override
  public String toString() {
    final StringBuilder sb = new StringBuilder();
    sb.append("Pair(");
    sb.append(leftEncoderFactory.toString());
    sb.append(", ");
    sb.append(rightEncoderFactory.toString());
    sb.append(")");
    return sb.toString();
  }

  /**
   * PairEncoder.
   *
   * @param <T1> type for the left coder.
   * @param <T2> type for the right coder.
   */
  private final class PairEncoder<T1 extends Serializable, T2 extends Serializable> implements Encoder<Pair<T1, T2>> {

    private final Encoder<T1> leftEncoder;
    private final Encoder<T2> rightEncoder;

    /**
     * Constructor.
     *
     * @param outputStream        the output stream to store the encoded bytes.
     * @param leftEncoderFactory  the actual encoder to use for left elements.
     * @param rightEncoderFactory the actual encoder to use for right elements.
     * @throws IOException if fail to instantiate coders.
     */
    private PairEncoder(final OutputStream outputStream,
                        final EncoderFactory<T1> leftEncoderFactory,
                        final EncoderFactory<T2> rightEncoderFactory) throws IOException {
      this.leftEncoder = leftEncoderFactory.create(outputStream);
      this.rightEncoder = rightEncoderFactory.create(outputStream);
    }

    @Override
    public void encode(final Pair<T1, T2> pair) throws IOException {
      if (pair == null) {
        throw new IOException("cannot encode a null pair");
      }
      leftEncoder.encode(pair.left());
      rightEncoder.encode(pair.right());
    }
  }
}