lang/java/reef-io/src/main/java/org/apache/reef/io/data/loading/impl/WritableSerializer.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.reef.io.data.loading.impl;

import org.apache.commons.codec.binary.Base64;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.util.ReflectionUtils;
import org.apache.reef.io.serialization.Codec;

import java.io.*;

/**
 * A serializer class that serializes {@link Writable}s
 * into String using the below {@link Codec} that
 * encodes and decodes {@link Writable}s
 * By default this stores the class name in the serialized
 * form so that the specific type can be instantiated on
 * de-serialization. However, this also needs the jobconf
 * to passed in while de-serialization
 */
public final class WritableSerializer {
  public static <E extends Writable> String serialize(final E writable) {
    final WritableCodec<E> writableCodec = new WritableCodec<>();
    return Base64.encodeBase64String(writableCodec.encode(writable));
  }

  public static <E extends Writable> E deserialize(final String serializedWritable) {
    final WritableCodec<E> writableCodec = new WritableCodec<>();
    return writableCodec.decode(Base64.decodeBase64(serializedWritable));
  }

  public static <E extends Writable> E deserialize(final String serializedWritable, final JobConf jobConf) {
    final WritableCodec<E> writableCodec = new WritableCodec<>(jobConf);
    return writableCodec.decode(Base64.decodeBase64(serializedWritable));
  }

  static class WritableCodec<E extends Writable> implements Codec<E> {
    private final JobConf jobConf;

    WritableCodec(final JobConf jobConf) {
      this.jobConf = jobConf;
    }

    WritableCodec() {
      this.jobConf = new JobConf();
    }

    @Override
    public E decode(final byte[] bytes) {
      final ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
      try (DataInputStream dais = new DataInputStream(bais)) {
        final String className = dais.readUTF();
        final E writable = (E) ReflectionUtils.newInstance(Class.forName(className), jobConf);
        writable.readFields(dais);
        return writable;
      } catch (final IOException e) {
        throw new RuntimeException("Could not de-serialize JobConf", e);
      } catch (final ClassNotFoundException e) {
        throw new RuntimeException("Could not instantiate specific writable class", e);
      }
    }

    @Override
    public byte[] encode(final E writable) {
      final ByteArrayOutputStream baos = new ByteArrayOutputStream();
      try (DataOutputStream daos = new DataOutputStream(baos)) {
        daos.writeUTF(writable.getClass().getName());
        writable.write(daos);
        return baos.toByteArray();
      } catch (final IOException e) {
        throw new RuntimeException("Could not serialize JobConf", e);
      }
    }
  }

  /**
   * Empty private constructor to prohibit instantiation of utility class.
   */
  private WritableSerializer() {
  }
}