hbase-client/src/main/java/org/apache/hadoop/hbase/util/Writables.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.hadoop.hbase.util;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import org.apache.hadoop.io.DataInputBuffer;
import org.apache.hadoop.io.Writable;
import org.apache.yetus.audience.InterfaceAudience;

/**
 * Utility class with methods for manipulating Writable objects
 */
@InterfaceAudience.Private
public class Writables {
  /**
   * Get the Writable's contents as a byte array
   * @param w writable
   * @return The bytes of <code>w</code> gotten by running its
   *         {@link Writable#write(java.io.DataOutput)} method.
   * @throws IOException e
   * @see #getWritable(byte[], Writable)
   */
  public static byte[] getBytes(final Writable w) throws IOException {
    if (w == null) {
      throw new IllegalArgumentException("Writable cannot be null");
    }
    ByteArrayOutputStream byteStream = new ByteArrayOutputStream();
    DataOutputStream out = new DataOutputStream(byteStream);
    try {
      w.write(out);
      out.close();
      out = null;
      return byteStream.toByteArray();
    } finally {
      if (out != null) {
        out.close();
      }
    }
  }

  /**
   * Put a bunch of Writables as bytes all into the one byte array.
   * @param ws writable
   * @return The bytes of <code>w</code> gotten by running its
   *         {@link Writable#write(java.io.DataOutput)} method.
   * @throws IOException e
   */
  public static byte[] getBytes(final Writable... ws) throws IOException {
    List<byte[]> bytes = new ArrayList<>(ws.length);
    int size = 0;
    for (Writable w : ws) {
      byte[] b = getBytes(w);
      size += b.length;
      bytes.add(b);
    }
    byte[] result = new byte[size];
    int offset = 0;
    for (byte[] b : bytes) {
      System.arraycopy(b, 0, result, offset, b.length);
      offset += b.length;
    }
    return result;
  }

  /**
   * Set bytes into the passed Writable by calling its
   * {@link Writable#readFields(java.io.DataInput)}.
   * @param bytes serialized bytes
   * @param w     An empty Writable (usually made by calling the null-arg constructor).
   * @return The passed Writable after its readFields has been called fed by the passed
   *         <code>bytes</code> array or IllegalArgumentException if passed null or an empty
   *         <code>bytes</code> array.
   * @throws IOException e
   */
  public static Writable getWritable(final byte[] bytes, final Writable w) throws IOException {
    return getWritable(bytes, 0, bytes.length, w);
  }

  /**
   * Set bytes into the passed Writable by calling its
   * {@link Writable#readFields(java.io.DataInput)}.
   * @param bytes  serialized bytes
   * @param offset offset into array
   * @param length length of data
   * @param w      An empty Writable (usually made by calling the null-arg constructor).
   * @return The passed Writable after its readFields has been called fed by the passed
   *         <code>bytes</code> array or IllegalArgumentException if passed null or an empty
   *         <code>bytes</code> array.
   * @throws IOException e
   */
  public static Writable getWritable(final byte[] bytes, final int offset, final int length,
    final Writable w) throws IOException {
    if (bytes == null || length <= 0) {
      throw new IllegalArgumentException("Can't build a writable with empty " + "bytes array");
    }
    if (w == null) {
      throw new IllegalArgumentException("Writable cannot be null");
    }
    DataInputBuffer in = new DataInputBuffer();
    try {
      in.reset(bytes, offset, length);
      w.readFields(in);
      return w;
    } finally {
      in.close();
    }
  }

  /**
   * Copy one Writable to another. Copies bytes using data streams.
   * @param src Source Writable
   * @param tgt Target Writable
   * @return The target Writable.
   * @throws IOException e
   */
  public static Writable copyWritable(final Writable src, final Writable tgt) throws IOException {
    return copyWritable(getBytes(src), tgt);
  }

  /**
   * Copy one Writable to another. Copies bytes using data streams.
   * @param bytes Source Writable
   * @param tgt   Target Writable
   * @return The target Writable.
   * @throws IOException e
   */
  public static Writable copyWritable(final byte[] bytes, final Writable tgt) throws IOException {
    DataInputStream dis = new DataInputStream(new ByteArrayInputStream(bytes));
    try {
      tgt.readFields(dis);
    } finally {
      dis.close();
    }
    return tgt;
  }
}