001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.hadoop.fs;
019
020import org.apache.commons.codec.binary.Base64;
021import org.apache.commons.lang.builder.EqualsBuilder;
022import org.apache.commons.lang.builder.HashCodeBuilder;
023import org.apache.hadoop.classification.InterfaceAudience;
024import org.apache.hadoop.classification.InterfaceStability;
025
026/**
027 * HDFS-specific volume identifier which implements {@link VolumeId}. Can be
028 * used to differentiate between the data directories on a single datanode. This
029 * identifier is only unique on a per-datanode basis.
030 * 
031 * Note that invalid IDs are represented by {@link VolumeId#INVALID_VOLUME_ID}.
032 */
033@InterfaceStability.Unstable
034@InterfaceAudience.Public
035public class HdfsVolumeId implements VolumeId {
036  
037  private final byte[] id;
038
039  public HdfsVolumeId(byte[] id) {
040    if (id == null) {
041      throw new NullPointerException("A valid Id can only be constructed " +
042                "with a non-null byte array.");
043    }
044    this.id = id;
045  }
046
047  @Override
048  public final boolean isValid() {
049    return true;
050  }
051
052  @Override
053  public int compareTo(VolumeId arg0) {
054    if (arg0 == null) {
055      return 1;
056    }
057    if (!arg0.isValid()) {
058      // any valid ID is greater 
059      // than any invalid ID: 
060      return 1;
061    }
062    return hashCode() - arg0.hashCode();
063  }
064
065  @Override
066  public int hashCode() {
067    return new HashCodeBuilder().append(id).toHashCode();
068  }
069
070  @Override
071  public boolean equals(Object obj) {
072    if (obj == null || obj.getClass() != getClass()) {
073      return false;
074    }
075    if (obj == this) {
076      return true;
077    }
078    HdfsVolumeId that = (HdfsVolumeId) obj;
079    // NB: if (!obj.isValid()) { return false; } check is not necessary
080    // because we have class identity checking above, and for this class
081    // isValid() is always true.
082    return new EqualsBuilder().append(this.id, that.id).isEquals();
083  }
084
085  @Override
086  public String toString() {
087    return Base64.encodeBase64String(id);
088  }
089}