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     */
018    package org.apache.hadoop.fs;
019    
020    import org.apache.commons.codec.binary.Base64;
021    import org.apache.commons.lang.builder.EqualsBuilder;
022    import org.apache.commons.lang.builder.HashCodeBuilder;
023    import org.apache.hadoop.classification.InterfaceAudience;
024    import 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
035    public 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    }