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,
013 * software distributed under the License is distributed on an
014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 * KIND, either express or implied. See the License for the
016 * specific language governing permissions and limitations
017 * under the License.
018 *
019 */
020 package org.apache.directory.shared.ldap.schema.comparators;
021
022
023 import java.util.Comparator;
024
025 import org.apache.directory.shared.ldap.csn.Csn;
026
027
028 /**
029 * A comparator for CSN.
030 *
031 * The CSN are ordered depending on an evaluation of its component, in this order :
032 * - time,
033 * - changeCount,
034 * - sid
035 * - modifierNumber
036 *
037 * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
038 * @version $Rev$
039 */
040 public class CsnComparator implements Comparator<String>
041 {
042 /** A static instance of this comparator */
043 public static final Comparator<String> INSTANCE = new CsnComparator();
044
045
046 /**
047 * @see java.util.Comparator#compare(java.lang.Object, java.lang.Object)
048 */
049 public int compare( String csnStr1, String csnStr2 )
050 {
051 // -------------------------------------------------------------------
052 // Handle some basis cases
053 // -------------------------------------------------------------------
054
055 if ( csnStr1 == null )
056 {
057 return ( csnStr2 == null ) ? 0 : -1;
058 }
059
060 if ( csnStr2 == null )
061 {
062 return 1;
063 }
064
065 Csn csn1 = new Csn( csnStr1 );
066 Csn csn2 = new Csn( csnStr2 );
067
068 if ( csn1.getTimestamp() != csn2.getTimestamp() )
069 {
070 return ( csn1.getTimestamp() < csn2.getTimestamp() ? -1 : 1 );
071 }
072
073 if ( csn1.getChangeCount() != csn2.getChangeCount() )
074 {
075 return ( csn1.getChangeCount() < csn2.getChangeCount() ? -1 : 1 );
076 }
077
078 if ( csn1.getReplicaId() != csn2.getReplicaId() )
079 {
080 return ( csn1.getReplicaId() < csn2.getReplicaId() ? -1 : 1 );
081 }
082
083 if ( csn1.getOperationNumber() != csn2.getOperationNumber() )
084 {
085 return ( csn1.getOperationNumber() < csn2.getOperationNumber() ? -1 : 1 );
086 }
087
088 return 0;
089 }
090 }