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.i18n.I18n;
026    import org.apache.directory.shared.ldap.schema.LdapComparator;
027    import org.slf4j.Logger;
028    import org.slf4j.LoggerFactory;
029    
030    
031    /**
032     * Compares two objects taking into account that one might be a Comparable.
033     * 
034     * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
035     * @version $Rev: 912436 $
036     */
037    public class ComparableComparator<T> extends LdapComparator<Comparable<T>>
038    {
039        /** A logger for this class */
040        private static final Logger LOG = LoggerFactory.getLogger( ComparableComparator.class );
041    
042        /** The serialVersionUID */
043        private static final long serialVersionUID = 1L;
044    
045        /**
046         * The BooleanComparator constructor. Its OID is the BooleanMatch matching
047         * rule OID.
048         */
049        public ComparableComparator( String oid )
050        {
051            super( oid );
052        }
053    
054        /**
055         * Compares two objects taking into account that one may be a Comparable. If
056         * the first is a comparable then its compareTo operation is called and the
057         * result returned as is. If the first is not a Comparable but the second is
058         * then its compareTo method is called and the result is returned after
059         * being negated. If none are comparables the hashCode of o1 minus the
060         * hashCode of o2 is returned.
061         * 
062         * @see Comparator#compare(Object, Object)
063         */
064        public int compare( Comparable<T> o1, Comparable<T> o2 )
065        {
066            LOG.debug( "comparing objects '{}' with '{}'", o1, o2 );
067            
068            if ( ( o1 == null ) && ( o2 == null ) )
069            {
070                return 0;
071            }
072            
073            if ( o1 instanceof Comparable<?> )
074            {
075                if ( o2 == null )
076                {
077                    return -1;
078                }
079                else
080                {
081                    return o1.compareTo( ( T ) o2 );
082                }
083            }
084    
085            if ( o2 == null )
086            {
087                return 1;
088            }
089            else if ( o2 instanceof Comparable<?> )
090            {
091                if ( o1 == null )
092                {
093                    return -1;
094                }
095                else
096                {
097                    return - o2.compareTo( ( T ) o1 );
098                }
099            }
100    
101            // before https://issues.apache.org/jira/browse/DIRSERVER-928 it was
102            // return o1.hashCode() - o2.hashCode();
103            
104            // now we will blow a stack trace if none of the objects are Comparable
105            throw new IllegalArgumentException( I18n.err( I18n.ERR_04217, o1, o2 ) );
106        }
107    }