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Java > Open Source Codes > org > apache > ojb > broker > accesslayer > PagingIterator


1 package org.apache.ojb.broker.accesslayer;
2
3 /* Copyright 2003-2005 The Apache Software Foundation
4  *
5  * Licensed under the Apache License, Version 2.0 (the "License");
6  * you may not use this file except in compliance with the License.
7  * You may obtain a copy of the License at
8  *
9  * http://www.apache.org/licenses/LICENSE-2.0
10  *
11  * Unless required by applicable law or agreed to in writing, software
12  * distributed under the License is distributed on an "AS IS" BASIS,
13  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14  * See the License for the specific language governing permissions and
15  * limitations under the License.
16  */
17
18 import org.apache.ojb.broker.PersistenceBrokerException;
19 import org.apache.ojb.broker.query.Query;
20
21 /**
22  * PagingIterator is wrapper around an OJBIterator to support startAt endAt
23  * positions. The PagingIterator returns rows <b>including</b> startAt
24  * and <b>including</b> endAt.
25  *
26  * startAt = 1, endAt = 11 returns rows 1 to 11 if available
27  * if endAt == Query.NO_END_AT_INDEX endAt is set to the last available row
28  *
29  * @author <a HREF="mailto:jbraeuchi@gmx.ch">Jakob Braeuchi</a>
30  * @version $Id: PagingIterator.java,v 1.10.2.2 2005/12/21 22:22:58 tomdz Exp $
31  */
32 public class PagingIterator implements OJBIterator
33 {
34     private final OJBIterator m_iterator;
35     private int m_startAt;
36     private int m_endAt;
37     private int m_rowLimit;
38     private int m_fullSize;
39     private int m_currentCursorPosition; // position of the wrapped iterator
40
41     /**
42      * Constructor
43      * @param anIterator wrapped Iterator
44      * @param startAt (first row is 1)
45      * @param endAt (Query.NO_END_AT_INDEX stands for all available rows)
46      */
47     public PagingIterator(OJBIterator anIterator, int startAt, int endAt)
48     {
49         super();
50
51         if (endAt != Query.NO_START_AT_INDEX && startAt > endAt)
52         {
53             throw new PersistenceBrokerException("startAt must be less than endAt.");
54         }
55
56         m_iterator = anIterator;
57         m_fullSize = m_iterator.size();
58
59         if (startAt == Query.NO_START_AT_INDEX)
60         {
61             m_startAt = 1;
62         }
63         else
64         {
65             m_startAt = startAt;
66         }
67
68         if (endAt == Query.NO_END_AT_INDEX)
69         {
70             m_endAt = m_fullSize;
71         }
72         else
73         {
74             m_endAt = Math.min(endAt, m_fullSize);
75         }
76         
77         m_rowLimit = Math.max(0, m_endAt - m_startAt + 1);
78         m_currentCursorPosition = m_startAt - 1;
79
80         m_iterator.absolute(m_currentCursorPosition);
81     }
82
83     /**
84      * @see org.apache.ojb.broker.accesslayer.OJBIterator#size()
85      */
86     public int size() throws PersistenceBrokerException
87     {
88         if (m_fullSize < m_rowLimit)
89         {
90             return m_fullSize;
91         }
92         else
93         {
94             return m_rowLimit;
95         }
96     }
97
98     /**
99      * @see org.apache.ojb.broker.accesslayer.OJBIterator#fullSize()
100      */
101     public int fullSize() throws PersistenceBrokerException
102     {
103         return m_fullSize;
104     }
105     
106     /**
107      * @see org.apache.ojb.broker.accesslayer.OJBIterator#absolute(int)
108      */
109     public boolean absolute(int row) throws PersistenceBrokerException
110     {
111         int newPosition = (m_startAt - 1) + row;
112         
113         if (newPosition < m_startAt)
114         {
115             newPosition = Math.max(m_endAt + row, m_startAt - 1);
116         }
117         
118         if (newPosition > m_endAt)
119         {
120             newPosition = m_endAt;
121         }
122         
123         m_currentCursorPosition = newPosition;
124         return m_iterator.absolute(newPosition);
125     }
126
127     /**
128      * @see org.apache.ojb.broker.accesslayer.OJBIterator#relative(int)
129      */
130     public boolean relative(int row) throws PersistenceBrokerException
131     {
132         return absolute(m_currentCursorPosition - (m_startAt - 1) + row);
133     }
134
135     /**
136      * @see org.apache.ojb.broker.accesslayer.OJBIterator#releaseDbResources()
137      */
138     public void releaseDbResources()
139     {
140         m_iterator.releaseDbResources();
141     }
142
143     /**
144      * remove is not supported
145      */
146     public void remove()
147     {
148         throw new UnsupportedOperationException JavaDoc("remove not supported by PagingIterator");
149     }
150
151     /**
152      * @see java.util.Iterator#hasNext()
153      */
154     public boolean hasNext()
155     {
156         if (m_currentCursorPosition < m_endAt)
157         {
158             return true;
159         }
160         else
161         {
162             releaseDbResources();
163             return false;
164         }
165
166     }
167
168     /**
169      * @see java.util.Iterator#next()
170      */
171     public Object JavaDoc next()
172     {
173         m_currentCursorPosition++;
174         return m_iterator.next();
175     }
176
177     /**
178      * @see org.apache.ojb.broker.accesslayer.OJBIterator#disableLifeCycleEvents()
179      */
180     public void disableLifeCycleEvents()
181     {
182         m_iterator.disableLifeCycleEvents();
183     }
184 }
185
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