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Java > Open Source Codes > org > displaytag > util > CollectionUtil


1 /**
2  * Licensed under the Artistic License; you may not use this file
3  * except in compliance with the License.
4  * You may obtain a copy of the License at
5  *
6  * http://displaytag.sourceforge.net/license.html
7  *
8  * THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR
9  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
10  * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
11  */
12 package org.displaytag.util;
13
14 import java.util.ArrayList JavaDoc;
15 import java.util.Iterator JavaDoc;
16 import java.util.List JavaDoc;
17
18 import org.apache.commons.collections.IteratorUtils;
19
20
21 /**
22  * Utility methods for collection handling.
23  * @author Fabrizio Giustina
24  * @version $Revision: 720 $ ($Author: fgiust $)
25  */
26 public final class CollectionUtil
27 {
28
29     /**
30      * Don't instantiate a CollectionUtil.
31      */
32     private CollectionUtil()
33     {
34         // unused
35 }
36
37     /**
38      * Create a list of objects taken from the given iterator and crop the resulting list according to the startIndex
39      * and numberOfItems parameters.
40      * @param iterator Iterator
41      * @param startIndex int starting index
42      * @param numberOfItems int number of items to keep in the list
43      * @return List with values taken from the given object, cropped according to startIndex and numberOfItems
44      * parameters
45      */
46     private static List JavaDoc getSubList(Iterator JavaDoc iterator, int startIndex, int numberOfItems)
47     {
48
49         List JavaDoc croppedList = new ArrayList JavaDoc(numberOfItems);
50
51         int skippedRecordCount = 0;
52         int copiedRecordCount = 0;
53         while (iterator.hasNext())
54         {
55
56             Object JavaDoc object = iterator.next();
57
58             if (++skippedRecordCount <= startIndex)
59             {
60                 continue;
61             }
62
63             croppedList.add(object);
64
65             if ((numberOfItems != 0) && (++copiedRecordCount >= numberOfItems))
66             {
67                 break;
68             }
69         }
70
71         return croppedList;
72
73     }
74
75     /**
76      * create an iterator on a given object (Collection, Enumeration, array, single Object) and crop the resulting list
77      * according to the startIndex and numberOfItems parameters.
78      * @param iterableObject Collection, Enumeration or array to crop
79      * @param startIndex int starting index
80      * @param numberOfItems int number of items to keep in the list
81      * @return List with values taken from the given object, cropped according the startIndex and numberOfItems
82      * parameters
83      */
84     public static List JavaDoc getListFromObject(Object JavaDoc iterableObject, int startIndex, int numberOfItems)
85     {
86         if (iterableObject instanceof List JavaDoc)
87         {
88             // easier, use sublist
89 List JavaDoc list = ((List JavaDoc) iterableObject);
90
91             // check for partial lists
92 int lastRecordExclusive = numberOfItems <= 0 ? list.size() : startIndex + numberOfItems;
93             if (lastRecordExclusive > list.size())
94             {
95                 lastRecordExclusive = list.size();
96             }
97
98             if (startIndex < list.size())
99             {
100                 return list.subList(startIndex, lastRecordExclusive);
101             }
102         }
103
104         // use an iterator
105 Iterator JavaDoc iterator = IteratorUtils.getIterator(iterableObject);
106         return getSubList(iterator, startIndex, numberOfItems);
107     }
108 }
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