cdmlib-services/src/main/java/eu/etaxonomy/cdm/api/service/pager/PagerUtils.java

   1 /**
   2 * Copyright (C) 2012 EDIT
   3 * European Distributed Institute of Taxonomy
   4 * http://www.e-taxonomy.eu
   5 *
   6 * The contents of this file are subject to the Mozilla Public License Version 1.1
   7 * See LICENSE.TXT at the top of this package for the full license terms.
   8 */
   9 package eu.etaxonomy.cdm.api.service.pager;
  10
  11 import java.util.List;
  12
  13 import eu.etaxonomy.cdm.api.service.pager.impl.AbstractPagerImpl;
  14
  15 /**
  16  * @see also class <code>eu.etaxonomy.cdm.remote.controller.util.PagerParameter</code>
  17  *
  18  * @author a.kohlbecker
  19  \* @since Dec 10, 2012
  20  *
  21  */
  22 public class PagerUtils {
  23
  24     /**
  25      * Returns the start index for the given page size and page index values
  26      * by multiplying both values (startFor = pageSize * pageIndex).<BR>
  27      * If page size is <code>null</code>, either <code>null</code> is returned
  28      * or an exception is thrown if page index is > 0.
  29      * If page index is null it is assumed as 0.
  30      *
  31      * @param pageSize the page size
  32      * @param pageIndex the page index
  33      * @return the start index
  34      * @throws PagerRangeException if pageSize == null and pageIndex > 0
  35      */
  36     public static Integer startFor(Integer pageSize, Integer pageIndex) throws PagerRangeException {
  37         if(pageIndex == null) {
  38             pageIndex = 0;
  39         }
  40         if(pageSize == null){
  41             if (pageIndex > 0 ){
  42                 throw new PagerRangeException("Page index must be undefined or 0 for undefined page size but was " + pageIndex);
  43             }else{
  44                 return null;
  45             }
  46         }
  47         return pageSize *  pageIndex;
  48     }
  49
  50     /**
  51      * Returns the limit value as used in SQL/HQL statements for the given
  52      * page size.<BR>
  53      * Earlier, for <code>null</code> the value 0 was returned but as
  54      * it was decided that pageSize = <code>null</code> should not set any limitation
  55      * it was changed to return value <code>null</code>. This way the current implementation
  56      * is the identity function and has no effect except for documentation.
  57      * <code>null</code> should be handled in dao-s or specialized code such as
  58      * {@link #pageList(List, Integer, Integer)}.
  59      *
  60      * @param pageSize
  61      * @return
  62      */
  63     public static Integer limitFor(Integer pageSize) {
  64         if(pageSize == null){
  65             return null;
  66         }else{
  67             return pageSize;
  68         }
  69     }
  70
  71     /**
  72      * The original method {@link AbstractPagerImpl#hasResultsInRange(Long, Integer, Integer)} is
  73      * hard to find, therefore this method has been wired also into this Utility class
  74      * this this is looked up more frequently.
  75      *
  76      * @param numberOfResults
  77      * @param pageIndex
  78      * @param pageSize
  79      * @return
  80      */
  81     public static boolean hasResultsInRange(Long numberOfResults, Integer pageIndex, Integer pageSize) {
  82         return AbstractPagerImpl.hasResultsInRange(numberOfResults, pageIndex, pageSize);
  83     }
  84
  85     /**
  86      * Returns a synchronized (sub)list of fullList which contains only the items
  87      * for the given page
  88      * @param fullList
  89      * @param pageIndex page index
  90      * @param pageSize page size
  91      * @return a synchronized list holding the page items
  92      */
  93     public  static  <T extends Object> List<T> pageList(List<T> fullList, Integer pageIndex, Integer pageSize ){
  94         Integer start = startFor(pageSize, pageIndex);
  95         if (start == null){
  96             return fullList;
  97         }
  98         Integer limit = limitFor(pageSize); //no effect and never null at this point due to startFor semantics
  99         limit = Math.min(Integer.MAX_VALUE - start, limit);
 100
 101         if (fullList.size() > start) {
 102             Integer toIndex = Math.min(fullList.size(), start + limit);
 103             return fullList.subList(start, toIndex);
 104         }else{
 105             return fullList.subList(fullList.size(), fullList.size()); //empty list
 106         }
 107     }
 108
 109 }