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From "Ganesh Gowtham (JIRA)" <j...@apache.org>
Subject [jira] Commented: (BEANUTILS-244) [collections] Add a multi property beancomparator
Date Tue, 01 Sep 2009 08:23:33 GMT

    [ https://issues.apache.org/jira/browse/BEANUTILS-244?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12749810#action_12749810
] 

Ganesh Gowtham commented on BEANUTILS-244:
------------------------------------------

HI MATHUS , 

i had done same stuff in very simple manner 

[Code Sample | http://sites.google.com/site/ganeshgowtham/Home/submissions/multigenericcomparator-using-apache-commons---ganesh-gowtham]

                      / **
	 *
	 * @param <T>
	 * @param list
	 * @param beanPropertyNames ( array of bean properties on which sorting should happend )
	 * @param isAscending ( if true sorts on ascending order, false sorts on desending order)
	 */
	public static <T> void sort(List<T> list, boolean isAscending,String... beanPropertyNames)

                   {
		        Collection<Comparator<T>> beanComparatorCollection = new  ArrayList<Comparator<T>>(beanPropertyNames.length);

		for(int i =0;i<beanPropertyNames.length;i++)
		{
			beanComparatorCollection.add(new BeanComparator(beanPropertyNames[i]));
		}

		Comparator<T> finalComparator = ComparatorUtils.chainedComparator(beanComparatorCollection);

		if (!isAscending) {
			finalComparator = new ReverseComparator(finalComparator);
		}

		Collections.sort(list, finalComparator);
	}

Hi Folks , Let me know your views !!!

> [collections] Add a multi property beancomparator
> -------------------------------------------------
>
>                 Key: BEANUTILS-244
>                 URL: https://issues.apache.org/jira/browse/BEANUTILS-244
>             Project: Commons BeanUtils
>          Issue Type: New Feature
>          Components: Bean-Collections
>         Environment: Operating System: Windows XP
> Platform: All
>            Reporter: Baptiste MATHUS
>            Priority: Minor
>             Fix For: LATER THAN 1.8.1
>
>
> Hi,
> I recently needed to be able to sort a list of beans on many properties. So I
> thought I would try and pick one of the collections comparators.
> I had to to the sorting close to the sql way : be able to sort on n properties,
> some ascending, some descending.
> I haven't found what I'm looking for (:p), but I found some comparators in the
> commons I used to do this : I used BeanComparator, NullComparator and
> ComparatorChain to create a class : MultiPropertyBeanComparator.
> Is there already something in one of the commons package that could be used
> instead of it ? 
> If not, I'd be glad to contribute the small piece of code if wanted. It has
> dependencies against commons-beanutils (BeanComparator, which is moving from one
> package to another at the moment, no ?) and commons-lang
> (StringUtils.isBlank()). I think some things might not satisfactory for
> everybody, but hey, could still be improved without problems, that's not big
> work :p.
> As adviced on the user mailing list, I'm posting the code on this bugzilla, so
> as maybe one of the coder could take a look at it.
> Here it is :
> =======================================
> import java.io.Serializable;
> import java.util.ArrayList;
> import java.util.Comparator;
> import java.util.List;
> import org.apache.commons.beanutils.BeanComparator;
> import org.apache.commons.collections.ComparatorUtils;
> import org.apache.commons.collections.comparators.NullComparator;
> import org.apache.commons.collections.comparators.ReverseComparator;
> import org.apache.commons.lang.StringUtils;
> /**
>  * This comparator lets you sort a list using a list of properties. You can
> specify ascending or
>  * descending order on these properties.
>  * <p>
>  * For example, if you want to sort with natural order a list of beans with
> properties firstname,
>  * nickname and address, sorting the firstname descending, you can do it this way:
>  * </p>
>  * <code>List l = ...</code>
>  * <code>...</code>
>  * <code>MultiPropertyBeanComparator multiPropBeanComp = new
> MultiPropertyBeanComparator();</code>
>  * <code>multiPropBeanComp.append("firstname",
> true).append("nickname").append("address");</code>
>  * <code>Collections.sort(l,multiPropBeanComp);</code>
>  * 
>  * @author Baptiste MATHUS
>  */
> public class MultiPropertyBeanComparator implements Comparator, Serializable
> {
> 	private static final long serialVersionUID = -1431852774261001458L;
> 	private List comparatorList = new ArrayList();
> 	/**
> 	 * Use this method to add a comparator to the list.
> 	 * 
> 	 * @param property
> 	 *            the property on which to apply the given comparator.
> 	 * @param comparator
> 	 *            the comparator to be added. If null, natural order will be used.
> 	 * @param reverse
> 	 *            <p>
> 	 *            must be true if the given comparator must be used in opposite
> order to sort. For
> 	 *            example, if the comparator is designed to sort in ascending
> order, put this
> 	 *            parameter to <code>true</code> if you want descending order.
> 	 *            </p>
> 	 *            <p>
> 	 *            If the comparator is null, then the reversed natural order is used.
> 	 *            </p>
> 	 */
> 	public MultiPropertyBeanComparator append(String property, Comparator comparator,
> 			boolean reverse)
> 	{
> 		if (StringUtils.isBlank(property))
> 		{
> 			throw new IllegalArgumentException("The given property is blank");
> 		}
> 		// If the comparator is null, then compare only on the given property
> 		// with a natural sort.
> 		if (comparator == null)
> 		{
> 			comparator = new BeanComparator(property, new NullComparator(false));
> 		}
> 		// Else : compare on the property, but with given comparator.
> 		else
> 		{
> 			comparator = new BeanComparator(property, comparator);
> 		}
> 		// Here, the comparator cannot be null anymore, so reverse it if
> 		// necessary.
> 		if (reverse)
> 		{
> 			comparator = new ReverseComparator(comparator);
> 		}
> 		comparatorList.add(comparator);
> 		return this;
> 	}
> 	public MultiPropertyBeanComparator append(String property, Comparator c)
> 	{
> 		return append(property, c, false);
> 	}
> 	public MultiPropertyBeanComparator append(String property)
> 	{
> 		return append(property, null, false);
> 	}
> 	public MultiPropertyBeanComparator append(String property, boolean reverse)
> 	{
> 		return append(property, null, reverse);
> 	}
> 	/**
> 	 * Use this method to clear the
> 	 */
> 	public void clear()
> 	{
> 		comparatorList.clear();
> 	}
> 	/**
> 	 * Considered to be equal when all properties and comparators equal.
> 	 * 
> 	 * @see java.lang.Object#equals(java.lang.Object)
> 	 * @overrides
> 	 */
> 	public boolean equals(Object obj)
> 	{
> 		MultiPropertyBeanComparator comp = (MultiPropertyBeanComparator) obj;
> 		if (this.comparatorList.size() != comp.comparatorList.size())
> 		{
> 			return false;
> 		}
> 		for (int i = 0; i < comparatorList.size(); ++i)
> 		{
> 			if (!this.comparatorList.get(i).equals(comp.comparatorList.get(i)))
> 			{
> 				return false;
> 			}
> 		}
> 		return true;
> 	}
> 	/**
> 	 * @see Comparator#compare(T, T)
> 	 * @overrides
> 	 */
> 	public int compare(Object arg0, Object arg1)
> 	{
> 		return getComparator().compare(arg0, arg1);
> 	}
> 	private Comparator getComparator()
> 	{
> 		return ComparatorUtils.chainedComparator(comparatorList);
> 	}
> }
> =============

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