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From bugzi...@apache.org
Subject DO NOT REPLY [Bug 39008] New: - Add a multi property beancomparator
Date Fri, 17 Mar 2006 08:12:20 GMT
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http://issues.apache.org/bugzilla/show_bug.cgi?id=39008

           Summary: Add a multi property beancomparator
           Product: Commons
           Version: unspecified
          Platform: All
        OS/Version: Windows XP
            Status: NEW
          Severity: enhancement
          Priority: P3
         Component: Collections
        AssignedTo: commons-dev@jakarta.apache.org
        ReportedBy: mathus.b@mipih.fr


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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