What about using a "chained" comparator? Wouldn't that do what you want?
Yes, it's not fun to set up, but you could create a helper method...
public void sort( List beans, String[] properties )
{
// Create a bean comparator for each property.
// Create a chained comparator from the bean comparators.
// Sort the list
...
}
-----Original Message-----
From: Stephen Colebourne [mailto:[EMAIL PROTECTED]
Sent: Thursday, March 16, 2006 7:06 PM
To: Jakarta Commons Users List
Subject: Re: [collections] [beanutils] Multi property BeanComparator
This is an interesting idea, to group multiple property comparisons in one.
It no longer fits in [collections] however as the bean code from
collections has moved to [beanutils] in their bean-collections jar.
The problem with beanutils is that it is not well maintained at the moment.
I recommend that you raise a bugzilla enhancement request for beanutils
and attach your code as a patch. That way the idea can be looked at when
someone has a chance.
Stephen
MATHUS Baptiste wrote:
> Hi everybody,
>
> 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 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.
>
> 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);
> }
> }
> =======================================
>
> Thanks for the answers.
>
> Baptiste
>
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