-
Type:
New Feature
-
Status: Open
-
Priority:
Minor
-
Resolution: Unresolved
-
Affects Version/s: None
-
Fix Version/s: 2.0.0
-
Component/s: Bean-Collections
-
Labels:None
-
Environment:
Operating System: Windows XP
Platform: All
-
Bugzilla Id:39008
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 (), 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 .
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)
// Else : compare on the property, but with given comparator.
else
// Here, the comparator cannot be null anymore, so reverse it if
// necessary.
if (reverse)
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.equals(comp.comparatorList.get
))
}
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); }}
=============