[BEANUTILS-244] [collections] Add a multi property beancomparator

• Type: New Feature
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Fix Version/s: 2.0.0
• Component/s: Bean-Collections

Environment

Operating System: Windows XP
Platform: All

• Bugzilla Id: 39008
• Assignee: Unassigned
• Reporter: Baptiste MATHUS
• Created: 17/Mar/06 16:12
• Updated: 05/Dec/13 21:05

Description

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)

{ 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.equals(comp.comparatorList.get))

{ 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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