OrderedDropDownChoice.java

import java.text.Collator;
import java.util.Comparator;
import java.util.List;
import java.util.Locale;

import org.apache.wicket.Session;
import org.apache.wicket.markup.html.form.DropDownChoice;
import org.apache.wicket.markup.html.form.IChoiceRenderer;
import org.apache.wicket.model.IModel;

import com.google.common.collect.Ordering;

/**
 * DropDownChoice which sort its choices (or in HTML's terminology select's options) according it's localized value
 * and using current locale based Collator so it's sorted how it should be in particular language (ie. including national characters, 
 * using right order).
 * 
 * @author Michal Bernhard [email protected] 2013
 *
 * @param <T>
 */
public class OrderedDropDownChoice<T> extends DropDownChoice<T> {

	public OrderedDropDownChoice(String id, IModel<? extends List<? extends T>> choices, IChoiceRenderer<? super T> renderer) {
		super(id, choices, renderer);
	}

	public OrderedDropDownChoice(String id, IModel<? extends List<? extends T>> choices) {
		super(id, choices);
	}
	
	public OrderedDropDownChoice(String id) {
		super(id);
	}
	
	public OrderedDropDownChoice(
			String id,
			IModel<T> model,
			IModel<? extends List<? extends T>> choices,
					IChoiceRenderer<? super T> renderer) {
		
		super(id, model, choices, renderer);
	}
	
	@Override
	public List<? extends T> getChoices() {
		List<? extends T> unsortedChoices = super.getChoices();
		List<? extends T> sortedChoices = Ordering.from(displayValueAlphabeticComparator()).sortedCopy(unsortedChoices);
		
		return sortedChoices;
	}

	private Collator localeBasedTertiaryCollator() {
		Locale currentLocale = Session.get().getLocale();
		Collator collator = Collator.getInstance(currentLocale);
		collator.setStrength(Collator.TERTIARY);
		
		return collator;
	}
	
	private Comparator<T> displayValueAlphabeticComparator() {
		
		final IChoiceRenderer<? super T> renderer = getChoiceRenderer();
		
		return new Comparator<T>() {

			@Override
			public int compare(T o1, T o2) {
				Object o1DisplayValue = renderer.getDisplayValue(o1);
				Object o2DisplayValue = renderer.getDisplayValue(o2);
				
				return localeBasedTertiaryCollator().compare(o1DisplayValue, o2DisplayValue);
			}
		};
		
	}
	

}