Sample use of custom comparator in sorting a List<javax.faces.model.SelectItem> by the label, ascending. This is implemented inside a managed bean, fully registered in faces-config, with binding via EL in a sample XPage.

faces-config.xml

<?xml version="1.0" encoding="UTF-8"?>
<faces-config>
  <managed-bean>
    <managed-bean-name>myBean</managed-bean-name>
    <managed-bean-class>com.eric.test.SampleComparatorUse</managed-bean-class>
    <managed-bean-scope>session</managed-bean-scope>
  </managed-bean>
  <!--AUTOGEN-START-BUILDER: Automatically generated by IBM Domino Designer. Do not modify.-->
  <!--AUTOGEN-END-BUILDER: End of automatically generated section-->
</faces-config>

SampleComparatorUse.java

package com.eric.test;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

import javax.faces.model.SelectItem;

public class SampleComparatorUse implements Serializable {
	
	private static final long serialVersionUID = 1L;
	
	private String selectedOption;
	private List<SelectItem> selectOptionsList;
	
	public SampleComparatorUse() {}
	
	/**
	 * Custom Comparator, for use with sorting (ascending) a List<SelectItem>.
	 */
	private static class LabelAscComparator implements Comparator<SelectItem> {
		//uses a one-off cmoparison which returns comparison boolean, as int
		public int compare(SelectItem s1, SelectItem s2) {
		    //you can also do a case sensitive via s1.getLabel().compareTo(s2.getLabel())
			return s1.getLabel().compareToIgnoreCase(s2.getLabel());
		}
	}
	
	/**
	 * Getter for Combo Box options, sorted alphabetically ascending
	 * by the label. Read-only, as it's a computed value, so no setter.
	 */
	public List<SelectItem> getSelectOptionsList() {
		
		if( this.selectOptionsList == null ) {
			List<SelectItem> options = new ArrayList<SelectItem>();
			//normally I compute this by pulling in values from another source, iterated
			//these are statically added for demonstrative purposes
			options.add(new SelectItem( "value3", "label3" ));
			options.add(new SelectItem( "value1", "label1" ));
			options.add(new SelectItem( "value2", "label2" ));
			
			//auto-magic sorting! otherwise the order would be label3, label1, label2
			//results, based on the label, in label1, label2, label3
			Collections.sort( options, new LabelAscComparator() );
			
			selectOptionsList = options;
		}
		
		return selectOptionsList;
	}
	
	/**
	 * @param selectedOption String value being set via the EL binding;
	 * this is the data field for what has been selected, standard setter.
	 */
	public void setSelectedOption( String selectedOption ) {
		this.selectedOption = selectedOption;
	}
	
	/**
	 * Standard getter for the selectedOption property of the bean.
	 */
	public String getSelectedOption() {
		return this.selectedOption;
	}

}

SampleSelectItemBean.xsp.xml

<?xml version="1.0" encoding="UTF-8">
<xp:view>
	xmlns:xp="http://www.ibm.com/xsp/core">
	<xp:comboBox
		id="comboBox1"
		value="#{myBean.selectedOption}">
		<xp:selectItems>
			<xp:this.value><![CDATA[#{myBean.selectOptionsList}]]></xp:this.value>
		</xp:selectItems>
	</xp:comboBox>
</xp:view>