// this is the Java code of the validator
package com.hp;

import javax.faces.application.FacesMessage;
import javax.faces.component.UIComponent;
import javax.faces.context.FacesContext;
import javax.faces.validator.Validator;
import javax.faces.validator.ValidatorException;

public class EmailValidator implements Validator {
	public void validate(FacesContext context, UIComponent component, Object value) throws ValidatorException {
		if (!value.toString().matches("[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?")) {
			FacesMessage message = new FacesMessage("Invalid E-Mail adress");
			// context.addMessage(component.getClientId(context), message);
			throw new ValidatorException(message);
		}
	}
}

<!-- this is the faces-config.xml entry -->
<validator>
	<validator-id>emailValidator</validator-id>
	<validator-class>com.hp.EmailValidator
	</validator-class>
</validator>

<!-- this is the implementation in the XPage -->
<xp:inputText value="#{comment.commentEmail}" id="commentEmail1" required="true" style="width:100%">
	<xp:this.validators>
		<xp:validateRequired message="Please provide your E-Mail">
		</xp:validateRequired>

		<xp:validator validatorId="emailValidator">
		</xp:validator>
	</xp:this.validators>
</xp:inputText>