How to Create your custom validator?
suppose that we want to create custome validator that applies some Arithmatic Operation on two fields.

1. Create the ComparisonValidator.2- Create the ComparisonValidatorTag. 3- Create the Validator.tld 4- Register the validator in the faces-config.xml 5- Now in the jsp page you can use it as following:

package com.aliabdelaziz;

/**
*
* @author aabdelaziz
*/
public class ComparisonValidator extends ValidatorBase
{
static Logger _logger = Logger.getLogger(ComparisonValidator.class);
/**
* Creates a new instance of FromThruValidator
*/
public ComparisonValidator() {
}
/**
*

The standard converter id for this converter.

*/
public static final String VALIDATOR_ID =
"com.aliabdelaziz.ComparisonValidator";

/**
*

The message identifier of the {@link FacesMessage} to be created if
* the equal_for check fails.

*/
public static final String EQUAL_MESSAGE_ID = "ArithmeticValidator";

//the foreign component_id on which the validation is based.
private String _for= null;
private String _operation= null;

// -------------------------------------------------------- ValidatorIF
public void validate(FacesContext facesContext, UIComponent uiComponent,
Object value) throws ValidatorException
{
_logger.info(" Now validating... validate(FacesContext facesContext,
UIComponent uiComponent, Object value) ");

if (facesContext == null) throw new NullPointerException("facesContext");
if (uiComponent == null) throw new NullPointerException("uiComponent");
if (value == null)
{
return;
}

UIComponent foreignComp = uiComponent.getParent().findComponent(_for);
if(foreignComp==null)
throw new FacesException("Unable to find component '" + _for + "' (calling
findComponent on component '" + uiComponent.getId() + "')");

if(false == foreignComp instanceof EditableValueHolder)
throw new FacesException("Component '" + foreignComp.getId() + "' does not
implement EditableValueHolder");

EditableValueHolder foreignEditableValueHolder =
(EditableValueHolder) foreignComp;

if (foreignEditableValueHolder.isRequired() &&
foreignEditableValueHolder.getValue()== null )
{
return;
}

Object[] args = {value.toString(),(foreignEditableValueHolder.getValue()==null) ? foreignComp.getId():foreignEditableValueHolder.getValue().toString()};

if(_operation.equals("greaterThan"))
{
//do the comparison for greaterThan here
}
else if(_operation.equals("lessThan"))
{
//do the comparison for lessThan here
}
else if(_operation.equals("equal"))
{
//do the comparison for equal here
}
else
{
// means this is un known charactar.
FacesMessage message = new FacesMessage();
_logger.info("******> Message = " +
Messages.getMessageString("ComparisonValidator"));

message.setDetail(Messages.getMessageString("ComparisonValidator"));

message.setSummary(Messages.getMessageString("ComparisonValidator"));
message.setSeverity(FacesMessage.SEVERITY_ERROR);
throw new ValidatorException(message);
}
}
// -------------------------------------------------------- StateholderIF

public Object saveState(FacesContext context)
{
Object values[] = new Object[6];
values[0] = super.saveState(context);
values[1] = _for;
values[1] = _operation;
return values;
}

public void restoreState(FacesContext context, Object state)
{
Object values[] = (Object[])state;
super.restoreState(context, values[0]);
_for = (String)values[1];
_operation = (String)values[2];
}
// -------------------------------------------------------- GETTER & SETTER

/**
* @return the foreign component_id, on which a value should be validated
*/
public String getFor()
{
return _for;
}

/**
* @param string the foreign component_id, on which a value should be validated
*/
public void setFor(String string) {
_for = string;
}

/**
* @return the Comparison operation name.
*/
public String getOperation()
{
return _operation;
}

/**
* @param string the Comparison operation
*/
public void setFor(String string) {
_operation = string;
}
}

/**
*
* @author aabdelaziz
*/
public class ComparisonValidatorTag extends ValidatorBaseTag {

/**
* Creates a new instance of ComparisonValidatorTag
*/
public ComparisonValidatorTag() {
}

private static final long serialVersionUID = -3249115551944863108L;
//the foreign component_id on which the validation is based.
private String _for = null;

public void setFor(String string) {
_for = string;
}

private String _operation = null;

public void setOperation(String string) {
_operation = string;
}

protected Validator createValidator() throws JspException
{
FacesContext facesContext = FacesContext.getCurrentInstance();
setValidatorId(ComparisonValidator.VALIDATOR_ID);
ComparisonValidator validator = (ComparisonValidator)super.createValidator();
if (_for != null)
{
if (UIComponentTag.isValueReference(_for))
{
ValueBinding vb = facesContext.getApplication().createValueBinding(_for);
validator.setFor(new String(vb.getValue(facesContext).toString()));
}
else
{
validator.setFor(_for);
}
}

if (_operation != null)
{
if (UIComponentTag.isValueReference(_operation)))
{
ValueBinding vb = facesContext.getApplication().createValueBinding(_operation);
validator.setMethodName(new String(vb.getValue(facesContext).toString()));
}
else
{
validator.setMethodName(_operation);
}
}

return validator;
}

public void release() {
super.release();
_for = null;
_operation = null;
}
}

<taglib version="2.0" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee web-jsptaglibrary_2_0.xsd">
<tlib-version>1.0</tlib-version>
<short-name>cv</short-name>
<uri>/WEB-INF/validators</uri>
<description>
MyFaces subproject that contains components and other goodies to be used with any JSF implementation.
</description>

<tag>
<name>validateComparison</name>
<tag-class>com.aliabdelaziz.ComparisonValidatorTag</tag-class>
<body-content>JSP</body-content>
<description>
A custom validator for validations against foreign component values.

Unless otherwise specified, all attributes accept static values or EL expressions.
</description>
<!--
This attribute indicates an alternate validation error message format string to display.
-->
<attribute>
<name>message</name>
<required>false</required>
<rtexprvalue>false</rtexprvalue>
<description>
alternate validation error message format string
</description>
</attribute>

<name>for</name>
<required>true</required>
<rtexprvalue>false</rtexprvalue>
<description>
the id of the foreign component, which is needed for the validation
</description>
</attribute>
<attribute>
<name>operation</name>
<required>true</required>
<rtexprvalue>false</rtexprvalue>
<description>
the id of the foreign component, which is needed for the validation
</description>
</attribute>
</tag>
</taglib>

<validator>
<validator-id>com.oc.itworx.HR.validators.employmentFromDateValidator</validator-id>
<validator-class>com.oc.itworx.HR.validators.EmploymentFromDateValidator
</validator>

<%@ taglib uri="/WEB-INF/validators" prefix="cv"%>

<h:inputText maxlength="7" id="Input_1" value="#{managedBean.input1}" required="true" />

<h:inputText maxlength="7" id="Input_2" value="#{managedBean.input2}" required="true" >

<cv:validateRangesOverlapping for="Input_1" methodName="lessThan"/>

</h:inputText>