<validator type="requiredstring">
<param name="fieldName">username</param>
<message>username should not be null</message>
</validator>
<validator type="stringlength">
<param name="fieldName">username</param>
<param name="minLength">6</param>
<param name="maxLength">10</param>
<message>
username should be between ${minLength} and ${maxLength}
</message>
</validator>
</validators>