This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
To me,the advantage of ValidatorForm over ActionForm over seems to be -
In ActionForm you have to write all validation code in validate() but ValidatorForm the validation code which is common to many struts form can be put in a single class and mapped to different forms via validation.xml and validator-rules.xml files settings.