What libraries are available that support credit card validation from Java?

See Roedy Green's Credit Card Validation Amanunensis

The cmp.CreditCard.CreditCardValidate class will help you tell if a credit card number is valid. It will also tell you which of the following credit card companies issued the card: Amex, Diners Club, Carte Blanche, Discover, enRoute, JCB, MasterCard or Visa.

It validates the prefix and the checkdigit. It does not contact the credit card company to ensure that number has actually been issued and that the account is in good standing.