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.
Try switching to JRE 6, which includes the javax.activation.DataSource interface, or use mr Dittmer's excellent tactic described below.
I can recommend http://jarfinder.com/ to help you find JAR files in which a given class/interface is located.