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.
Portlets in Action is the better book in my opinion, and while it refers heavily to Liferay in the examples it is still largely server agnostic. There is the chance it is a better Liferay reference book than Liferay in Action too