Globus Toolkit 4 by Borja Sotomayor and Lisa Childers, ISBN-10: 0-12-369404-3 Morgan Kaufmann Publishers
There is an excellent book, Portlets and Apache Portals, by Stefan Hepper and others, by Manning Publications, which unfortunately was not published as a book, but is available for free download from http://www.manning.com I found the book to very good.