Java is a huge subject, so I've organzized this section into:
In addition to my architectural design recommendations, here are some suggested texts for developers:
Thinking
in Java (4th Edition)
by Bruce Eckel.
Bruce Eckel is an excellent author and a pioneer of online feedback: visit his site.
Java developers wanting to take their skill even further will want to read and digest ever issue of the Java Specialists Newsletter. Many of the topics explain things you could do, but probably shouldn't. Still, it's very helpful to know how and why not to do something.