"Java Performance and Scability Volume 1: Server-Side Programming Techniques" (Addison-Wesley; ISBN 0-201-70429-3) by Dov Bulka is one of those books that is made up on a series of tips (in this case, 48 of them). The book starts with an introduction.

Most of the rest of the book is a list of optimizations. Each one includes some explanation, some test code, and then some performance benchmark comparsions. Many of the suggestions are top notch. A few though are pretty shaky. In fact, the HotSpot team has said that some of the optimizations no longer work (e.g. Object Recycling).

This book's unique feature is that it covers associated technologies such as JNI, RMI, and Servlets. I'm aware of no other book that covers the performance issues of the latter two. The book concludes with an example of a writing a web server and optimizating to greatly improve performance.

In any case, the book is worth having because it does contain a lot of suggested optimizations that you can investigate when you are having performance problems.