The author breaks the environment down into slices: Operating System, Application Server stack components, application code. Starting with the O/S, the book tells us the signs to watch for in various situations (i.e. how to detect and compensate for high or low utilization of the processor, or the disk.) The author explains likely causes for the problem, and what can be done about it.
Java programmers need to understand JVM tuning, and here it is given a whole chapter. This includes a lengthy explanation of how to correctly size your heap, followed by a nicely illustrated section on garbage collection, gc sizing, and choosing the best algorithm for your needs. All well done and very readable.
The book's subject is JBoss AS 5, and it's given a whole chapter, too. Thread pools and Connection pools are explained, as well as proper tuning of prepared statements and logging recommendations. Every programmer knows that logging can really drag performance down, right? Here we learn how to optimize it.
The middle of the book deals with JEE applications and the application server components that enable them. EJBs are given extensive coverage. JMS, a JEE hot-button, is also covered well. (Both JBoss Messaging and the newer HornetMQ are explained.)
The persistence layer is given holistic coverage. Starting with database design recommendations, the author proceeds to indexing, JDBC, connection pooling, and JPA/Hibernate. The Hibernate section is a good example of the kind of detail you'll find-- the author explains caching (first and second level) and the considerations you'll want to make to optimize their usage. Besides tuning the application server parts, there are recommendations for your application code, too. Hopefully you've bought into the recommendation to tune your code all throughout the development life cycle. If not, well, too bad for that one. Ditto for the database design.
One of the things JBoss makes really easy is clustering. Note: I didn't say cluster tuning, I said clustering. To optimize clustering, you'll have to understand all that low-level networky stuff like ethernet flow control and UDP buffer sizing. (I'm guessing this is not something your garden-variety developer thinks about every day, and make specific mention here as a demonstration of the kind of depth you get in this book.) Besides these bottom-layer concerns, the book also covers higher level parts of the stack like JGroups and JCache configuration, replication, and tuning cache storage. Unless you're really, really a bit-head, all that probably sounds a little deep. But the book explains it all in a way that makes it understandable and approachable.
JBoss uses Tomcat for it's web server tasks, so Tomcat is given good coverage as well. Nothing here seems JBoss specific, so most any Tomcat user could benefit from this part of the book. Connector configuration, thread pool sizing, and the Apache Portable Runtime are included. JBoss web server integration with Apache introduces us to mod_jk, mod_proxy, and mod_cluster. As throughout the book, the author uses JMeter to capture metrics to demonstrate to us the kind of performance we might get from each.
The final technical chapter deals with web application frameworks and web services. Web applications seem especially tunable in the development stage, while web services get code construction tips as well as configuration hints. The book ends with one more suggestion to make performance tuning part of your every day life rather than something crammed in after deployment time.
Like many technicians, I respect technical knowledge. This book is crammed full of it, and it's all presented in a readable manner. What's the bottom line? I'd recommend this book to any JBoss user (strongly), any JEE developer (with little reservation, especially Tomcat users), or any Java coder (who has a little extra money to spend.) Anyone else can probably live without this book. But if you're running JBoss (and you're technically minded), spend the money, you'll be glad you did.
The book can be found here: https://www.packtpub.com/jboss-as-5-performance-tuning/book