"While Tomcat is one of the most popular servlet containers, its inner workings still remain a mystery to many developers. If you only have a superficial familiarity of how this container actually functions, much of its power remains untapped and underutilized. [...]"
Before I start let me just mention that I’m experienced Java and Java EE developer and have worked with Tomcat server (with breaks) since version 4.x (year 2003). This means that I know how to develop, deploy, monitor and tune web applications in this web server. I also worked a little bit with Tomcat internals like custom class loaders. Despite that, this book gave me even more information and knowledge. With this book I was able not only to understand how Tomcat works internally but also where and how I could improve it or basically modify internal components for my needs.
Let’s start the review here - first of all I’d like to say that the author Damodar Chetty meets his goals in this book. He states in the preface that this book is not for web developers who want to learn how to write Java Servlet / JSP applications and how to deploy them in Tomcat container. I totally agree with the author – this book will not teach you that. This book is for people who want to know how Tomcat works internally in order to tune it or modify it for specific needs.
The author promises to go deep inside Tomcat’s architecture and implementation in order to better understand what’s under the hood, how it works and how you can improve or monitor it. I can assure you that this goal is met. This book describes in detail also other aspects of Java EE environment that are not directly connected to the Tomcat container but on which its implementation is based.
In this book Damodar Chetty firstly describes Tomcat’s high-level architecture and then breaks them down up to basic Java classes. This way he makes the whole complex architecture easy to understand. The author describes all Tomcat’s components one by one which is reflected in the Table of Contents. I think the author’s intention here was to make the reader read the book from cover to cover. I think so, because if you just want to learn about one particular component it will be a bit difficult to understand all the references to the previous sections. In my opinion this book should be read entirely to make every aspect clear, otherwise you will need to go back in the book and search for previously explained subjects, which is not easy.
This book is definitely component-oriented rather than how-to- or problem-oriented, so if you have a concrete problem or question regarding Tomcat you may have problems finding answer in this book.
All topics are difficult and in my opinion this book is for experienced Java and Java EE developers and administrators. In this field the book fully satisfied me. More so, many topics like "URLs and protocol handlers", "Java class loading" or "Implementing a custom class loader" may be very useful out of the scope of Tomcat server.
What I like in this book’s style is that all, even most complex subjects are explained in a clear way. Every complex component is broken down into pieces that are more easy to explain and understand. This book is also very concise in the source code examples. This makes it more time-consuming to read but on the other hand it forces the reader to understand the subject rather to copy-paste included source code. This aspect again makes this book accessible for experienced developers who know Java and Java EE environments pretty well and are able to start developing their own examples from the textual description.
This book does not promise to cover all the subjects around Tomcat but few of them are really missing in my opinion. Despite full description of how Tomcat is built and how it works I really miss chapters describing how to configure load-balancer for Tomcat or a cluster of Tomcat web servers. I know there are many books or Internet resources that cover these subjects but it would be just nice to have it here. I also realize that load-balancers and clustering components are not core Tomcat components and maybe this is the reason why they are not covered in this book.
To summarize, I think "Tomcat 6 Developer's Guide" book is a really good one and describes Tomcat web server in a pretty detailed fashion. Please note again that you will not learn from this book how to develop web applications using Java Servlet and JSP technologies. You will learn how to effectively use and also modify tomcat internals for you specific needs. You need to be experienced Java / Java EE developer to fully understand all the topics and successfully apply knowledge from this book. I would basically recommend you reading full description of this book available here before buying it.