First, a quick word about OSGi. OSGi is a specification meant to make Java more "modular." In practice, this means it is an attempt to solve the age-old problem of "jar hell", including all the class loading issues that go with it. (Users of JEE application servers know what I'm talking about here.) OSGi lets you specify every external library your component needs, to the version. So if you need FooLib v1.2.3, and the application beside yours needs FooLib v10.9.8, that's not a problem at all-- both applications can happily run in the same OSGi container, at the same time.
Should you care about OSGi? The answer is maybe. It's without question a big deal to the makers of Java application containers-- everybody from JBoss to Mule has an opinion on OSGi, and many vendors are busy baking it into their infrastructure. What will differ to you, the user of the container, is how the container developers decided to make OSGi available to their users. This book is about how Spring went about it, and what you need to do to use Spring and OSGi together.
Spring DM (short for "Dynamic Modules") is a framework that enables you to use the popular Spring framework with OSGi. Spring, of course, comes with a multitude of components for solving all kinds of enterprise application needs. So this book is all about using Spring with OSGi.
It's a big book, over 500 pages, written by 3 authors. In those 500 pages you get lots of valuable content:
- An introduction to OSGi and an explanation of its purpose
- Explanation of how Spring can be used within an OSGi container, review of the currently available containers
- Details about how Spring DM works, and the parts you need to understand
- Details about OSGi services, and how they relate to Spring DM
- In depth best practices for data access, enterprise Java projects, and web applications (includes specific advice for popular web application frameworks)
- Testing practices
- Extended uses of OSGi, including likely future direction
A big part of what makes this book valuable are the many pieces of advice from the authors as they explain best practices for using various tools. So you want to use Eclipse, Ant or Maven? No problem, these are all covered. About to use MyFaces, Wicket, or DWR? All covered. Are you a Tomcat user or Jetty? Check and check. I'm sure you get the picture-- if you use these tools, the path ahead of you is already blazed and you can avoid some headaches by leveraging the author's experience.
Make no mistake about it, there will be some headaches ahead of you. Seldom is an application written today that doesn't use an external framework or library of some sort. Using these pre-packaged bits of functionality (and we need to be thankful for them!) might mean 're-packaging', if the library isn't offered as an OSGi bundle. This re-packaging means pealing apart some .jar files and editing the manifest files inside-- yuck! Luckily, this book offers you two things to help you with this task: tooling and advice. Tooling comes in handy because it can automate a lot of the manual, error-prone drudgery that goes along with such a task. Advice is even more valuable-- these authors have already worked done the hard work and have written down what you need to do to make your efforts successful.
So who is this book appropriate for? I'd say anyone who is going to use Spring DM. If you're convinced this is the right framework for your needs, you need a copy of this book. If you're not sure, or if you're just a casual reader wanting to know more about OSGi-- then I'd say you should look through the book first before you buy it. You might like it, or you might not because a lot of the book is all about hands-on use of Spring DM and the little tricks you need to make it work right the first time. But if you're just interested in an overview of the technology, this book might be too detail-oriented and not enough high-level for your tastes.
If you use Spring DM, you need to buy a copy of this book. It's going to be the definitive resource on the topic for a long time.
You can purchase Spring Dynamic Modules In Action from amazon.com. Slashdot welcomes readers' book reviews -- to see your own review here, read the book review guidelines, then visit the submission page.