This book initially appears excellent but on more detailed examination it proves to avoid the more difficult aspects.
The book assumes JBoss and a database server are both on the same machine. Initially the examples use the database server embedded in JBoss and then a separate MySQL server. Fine for learning but not for a real internet site where the two would contend for computer resources. The book singularly fails to address the configuration necessary to make JBoss function with a database installed on a separate machine.
The examples in the downloadable source code function correctly with the specified, now dated, version 4 of JBoss. Some, at least, cause errors with later versions.
However, making the examples work in a more complex "real world" situation will prove quite challenging and require reference to other sources of information and a lot of thought.