A working Java installation, JDK release. A Java 1.5+ should be good. I suggest using the Oracle Java 1.7, which is the current one at the time of writing this book.
The cURL tool, which will be used for most of the examples.
A working installation of Maven if you want to use the projects containing the code examples for customizations that are exposed in Chapter 9, Introducing Customizations. This is optional.
A Scala installation if you want to reproduce some of the scripts for downloading data from DBpedia. This is optional.