Chapter 1, Introduction to DSL and Groovy, discusses how DSLs can be used in place of general-purpose languages to represent different parts of a system. You will see how adding DSLs to your applications can open up the development process to other stakeholders in the development process. You'll also see how, in extreme cases, the stakeholders themselves can even become co-developers of the system by using DSLs that let them represent their domain expertise in code.

Chapter 2, Groovy Quick Start, covers a whistle-stop tour of the Groovy language. It also touches on most of the significant features of the language as a part of this tour.

Chapter 3, Groovy Closures, covers closures in some depth. It covers all of the important aspects of working with closures. You can explore the various ways to call a closure and the means of passing parameters. You will see how to pass closures as parameters to methods, and how this construct can allow us to add mini DSL syntax to our code.

Chapter 4, Example DSL: GeeTwitter, focuses on how we can start with an existing Java-based API and evolve it into a simple user-friendly DSL that can be used by almost anybody. You'll learn the importance of removing boilerplate code and how you can structure our DSL in such a way that the boilerplate is invisible to our DSL users.

Chapter 5, Power Groovy DSL Features, covers all of the important features of the Groovy language, and looks in depth at how some of these features can be applied to developing DSLs.

Chapter 6, Existing Groovy DSLs, discusses some existing Groovy DSLs that are in current use and are free to download.

Chapter 7, Building a Builder, explains how Groovy provides two useful support classes that make it much simpler to implement our own builders than if we use the MOP. You'll see how to use BuilderSupport and FactoryBuilderSupport to create our own builder classes.

Chapter 8, Implementing a Rules DSL, takes a look at Groovy bindings to see how they can be used in our DSL scripts. By placing closures strategically in the binding, you can emulate named blocks of code. You can also provide built-in methods and other shorthand by including closures and named Boolean values in the binding. These techniques can be used to a great effect to write DSL scripts that can be read and understood by stakeholders outside of the programming audience.

Chapter 9, Integrating it all, covers the many different ways in which you can integrate Groovy code into Java. You'll explore the issues around tightly integrating the two languages at compile time. You'll see how this can lead to dependency issues arising when Java code references Groovy classes and vice versa. You'll take a look at how you can use dependency injection frameworks like Spring to resolve some of these issues.

This book is for Java software developers who have an interest in building domain scripting into their Java applications. No knowledge of Groovy is required, though it will be helpful. The book will not teach Groovy, but will quickly introduce the basic ideas of Groovy. An experienced Java developer should have no problems with these and can move quickly onto the more evolved aspects of creating DSLs with Groovy.

No experience of creating a DSL is required. The book should also be useful for experienced Groovy developers who have so far only used Groovy DSLs such as Groovy builders and would like to start building their own Groovy-based DSLs.

In this book, you will find a number of styles of text that distinguish between different kinds of information. Here are some examples of these styles, and an explanation of their meaning.

Code words in text are shown as follows: "We can include other contexts through the use of the include directive."

A block of code is set as follows:

class Customer {
   int id
   String name
}

Any command-line input or output is written as follows:

$ groovyc monitor.groovy
$ java -cp $GROOVY_HOME/embeddable/groovy-all-1.6.6.jar:. monitor
HEAP USAGE
Memory usage : 1118880
Memory usage after GC: 607128

New terms and important words are shown in bold. Words that you see on the screen, in menus or dialog boxes for example, appear in the text like this: "clicking the Next button moves you to the next screen".

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