Book Image

Modular Programming in Java 9

By : Koushik Srinivas Kothagal
Book Image

Modular Programming in Java 9

By: Koushik Srinivas Kothagal

Overview of this book

The Java 9 module system is an important addition to the language that affects the way we design, write, and organize code and libraries in Java. It provides a new way to achieve maintainable code by the encapsulation of Java types, as well as a way to write better libraries that have clear interfaces. Effectively using the module system requires an understanding of how modules work and what the best practices of creating modules are. This book will give you step-by-step instructions to create new modules as well as migrate code from earlier versions of Java to the Java 9 module system. You'll be working on a fully modular sample application and add features to it as you learn about Java modules. You'll learn how to create module definitions, setup inter-module dependencies, and use the built-in modules from the modular JDK. You will also learn about module resolution and how to use jlink to generate custom runtime images. We will end our journey by taking a look at the road ahead. You will learn some powerful best practices that will help you as you start building modular applications. You will also learn how to upgrade an existing Java 8 codebase to Java 9, handle issues with libraries, and how to test Java 9 applications.
Table of Contents (19 chapters)
Title Page
Credits
About the Author
About the Reviewers
www.PacktPub.com
Customer Feedback
Preface

Understanding the migration goal


Let's assume you are done with the steps in the previous chapter and your legacy code now complies or runs in Java 9. You are ready for the next step--to migrate your code to use Java 9 modules! What does that look like?

Here's a very high-level picture that shows the different elements of a typical pre-Java 9 application running on a Java 9 platform:

You can break a typical application down into three distinct layers. At the very top layer are the application classes and jars. Typical applications have a combination of application classes and jars along with any internal libraries, such as shared utility components. All of these are application specific. Since the application is yet to be migrated to Java 9, this layer consists of classes and jars in the classpath.

The second layer denotes any frameworks that the application might be using. It's very rare to find Java applications these days that do not use an application framework of some sort. Frameworks...