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

Building libraries for multiple Java versions


When migrating applications, we had to deal with the scenario that the dependent libraries might not all be migrated to Java 9. When dealing with libraries, you'll need to tackle the opposite problem. The applications consuming your library may not all be Java 9. You'll have to support Java 8 (or perhaps even older versions of Java in some cases). How do you, as a library author, create library distributions for all those versions? Before Java 9, you used to have two options:

  • You could create separate JARs for each Java version
  • In your library code, you could use reflection to do a feature check. For example, you could reflectively access a platform API that was introduced in Java 8. If it works, you are in Java 8. If not, drop down to Java 7, and so on.

Both these options are tedious. There is a new alternative with Java 9, with a feature called multi-release JARs. The concept is simple. You create a special JAR file called a multi-release JAR...