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Creating Your First Java Module

In the previous chapter, we took a detailed look at the problems associated with modularizing Java code pre-Java 9, as well as the new module construct in Java 9 and Project Jigsaw. Before we examine how Java modularity solves these problems, you'll need to first understand what a Java module looks like. In this chapter, you'll create your first Java 9 module and learn what it takes to build and execute code in a Java module. Here are the top-level topics you'll be learning in this chapter:

Setting up the JDK with Java 9
Creating a new Java 9 module
Defining a module (using module-info.java)
Compiling and executing a module
Handling possible errors

You'll be building a sample Java 9 application throughout this book as you learn the different concepts related to modularity. The application you'll build is an address book...

Key benefits

Master design patterns and best practices to build truly modular applications in Java 9

Upgrade your old Java code to Java 9 with ease

Build and run a smooth functioning multi-module application.

Description

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.

Who is this book for?

This book is written for Java developers who are interested in learning and understanding the techniques and best practices to build modular applications in Java. The book assumes some previous programming experience in Java 8 or earlier, familiarity with the basic Java types such as classes and interfaces, as well as experience in compiling and executing Java programs.

What you will learn

• Get introduced to the concept of modules and modular programming by working on a fully modular Java application

• Build and configure your own Java 9 modules

• Work with multiple modules and establish inter-module dependencies

• Understand and use the principles of encapsulation, readability, and accessibility

• Use jlink to generate fully loaded custom runtime images like a pro

• Discover the best practices to help you write awesome modules that are a joy to use and maintain

• Upgrade your old Java code to use the new Java 9 module system

What do you get with Print?

Instant access to your digital eBook copy whilst your Print order is Shipped

Paperback book shipped to your preferred address

Download this book in EPUB and PDF formats

Access this title in our online reader with advanced features

DRM FREE - Read whenever, wherever and however you want

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Java_Guy Sep 27, 2017

This is one of the best book I came across recently. Author had really explained the topics well so as to understand the core concepts of Modular Programming in Java 9. I will certainly recommend this book to readers !!

Amazon Verified review

Mozart Brocchini Sep 07, 2017

Disclaimer: I was a technical reviewer of this book.The author gently introduces all concepts and then applies them with simple code examples or executing new commands on the terminal that were specifically added to Java 9 to help with modularity features.You will start by learning what problems the modularity features solve, then learn how to create your first module and progress incrementally all the way up to migrating existing code to java 9 and ultimately using modules with build tools and testing modules. You will also learn how the Java platform itself has been modularized and what benefits that brings. There is a new game changer feature that you shouldn't miss, the linking development phase which happens between compiling and executing code. Linking allows you to create self contained lightweight runtime images for your application with the usage of jlink tool rather then having to deploy the entire rt.jar like we did with previous versions of Java.I started reading this book with a lot of skepticism, my initial thinking was "Does modularity add any value to software development in today's world where modern architectures just expose APIs backed by microservice back ends ?". Well, it turns out that some of the new modularity features added to Java 9 like linking, actually help with creating more lightweight services.Fortunately, it turns out that this book will help Java 9 programmers with all the tasks related to modularity, including module design, best practices and patterns for modularizing new applications as well as retrofitting existing monoliths into modular systems which could later be broken into standalone microservices.I'm giving a four star rating based on topic coverage and accuracy, this book is excellent because it has everything you need to know about modularity with Java 9, you will find articles on web containing certain concepts but likely all articles will be incomplete and you will be only getting part of what Java 9 modules are about. While it is tempting to jump into learning the modularization features based on short tutorials, the modularity features are game changers and may only disappoint you if you start with a high level of frustration when failing to get things things done because of lack of knowledge. Just to give you and idea on how Java 9 is different, in Java 9 modular development, the classpath is no longer used to find dependencies.I obviously have not read all Java 9 books and never will, but my guess is that even Java 9 books that are not specifically targeting modularity will likely be short in modularity content.What could be improved:A few examples are based on older architectures and practices, those examples were chosen to exemplify some problems that modularity solve, but those issues no longer exist in more modern applications using microservices architecture and DevOps automation practices.Also, sometimes the topics feel a bit long for an experienced architect like me who wants to go right to the point.The verdict:If you are willing to learn Java modularity the right way, or have a complete reference focused exclusively on the new modularity features added in Java 9, this book is for you.

Modular Programming in Java 9: Build large scale applications using Java modularity and Project Jigsaw

What do you get with Print?

Modular Programming in Java 9

Creating Your First Java Module

Setting up the JDK

Switching between JDKs

Setting up the NetBeans IDE

Java 9 modules

Traditional Java code structure

Creating a module using NetBeans

The address book viewer application

Handling possible errors

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