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Modular Programming in Java 9

By : Kothagal

4.5 (2)

Modular Programming in Java 9

4.5 (2)

By: 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.

Preface

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Free Chapter

Introducing Java 9 Modularity

Introducing Java 9 Modularity

Modularity in Java

Rethinking Java development with packages

Java - the 20-year-old code base

Java Platform Module System

Project Jigsaw

Summary

Creating Your First Java Module

Creating Your First Java Module

Setting up the JDK

Switching between JDKs

Setting up the NetBeans IDE

Java 9 modules

Creating a module using NetBeans

The address book viewer application

Handling possible errors

Summary

Handling Inter-Module Dependencies

Handling Inter-Module Dependencies

Creating the second module

Compiling two modules

Configuring module dependency

Module versioning

Rethinking package structure

Understanding module path arguments

Revisiting classpath

Revisiting the classpath problems

Summary

Introducing the Modular JDK

Introducing the Modular JDK

Examining the legacy JDK

Enter Project Jigsaw

Platform modularity

Observable modules

Revisiting the two problems

Summary

Using Platform APIs

Using Platform APIs

Adding logging ability

Reading contacts from an XML file

Adding UI with Java FX

Summary

Module Resolution, Readability, and Accessibility

Module Resolution, Readability, and Accessibility

Readability

Accessibility

Tweaking modularity

Applying the concepts to address book viewer

Summary

Introducing Services

Introducing Services

The problem of coupling

Understanding services

Advanced services

Services and the module system goals

Summary

Understanding Linking and Using jlink

Understanding Linking and Using jlink

Module resolution process

Revisiting the state of the JDK

Linking using jlink

Building a modular JAR file

Summary

Module Design Patterns and Strategies

Module Design Patterns and Strategies

Designing modules

Modularizing by concerns

Modularizing by layers

Modularizing by change patterns

Designing API

Java modules coding patterns and strategies

Summary

Preparing Your Code for Java 9

Preparing Your Code for Java 9

Beginning Java 9 migration

Introducing the sample Java 8 application

Using the Java 9 compiler and runtime

Understanding the impact

Recommended strategy

Summary

Migrating Your Code to Java 9

Migrating Your Code to Java 9

Understanding the migration goal

Beginning the migration

Handling larger codebases

Migrating libraries

Building libraries for multiple Java versions

Summary

Using Build Tools and Testing Java Modules

Using Build Tools and Testing Java Modules

Integrating with Apache Maven

Unit testing modules with Java 9

Wrapping up

Summary

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Handling possible errors

Here are some possible errors you could run into when following the steps we previously outlined, along with some solutions:

Error during compilation:

      javac: invalid flag: --module-source-path

This is probably because you haven't switched to JDK 9 and are still using the Java 8 compiler. The --module-source-path option has been newly introduced to javac as of version 9.

Error during compilation:

      error: module not found: packt.addressbook

This error is because the Java compiler is unable to find the module-info.java file. Make sure it is in the right directory path.

Error during runtime:

      Error occurred during initialization of VM 
      java.lang.module.ResolutionException: Module packt.addressbook
      not found

This error indicates that the module file is not available in the module path provided. Make sure the path...

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