Book Image

Java 9 Dependency Injection

By : Nilang Patel, Krunal Patel
3 (1)
Book Image

Java 9 Dependency Injection

3 (1)
By: Nilang Patel, Krunal Patel

Overview of this book

Dependency Injection (DI) is a design pattern that allows us to remove the hard-coded dependencies and make our application loosely coupled, extendable, and maintainable. We can implement DI to move the dependency resolution from compile-time to runtime. This book will be your one stop guide to write loosely coupled code using the latest features of Java 9 with frameworks such as Spring 5 and Google Guice. We begin by explaining what DI is and teaching you about IoC containers. Then you’ll learn about object compositions and their role in DI. You’ll find out how to build a modular application and learn how to use DI to focus your efforts on the business logic unique to your application and let the framework handle the infrastructure work to put it all together. Moving on, you’ll gain knowledge of Java 9’s new features and modular framework and how DI works in Java 9. Next, we’ll explore Spring and Guice, the popular frameworks for DI. You’ll see how to define injection keys and configure them at the framework-specific level. After that, you’ll find out about the different types of scopes available in both popular frameworks. You’ll see how to manage dependency of cross-cutting concerns while writing applications through aspect-oriented programming. Towards the end, you’ll learn to integrate any third-party library in your DI-enabled application and explore common pitfalls and recommendations to build a solid application with the help of best practices, patterns, and anti-patterns in DI.
Table of Contents (14 chapters)
Title Page
Copyright and Credits
Packt Upsell
Contributors
Preface
Index

Annotation-based DI


From the beginning, the most common way of defining configuration in Spring has been XML-based. But when the complexity grew and navigation of beans became exhausted in the jungle of angle brackets, there was a demand for a second option to define configuration. As a result, Spring started support for annotation.

Annotation-based configuration is an alternate of XML-based configuration, and it relies on bytecode metadata. Spring started support for annotation with version 2.5. With annotation, the configuration moves from an XML to component class. Annotation can be declared on classes, methods, or at field level.

Let's understand the process of defining configuration through annotation. We will first understand this process through XML configuration, and then will gradually move to annotation-based configuration in the following sections.

DI through XML configuration

It's always good to start with the most common option. So first, we will take an example of pure XML-based...