Moving into Spring Boot

In the previous chapter, you learned how to set up your development environment for developing your REST APIs using Java and your Angular application. We also installed SDKMAN! to manage multiple versions of Java, a REST client to test APIs without the use of third-party tools, Angular DevTools to debug your Angular application, and Git for code versioning and collaboration.

This chapter will now teach you the concepts of Spring Boot. We will deep-dive into Spring Boot’s fundamentals and the essential things we need to learn to develop our backend application. We will also learn how to create a Spring Boot project using Spring Initializr.

In this chapter, we will cover the following topics:

• Understanding Spring Boot
• Using Spring Initializr
• Dependency injection
• Beans and annotations

Technical requirements

Here is what you need to complete this chapter:

• For building the backend: JetBrains’ IntelliJ IDEA and the Java 17 SDK
• For generating the Java project: Spring Initializr

Note

There will be no directories of repositories for chapters 1 to 4 because most topics here are only theory and feature some sample code. The actual application project will begin in w, Building APIs with Spring.

Understanding Spring Boot

We have already discussed an overview of Spring in Chapter 1, Spring Boot and Angular – The Big Picture. In this section, we will have a deeper understanding of the essential concepts of Spring Boot in building your backend application, but first, let’s recap what Spring Boot is and its significant advantages.

Spring Boot is an open source micro-framework from Pivotal. It is an enterprise-level framework for developers to create standalone applications on Java Virtual Machines (JVMs). Its primary focus is to shorten your code length to make it easier for you to run your application.

The framework extends the Spring Framework, which allows a more opinionated way to configure your applications. In addition, it comes with built-in autoconfiguration capabilities that configure both Spring Framework and third-party packages based on your settings.

Here are the significant advantages of Spring Boot:

• Auto-configuration: When configuring...

Using Spring Initializr

This section will explain what Spring Initializr is and how to configure and start our project. Spring Initializr is a web application that can generate a Spring Boot project on the fly. Spring Initializr will configure the build file with the required dependencies to run our project, focusing only on the code in the application. Spring Initializr makes it easier to set up our project, with the help of the Spring Boot CLI on the side, helping us configure our application. Spring Initializr generates a more traditional Java structure.

There are several ways to use Spring Initializr:

• Via a web-based interface
• Via Intellij IDEA

We will discuss these different ways to generate our Spring Boot application.

Web-based interface

The first way to use Spring Initializr is using a web-based interface. The application can be accessed through https://start.spring.io. You will see the following form once you open the link:

...

Dependency injection

We have successfully generated our own Spring Boot project, and now, we will start learning the concepts of Spring, and one of the most important concepts we need to understand is dependency injection. As we develop our backend using Spring Boot, we will mainly use dependency injection throughout our development, as this makes our Java program modular and enables easier switching of implementations.

Dependency injection is an essential feature of object-oriented programming languages, but first, let’s discuss the concept of inversion of control, which is what dependency injection is trying to achieve.

Inversion of control

Inversion of Control (IoC) is the design pattern used for object-oriented programming languages. IoC is the concept of inverting the flow of your program, and it is used for decoupling the components in your application, making your piece of code reusable and modular. Hence, the IoC design pattern will provide us with a way to...

Annotation and beans

Annotation and beans are essential parts of developing your Spring applications. They are considered the building blocks of Spring and make our code less boilerplate and maintainable.

Spring annotations are used to define the different types of beans. They are simply a form of metadata that marks our code to provide information. Conversely, beans are objects that are instantiated and created and can be injected with other beans. We will discuss more as we go through this section.

Types of annotations

Annotations in Spring are categorized into different types depending on their functionality. The following are annotations grouped into their respective categories.

Core annotations

Core annotations are used to leverage the Spring DI engine in our applications. They can be found in the org.springframework.beans.factory.annotation and org.springframework.context.annotation packages. The following is a list of core annotations:

• @Required: This...

Summary

With this, we have reached the end of this chapter. Let’s have a recap of the valuable things you have learned. You have learned the fundamentals of Spring Boot, its architecture, and the basics of REST. You have also learned how to use Spring Initializr to create your own Spring Boot project.

Dependency injection allows objects or classes to accept other dependencies that can implement different classes without writing them again. Annotations define the different types of beans; they are simply a form of metadata that marks our code to provide information.

And finally, beans are objects that form the backbone of an application managed by the Spring IoC container.

In the next chapter, we will be learning how to set up a database and use Spring Data JPA.