Getting started with Spring Boot

This section will enable readers to get started with Spring Boot by explaining its features in detail. Furthermore, it will help you get started with Spring Boot application development by explaining the bare-bones of a Spring Boot application. Furthermore, it will explain the Spring Framework ecosystem and how it can be used in the Spring Boot application to harness the power of time-tested, industry-standard databases, messaging systems, and so on.

Learning about Spring Boot

Spring Boot is an application development framework for the Java virtual machine (JVM) that enables users to write stand-alone, production-grade, flexible, and extensible Spring-based applications with minimum code and configurations. This follows the Rapid application development (RAD) paradigm where the focus is on writing business logic that matters. With the introduction of cloud-based hosting services and microservice architectures, Spring Boot has been further elevated into a must-know technology platform. The following are some of its features:

• Standalone: A Spring Boot application is self-contained and easily deployable. It can start with its own embedded Tomcat, Jetty, Undertow web container, or as a console application from a just standard file such as Java Archive (JAR) or Web Archive (WAR). An example of this would be an application that has spring-boot-starter-web as a dependency, which when run will by default inside an embedded Tomcat web container.
• Production-grade: A Spring Boot application enables most of the features required for production, such as monitoring, connection pools, externalized configurations, and so on, out of the box, and ships with industry-standard, time-tested, and proven third-party applications such as Tomcat.

• Flexible: A Spring Boot application will have most of its settings auto-configured with default settings based on the dependencies available in the classpath of the application. But the auto-configuration will step back whenever a custom configuration is made. An example for this would be when a Spring Boot application finds a MySQL JDBC driver in the classpath; it auto-configures DataSource, which connects to the host localhost and port 3306, as those will be the settings for a MySQL Server with a default installation.
• Extensible: A Spring Boot application will have most core functionalities implemented out of the box, but also has a lot of Service Provider Interfaces (SPI), which are used by third-party developers to implement or modify functionality. An example of this would be when a requirement arises for a custom endpoint in Spring Boot Actuator; extending and overriding the AbstractEndpoint.invoke method in a Spring Bean will expose it as a new endpoint under Spring Boot Actuator.

Spring Boot does not do any code generation and does not require any XML files to be configured in order to run. Spring Boot is ideal for on-premise and cloud-based deployments with a quick boot-up time and a good memory footprint. The uniqueness of Spring Boot comes from its ecosystem of Spring modules, which covers security, data persistence, batch processing, and so on and from the highly active, competent community of developers who keep on improving the Spring Boot Framework.

Anatomy of a Spring Boot application

The anatomy of a Spring Boot application will be that it will be inheriting from a spring-boot-starter-parent project that will in return have all the common dependencies available for a Spring Boot application. Apart from this, there will be one or more spring-boot-starter POM such as spring-boot-starter-web, spring-boot-starter-jpa, and so on. The following example excerpt from pom.xml shows the basic dependencies of a Spring Boot application:

<parent>
   <groupId>org.springframework.boot</groupId>
   <artifactId>spring-boot-starter-parent</artifactId>
   <version>1.5.9.RELEASE</version>
   <relativePath/> <!-- lookup parent from repository -->
</parent>

<dependencies>
   <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter</artifactId>
   </dependency>
   ...
</dependencies>

The minimum bootstrapping point of a Spring Boot application will be a class with a main method that will be annotated with a @SpringBootApplication annotation along with the main method body, which calls the SpringApplication.run static method, for which a configuration class (a class with @Configuration annotation—the @SpringBootApplication annotation transitively has one) needs to be passed, along with a String array of arguments. The following code shows the minimum bootstrapping point of a Spring Boot application:

import org.springframework.boot.ApplicationRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;

@SpringBootApplication
public class SpringBootIntroApplication {

   public static void main(String[] args) {
      SpringApplication.run(SpringBootIntroApplication.class, args);
   }

   @Bean
   public ApplicationRunner applicationRunner() {
      return args -> {
         System.out.println("Hello, World!");
      };
   }
}

By running the preceding class, a Spring Boot application can be provisioned and executed. There are several ways to run a Spring Boot application; some of them are mentioned here:

• Running the Spring Boot application main class using an IDE.
• Building a JAR or WAR file using the following Maven command and then running:

$ mvn clean install
$ java -jar target/<package-name>.[jar|war]

• Run this using the Spring Boot Maven plugin:

$ mvn clean spring-boot:run

The @SpringBootApplication annotation comprises of @EnableAutoConfiguration and @ComponentScan annotations that do the heavy lifting of auto-configuring the Spring Boot application with the default settings and scanning the packages for any Spring-specific components such as services, components, repositories, and so on.

Supporting the Spring Framework ecosystem in Spring Boot

What made the Spring Boot application development framework stand out from other competing alternatives is the fact that it has a lot of supporting frameworks for easing development, with starter dependencies that cover industry-standard, enterprise-grade methodologies and tools such as Web MVC, JPA, MongoDB, Elasticsearch, Redis, and many more.

This makes Spring Boot a unique solution for day-to-day programming needs. By including a starter dependency, a Spring Boot application will have all the necessary dependencies and auto-configurations included in the application without any developer intervention.

This makes the life of a developer easy and enables us to focus on the business logic of the application instead of configurations and dependency management. At the time of writing, there are more than thirty of these starters available to be used in a Spring Boot application. The complete list can be found at https://github.com/spring-projects/spring-boot/tree/master/spring-boot-project/spring-boot-starters.

Spring Boot is a powerful framework as it has a very gradual learning curve and is built on the basis of the ability to write applications that just run with minimal effort. Having said that, Spring Boot should not be mistaken for a silver-bullet solution for all problems. In the areas of memory utilization, optimization, latency reduction, and many more, work may be needed, so developer commitment and effort are still required. But all in all, Spring Boot can be considered as a very good solution as it enables users to develop a minimum viable product (MVP) that is production-ready within maybe a couple of days or hours.