Introduction to Spring Boot

last modified July 31, 2023

This article is an introduction to the Spring Boot framework.

Spring

Spring is a popular Java application framework and Spring Boot is an evolution of Spring that helps create stand-alone, production-grade Spring based applications easily.

Spring Boot is a complete ecosystem for building enterprise applications. It includes many modules to build classic web, reactive applications, and microservices. Spring Boot applications can be developed in Java, Groovy or Kotlin.

The applications can be assembled in Maven or Groovy.

Spring Boot starters

Spring Boot applications are built using starters. Starters are a set of convenient dependency descriptors that you we include in our application. Starters are collections of all Spring and related technologies that helps us quickly set up our applications.

In other words, starters are convenient collections of dependecies. For instance, the spring-boot-starter-data-jdbc is a starter for using Spring Data JDBC.

dependencies { implementation ‘org.springframework.boot:spring-boot-starter-web’ implementation ‘org.springframework.boot:spring-boot-starter-data-jpa’ implementation ‘org.springframework.boot:spring-boot-starter-mustache’ runtimeOnly ‘mysql:mysql-connector-java’ }

The starters are added to the Maven and Gradle build files.

We can use Spring Initializr to initialize Spring Boot applications. It is availabe as an online service at https://start.spring.io/. It is also possible to use a Spring command line tool.

Spring Boot simple example

We create a simple Java web REST application.

build.gradle … src ├── main │ ├── java │ │ └── com │ │ └── zetcode │ │ ├── Application.java │ │ └── controller │ │ └── MyController.java │ └── resources │ ├── application.properties │ ├── static │ └── templates └── test

This is the project structure.

build.gradle

plugins { id ‘org.springframework.boot’ version ‘3.1.1’ id ‘io.spring.dependency-management’ version ‘1.1.0’ id ‘java’ }

group = ‘com.example’ version = ‘0.0.1-SNAPSHOT’ sourceCompatibility = ‘17’

repositories { mavenCentral() }

dependencies { implementation ‘org.springframework.boot:spring-boot-starter-web’ }

This is the Gradle build file. We include the spring-boot-starter-web starter which is used to create both classic ans REST web applications.

resources/application.properties

spring.main.banner-mode=off

In the application.properties file, we turn off the banner.

com/zetcode/controller/MyController.java

package com.zetcode.controller;

import org.springframework.http.ResponseEntity; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.PathVariable; import org.springframework.web.bind.annotation.RestController;

@RestController public class MyController {

@GetMapping(value="/status")
public ResponseEntity<String> status() {

    return ResponseEntity.ok("OK");
}

@GetMapping(value="/hello/{name}/")
public ResponseEntity<String> hello(@PathVariable String name) {

    var msg = String.format("Hello %s!", name);
    return ResponseEntity.ok(msg);
}

}

We have two endpoints: /status and /hello/{{name}}/.

@RestController public class MyController {

To create Restful applications, we use the @RestController annotation.

@GetMapping(value="/status") public ResponseEntity<String> status() {

return ResponseEntity.ok("OK");

}

We use ResponseEntity to build HTTP responses.

@GetMapping(value="/hello/{name}/") public ResponseEntity<String> hello(@PathVariable String name) {

var msg = String.format("Hello %s!", name);
return ResponseEntity.ok(msg);

}

We use the @PathVariable annotation to get the value from the path.

com/zetcode/Application.java

package com.zetcode;

import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication public class Application {

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

}

In the Application, we set up the application.

@SpringBootApplication public class Application {

With @SpringBootApplication, we initialize the Spring Boot application.

$ ./gradlew bootRun

We start the application.

$ curl localhost:8080/status -i HTTP/1.1 200 Content-Type: text/plain;charset=UTF-8 Content-Length: 2 Date: Mon, 31 Jul 2023 12:37:25 GMT

OK

$ curl localhost:8080/hello/Peter/
Hello Peter!

We generate requests to both endpoints with curl.

In this article we have introduced the Spring Boot framework.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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