Spring Boot Hello World REST API Example

In this post, we will build a simple hello world REST API using Spring boot.

Spring Boot is an opinionated framework that helps developers build Spring-based applications quickly and easily. The main goal of Spring Boot is to quickly create Spring-based applications without requiring developers to write the same boilerplate configuration again and again.

Let's create a Spring boot application step by step.

1. Create Spring Boot Project

Spring Boot provides a web tool called https://start.spring.io to bootstrap an application quickly. Just go to https://start.spring.io and generate a new spring boot project.

Use the below details in the Spring boot creation:

Project Name: springboot-first-app

Project Type: Maven

Choose dependencies: Spring Web

Package name: com.springboot.app

2. Maven Dependencies

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<parent>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-parent</artifactId>
		<version>2.5.0</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.springboot.app</groupId>
	<artifactId>springboot-first-app</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>springboot-first-app</name>
	<description>Spring Boot First Application</description>
	<properties>
		<java.version>16</java.version>
	</properties>
	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-web</artifactId>
		</dependency>

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

	<build>
		<plugins>
			<plugin>
				<groupId>org.springframework.boot</groupId>
				<artifactId>spring-boot-maven-plugin</artifactId>
			</plugin>
		</plugins>
	</build>

</project>

3. Spring Boot Hello World REST API

Let's create a HelloWorldController class and the below code to it:

package com.springboot.first.app;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloWorldController {
	
	// GET HTTP Method
	// http://localhost:8080/hello-world
	@GetMapping("/hello-world")
	public String helloWorld() {
		return "Hello World!";
	}
}

• The above code uses Spring 4’s new @RestController annotation, which marks the class as a controller where every method returns a domain object instead of a view. It’s shorthand for @Controller and @ResponseBody rolled together.
• @GetMapping annotation for mapping HTTP GET requests onto specific handler methods. Specifically, @GetMapping is a composed annotation that acts as a shortcut for @RequestMapping(method = RequestMethod.GET).

4. Run Spring Boot Application

The below class SpringbootFirstAppApplication is the entry point that sets up the Spring Boot application. The @SpringBootApplication annotation enables auto-configuration and component scanning.

package com.springboot.first.app;

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

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

Run spring boot application from the IDE:

From your IDE, run the SpringbootFirstAppApplication.main() method as a standalone Java class that will start the embedded Tomcat server on port 8080 and point the browser to http://localhost:8080/.

Run spring boot application using the command line:

Just go to the root directory of the application and type the following command to run it -

$ mvn spring-boot:run

The application will start at Spring Boot’s default tomcat port 8080.

Just hit this link in a browser: http://localhost:8080/hello-world. You will able to see the response of this REST API in the browser.