Spring Boot - Hello World

Spring Boot is built on top of the Spring Framework and contains all the features of Spring. It has become a favorite of developers these days because of its rapid production-ready environment, which enables the developers to directly focus on the logic instead of struggling with the configuration and setup. Spring Boot is a microservice-based framework and making a production-ready application in it takes very little time. In this article, we will print "Hello World" using Spring Boot.

This article demonstrates two ways to print "Hello World" using Spring Boot:

1. Using the CommandLineRunner interface in Spring Boot
2. Using a Controller Class in Spring Boot

First, initialize the project on our machine. Spring Initializr is a web-based tool that we can use to easily generate the structure of the Spring Boot project. It also provides different features for the projects expressed in a metadata model. This model allows us to configure the list of dependencies that are supported by the JVM. Here, we will create the structure of an application using a spring initializer and then use an IDE to create a sample GET route. Therefore, to do this, the following steps are followed sequentially.

Step-by-Step Implementation

Step 1: Initialize the Spring Boot Project

We will use Spring Initializr to generate the Spring Boot project structure.

Go to Spring Initializr. Fill in the details as per the requirements.

Project: Maven
Language: Java
Spring Boot: 3.4.3 (or the latest stable version)
Packaging: JAR
Java: 17 (or later)
Dependencies: Spring Web

Here, we are using STS IDE

Provide the following details:

• Group: com.geeksforgeeks
• Artifact: SpringBootHelloWorld

Click on "Generate" to download the project as a ZIP file. Then Extract the ZIP file to a suitable location on your system.

Step 2: Import the Project in an IDE

After extract the zip file, now open STS IDE and then go to File > Import> Existing Maven Project > Next > Browse > Select the Project Folder > Finish.

After the project imports successfully, it will look like pictorially depicted as below:

Note: In the Import Project for Maven window, make sure you choose the same version of JDK which you selected while creating the project.

Method 1: Using CommandLineRunner Interface

In this method, we will use the CommandLineRunner interface to print "Hello world" when the application starts.

Step 3: Create the Main Application Class

• Go to src > main > java > com.geeksforgeeks.
• Open the SpringBootHelloWorldApplication.java file.

Replace its content with the following code:

package com.geeksforgeeks.SpringBootHelloWorld;

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

@SpringBootApplication

//Main class 
//Implementing CommandLineRunner interface 
public class SpringBootHelloWorldApplication 
 implements CommandLineRunner { 

 // Method 1 
 public void run(String args[]) throws Exception 
 { 
     // Print statement when method is called 
     System.out.println("HEllo world"); 
 } 
 
 // Method 2 
 // Main driver method 
 public static void main(String[] args) 
 { 
     // Calling run() method to execute 
     // SpringBootApplication by 
     // invoking run() inside main() method 
     SpringApplication.run( 
         SpringBootHelloWorldApplication.class, args); 
 } 

}

This application is now ready to run.

Step 4: Run the Spring Boot Application

Run the SpringBootHelloWorldApplication class and wait for the Tomcat server to start where the default port is already set.

Tip: The default port of the Tomcat server is 8080 and can be changed in the application.properties file.

Output: Generated on terminal/CMD 

Method 2: Using a Controller Class

In this method, we will create a controller class to handle incoming HTTP requests and return "Hello World" as a response.

Step 5: Create a Controller Class

Go to src > main > java > com.geeksforgeeks and create a new Java class named HelloWorldController.java. Below is the code for the controller.java file.

package com.geeksforgeeks.SpringBootHelloWorld.controller;

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

// Marking this class as a REST controller
@RestController
public class HelloWorldController { 

    // Mapping the root URL ("/") to this method
    @RequestMapping("/") 
    public String helloWorld() { 
        
        // Returning a simple "Hello World" response
        return "Hello World"; 
    } 
}

This controller helps to handle all the incoming requests from the client-side.

Step 6: Run the Application

• Run the Spring Boot application inside your IDE.
• Wait for the Tomcat server to start (Default port: 8080).

When the application runs successfully, it will show the the message that the application has started in the default port number 8080 as shown in following image:

Now we will use the PostMan and call the get API of the Spring boot application.

Visit http://localhost:8080/ in postman with GET request: