Your First Spring Boot Application with Spring Initializr

Introduction

What is Spring Initializr?

The options on start.spring.io

• Project: the build tool - Maven, Gradle - Groovy or Gradle - Kotlin. This series uses Maven.
• Language: Java, Kotlin or Groovy. We use Java.
• Spring Boot: the Boot version. Initializr pre-selects the latest stable release, which at the time of writing is 4.1.2; versions marked SNAPSHOT or RC are previews and not meant for real projects.
• Project Metadata: Group com.javabrahman, Artifact first-app, a Description, and the Package name com.javabrahman.firstapp, which Initializr derives from the group and artifact.
• Packaging: Jar, the usual choice for Spring Boot, which runs with its own embedded web server. War is for deploying to an external server.
• Java: the Java version - 17, 21, 25 or 27 at the time of writing. Spring Boot 4 needs at least Java 17; this series uses Java 25, the current long-term-support release.
• Dependencies: the features the application needs. We add only Spring Web, for building web applications and REST APIs with Spring MVC.

curl https://start.spring.io/starter.zip -d type=maven-project -d bootVersion=4.1.2 -d javaVersion=25 -d groupId=com.javabrahman -d artifactId=first-app -d packageName=com.javabrahman.firstapp -d dependencies=web -o first-app.zip

The generated project

first-app
|-- .gitattributes
|-- .gitignore
|-- HELP.md                        links to the documentation of the chosen dependencies
|-- mvnw, mvnw.cmd                 the Maven wrapper scripts, for Unix and Windows
|-- .mvn/wrapper/                  wrapper settings: which Maven version to download
|-- pom.xml                        the Maven build file
`-- src
    |-- main
    |   |-- java/com/javabrahman/firstapp
    |   |   `-- FirstAppApplication.java     the main class
    |   `-- resources
    |       |-- application.properties       configuration
    |       |-- static/                      static web files (HTML, CSS, JavaScript)
    |       `-- templates/                   server-side templates, if a template engine is added
    `-- test/java/com/javabrahman/firstapp
        `-- FirstAppApplicationTests.java    a first test

The pom.xml

<?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>4.1.2</version>
		<relativePath/> <!-- lookup parent from repository -->
	</parent>
	<groupId>com.javabrahman</groupId>
	<artifactId>first-app</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<name>first-app</name>
	<description>My first Spring Boot application</description>
	<url/>
	<licenses>
		<license/>
	</licenses>
	<developers>
		<developer/>
	</developers>
	<scm>
		<connection/>
		<developerConnection/>
		<tag/>
		<url/>
	</scm>
	<properties>
		<java.version>25</java.version>
	</properties>
	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-webmvc</artifactId>
		</dependency>

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

Explanation of the pom.xml

• The parent, spring-boot-starter-parent version 4.1.2, gives the project Spring Boot's defaults: the versions of hundreds of libraries that are known to work together, compiler settings, resource filtering, and plugin configuration. That is why the dependencies below have no <version>.
• java.version 25 sets the Java version the code is compiled for.
• spring-boot-starter-webmvc is the starter for the Spring Web dependency. It brings Spring MVC, an embedded Tomcat server and JSON support in one dependency. (In Spring Boot 3 and earlier it was called spring-boot-starter-web; Spring Boot 4 renamed it.) Starters are covered in detail in Spring Boot Starters ExplainedClick to read tutorial: Spring Boot Starters Explained with Examples.
• spring-boot-starter-webmvc-test, with test scope, brings JUnit 5, AssertJ, Mockito and Spring's test support - used only for compiling and running tests, never packaged with the application.
• The spring-boot-maven-plugin adds the spring-boot:run goal and packages the application as an executable jar, covered in Packaging Spring Boot AppsClick to read tutorial: Packaging Spring Boot Apps: Executable and Layered JARs.
• The empty url, licenses, developers and scm elements are placeholders for project information; they can be filled in or deleted.

The main class

package com.javabrahman.firstapp;

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

@SpringBootApplication
public class FirstAppApplication {

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

}

Adding a REST controller

package com.javabrahman.firstapp;

import java.time.LocalDate;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {

	@GetMapping("/hello")
	public String hello(@RequestParam(defaultValue = "World") String name) {
		return "Hello, " + name + "!";
	}

	@GetMapping("/info")
	public AppInfo info() {
		return new AppInfo("first-app", "Spring Boot", LocalDate.of(2026, 11, 6));
	}

	public record AppInfo(String application, String builtWith, LocalDate date) {
	}

}

Explanation of the code

• @RestController makes the class a bean (component scanning finds it, since it is in the main class's package) and tells Spring MVC that its methods return response bodies rather than view names.
• @GetMapping("/hello") maps HTTP GET requests for /hello to the hello() method.
• @RequestParam(defaultValue = "World") binds the query parameter name, as in /hello?name=Nancy, falling back to World when it is absent.
• info() returns a recordClick to read: record. Spring Boot converts the returned object to JSON automatically, using the Jackson library that the web starter includes.

Running the application

./mvnw spring-boot:run

> curl http://localhost:8080/hello
Hello, World!

> curl http://localhost:8080/hello?name=Nancy
Hello, Nancy!

> curl http://localhost:8080/info
{"application":"first-app","builtWith":"Spring Boot","date":"2026-11-06"}

> curl http://localhost:8080/nothing-here
HTTP 404 {"timestamp":"2026-11-06T08:05:59.138Z","status":404,"error":"Not Found","path":"/nothing-here"}

Reading the startup log

2026-11-06T13:35:56.533+05:30  INFO 28648 --- [first-app] [           main] o.s.boot.tomcat.TomcatWebServer          : Tomcat initialized with port 8080 (http)
2026-11-06T13:35:56.611+05:30  INFO 28648 --- [first-app] [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2026-11-06T13:35:56.612+05:30  INFO 28648 --- [first-app] [           main] o.apache.catalina.core.StandardEngine    : Starting Servlet engine: [Apache Tomcat/11.0.27]
2026-11-06T13:35:56.816+05:30  INFO 28648 --- [first-app] [           main] b.w.c.s.WebApplicationContextInitializer : Root WebApplicationContext: initialization completed in 2948 ms
2026-11-06T13:35:58.180+05:30  INFO 28648 --- [first-app] [           main] o.s.boot.tomcat.TomcatWebServer          : Tomcat started on port 8080 (http) with context path '/'
2026-11-06T13:35:58.681+05:30  INFO 28648 --- [first-app] [nio-8080-exec-2] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring DispatcherServlet 'dispatcherServlet'
2026-11-06T13:35:58.682+05:30  INFO 28648 --- [first-app] [nio-8080-exec-2] o.s.web.servlet.DispatcherServlet        : Initializing Servlet 'dispatcherServlet'
2026-11-06T13:35:58.687+05:30  INFO 28648 --- [first-app] [nio-8080-exec-2] o.s.web.servlet.DispatcherServlet        : Completed initialization in 4 ms

Explanation of the log

• Each line shows the date and time, the level (INFO), the process id, the application name from spring.application.name, the thread, a shortened logger name, and the message. The format is explained in the tutorial on logging in Spring BootClick to read tutorial: Logging in Spring Boot: SLF4J, Logback and Log Levels.
• Tomcat initialized with port 8080: auto-configuration found Tomcat on the classpath and created an embedded server on the default port, 8080.
• Starting Servlet engine: [Apache Tomcat/11.0.27] shows the Tomcat version that Spring Boot 4.1.2 manages.
• Root WebApplicationContext: initialization completed: the application context, with all beans including our controller, is ready.
• Tomcat started on port 8080 (http) with context path '/': the server is accepting requests.
• The DispatcherServlet lines appeared only when the first request arrived, on a Tomcat request thread (nio-8080-exec-...): Spring MVC's front controller, which routes every request to a controller method, is initialized lazily.
• A normal startup also prints the Spring Boot banner, a Starting FirstAppApplication using Java ... with PID ... line, the active profiles, and a final Started FirstAppApplication in ... seconds line. They are switched off in this series' examples (with spring.main.banner-mode=off and spring.main.log-startup-info=false) because the startup line contains file paths of the machine the examples run on.

Running the generated test

package com.javabrahman.firstapp;

import org.junit.jupiter.api.Test;
import org.springframework.boot.test.context.SpringBootTest;

@SpringBootTest
class FirstAppApplicationTests {

	@Test
	void contextLoads() {
	}

}

[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 12.40 s -- in com.javabrahman.firstapp.FirstAppApplicationTests
[INFO] Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
[INFO] BUILD SUCCESS

Where to go from here

• Change the port: add server.port=9090 to application.properties - configuration is covered in application.properties vs application.ymlClick to read tutorial: application.properties vs application.yml in Spring Boot.
• Add dependencies later: open start.spring.io again, choose the same options plus the new dependency, and use Explore to see the resulting pom.xml; then copy the new <dependency> into your project.
• Restart automatically on code changes: add DevTools, covered in Spring Boot DevToolsClick to read tutorial: Spring Boot DevTools: Automatic Restart and Productivity.
• Ship it: ./mvnw package builds a jar you can run anywhere with java -jar.

Summary