Spring Boot Project Setup

Spring Boot is an opinionated framework built on top of the Spring Framework that removes most of the manual configuration Spring traditionally required. Instead of wiring beans by hand and configuring an application server, you get a production-ready application by adding a handful of dependencies and letting Spring Boot's auto-configuration do the rest.

The fastest way to start a new project is Spring Initializr (start.spring.io), a web tool (also built into most IDEs) that generates a ready-to-run project skeleton. You choose the build tool (Maven or Gradle), the language (Java, Kotlin, or Groovy), the Spring Boot version, and the dependencies (starters) you need, and it produces a downloadable zip with the correct folder structure and build file already configured.

Standard Project Structure

A generated Spring Boot project follows a conventional Maven/Gradle layout that the framework expects by default.

• src/main/java — your application source code, rooted in a base package (e.g. com.webnest.app).
• src/main/resources — application.properties or application.yml, static assets, and templates.
• src/test/java — test classes, mirroring the main package structure.
• pom.xml (Maven) or build.gradle (Gradle) — declares the Spring Boot parent/plugin and dependencies.

The Main Application Class and @SpringBootApplication

Every Spring Boot app has exactly one entry-point class annotated with @SpringBootApplication, which is itself a convenience annotation combining three separate annotations: @Configuration (marks the class as a source of bean definitions), @EnableAutoConfiguration (triggers Spring Boot's auto-configuration mechanism), and @ComponentScan (scans the current package and sub-packages for components, controllers, services, and repositories). This is why placing your entry class at the root package matters — anything outside that package tree won't be scanned by default.

Running the Application

The main method calls SpringApplication.run(YourAppClass.class, args), which bootstraps the Spring ApplicationContext, starts the embedded server (Tomcat by default for web apps), and keeps the JVM alive to serve requests. You can run the app from your IDE, with mvn spring-boot:run, or as a standalone executable jar produced by mvn package.

Examples

package com.webnest.app;

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

@SpringBootApplication
public class WebnestAppApplication {

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

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _
( ( )\___ | '_ | '_| | '_ \/ _` |
 \\/  ___)| |_)| | | | | || (_| |
  '  |____| .__|_| |_|_| |_\__, |
 =========|_|==============|___/=

 :: Spring Boot ::                (v4.1.1)

... Tomcat started on port 8080 (http) with context path '/'
... Started WebnestAppApplication in 1.842 seconds

package com.webnest.app;

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

@SpringBootApplication
public class HelloWorldApplication {

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

    // A CommandLineRunner bean runs once, right after Spring Boot has started
    @Bean
    CommandLineRunner sayHello() {
        return args -> System.out.println("Hello, World from Spring Boot!");
    }
}

// Run it from the project folder:
//   Maven:  mvn spring-boot:run      (Windows: mvnw.cmd spring-boot:run)
//   Gradle: ./gradlew bootRun        (Windows: gradlew.bat bootRun)

 :: Spring Boot ::                (v4.1.1)

... Starting HelloWorldApplication using Java 21
... Started HelloWorldApplication in 0.912 seconds
Hello, World from Spring Boot!

<!-- pom.xml: add the web starter (named spring-boot-starter-web before Boot 4) -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-webmvc</artifactId>
</dependency>

// src/main/java/com/webnest/app/HelloController.java
package com.webnest.app;

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 + "!";
    }
}

Open http://localhost:8080/hello in a browser, or use curl:

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

curl "http://localhost:8080/hello?name=Webnest"
Hello, Webnest!

Exercise

Using the lesson's Minimal Spring Boot entry point generated by Initializr example, create a small implementation or design sketch that demonstrates Spring Initializr generates a ready-to-run project with the correct structure and build file for your chosen dependencies.. Add a test case or scenario that would catch Placing controllers or services in a package outside (or a sibling of) the package containing the @SpringBootApplication class — component scanning will silently skip them., and describe the expected result.

Quick quiz

Interview questions