Creating a Spring Boot Project and a First Endpoint

Spring Boot is the most widely used framework for building web APIs in Java. It builds on the Spring Framework and brings two essential things: auto-configuration (it guesses the configuration from the dependencies present) and an embedded web server (Tomcat by default). The result: an API starts with a simple main, with no server to install.

This course uses Spring Boot 4.1 (Spring Framework 7) with Java 25, the current LTS version of Java.

Generating the project

The official Spring Initializr site (start.spring.io), also built into IntelliJ IDEA and VS Code, generates the skeleton. It defaults to Gradle and Java 17: choose Maven, Java 25, a group (fr.boutique), and the Spring Web dependency. From the command line:

curl https://start.spring.io/starter.zip -d type=maven-project -d dependencies=web -d javaVersion=25 \
     -d groupId=fr.boutique -d artifactId=boutique -d packageName=fr.boutique -d baseDir=boutique -o boutique.zip
unzip boutique.zip

Resulting structure:

boutique/
├── pom.xml                       # dependencies (spring-boot-starter-webmvc...)
├── mvnw                          # Maven Wrapper: no need to install Maven
└── src/
    ├── main/java/fr/boutique/BoutiqueApplication.java
    ├── main/resources/application.properties
    └── test/java/fr/boutique/BoutiqueApplicationTests.java

Starters (spring-boot-starter-webmvc, -validation, -data-jpa…) group together consistent dependencies whose versions Spring Boot manages. The “Spring Web” dependency corresponds to the spring-boot-starter-webmvc starter (new name since Spring Boot 4); Spring Initializr also adds its test starter, spring-boot-starter-webmvc-test, because each module now has its own.

The main class

package fr.boutique;

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

@SpringBootApplication // auto-configuration + component scan of fr.boutique.*
public class BoutiqueApplication {
    public static void main(String[] args) {
        SpringApplication.run(BoutiqueApplication.class, args);
    }
}

Spring scans the package of this class and its subpackages: put your controllers in fr.boutique.produit, for example, never in a “sibling” package.

A first REST controller

package fr.boutique.produit;

import org.springframework.web.bind.annotation.*;
import java.util.List;

record ProduitDto(long id, String nom, double prix) {}

@RestController                 // returned values become the response body
@RequestMapping("/api")         // common prefix for the class's routes
class BonjourController {

    @GetMapping("/bonjour")     // GET /api/bonjour
    String bonjour() {
        return "Hello from Spring Boot";
    }

    @GetMapping("/produits")    // GET /api/produits
    List<ProduitDto> produits() {
        return List.of(new ProduitDto(1, "Clavier", 45.5),
                       new ProduitDto(2, "Écran", 180));
    }
}

@RestController combines @Controller and @ResponseBody. The Jackson library, included in the webmvc starter (Jackson 3 since Spring Boot 4, tools.jackson.* packages), automatically converts the record to JSON: [{"id":1,"nom":"Clavier","prix":45.5}, ...]. Records are perfect for this: immutable, concise, serialized with no configuration.

Running and testing

./mvnw spring-boot:run                 # starts on port 8080
curl http://localhost:8080/api/produits

To change the port, add to application.properties:

server.port=8081
spring.application.name=boutique

The startup logs show Tomcat started on port 8081. If the port is already in use, the application refuses to start: stop the old instance or change the port.

Key takeaways

• Spring Boot = Spring + auto-configuration + embedded server.
• A @RestController method annotated with @GetMapping becomes an endpoint.
• Returned objects are serialized to JSON by Jackson.