Creating a Spring Boot Project

Spring Boot builds on the Spring Framework with opinionated defaults: auto-configuration, embedded servers (Tomcat by default), starter dependencies and production features (Actuator). Generate a project at start.spring.io (Java 21, Maven or Gradle, plus the Web, Validation, Data JPA and Actuator dependencies), then run it with ./mvnw spring-boot:run or ./gradlew bootRun. The @SpringBootApplication class enables component scanning and auto-configuration for its package and sub-packages.

package com.example.shop;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

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

@RestController
class HelloController {
    @GetMapping("/hello")
    String hello() {
        return "Hello, Spring Boot";
    }
}

curl https://start.spring.io/starter.zip -d dependencies=web,validation,data-jpa,actuator,postgresql \
     -d javaVersion=21 -d type=maven-project -d groupId=com.example -d artifactId=shop -o shop.zip
./mvnw spring-boot:run        # http://localhost:8080/hello

Common pitfalls

• Placing classes outside the main class's package, so component scanning misses them.
• Adding many starters 'just in case' — each brings auto-configuration and startup cost.
• Using an unsupported Spring Boot version (check the support timeline).

Key points

• start.spring.io generates projects
• @SpringBootApplication = config + scanning + auto-config
• Embedded server, runnable JAR

Further reading: Spring Boot reference documentation