Spring Boot Setup and First App

Generate a project and run a first REST endpoint.

Spring Boot is the most widely used way to build Java backends. The Spring Framework provides dependency injection and a huge ecosystem; Spring Boot adds auto-configuration and sensible defaults so you can get a production-ready service running in minutes instead of days of XML and setup.

Generate a project

Go to start.spring.io, choose Maven or Gradle, Java 17 or newer, and add these dependencies: Spring Web, Validation, Spring Data JPA and H2 Database. Download, unzip and open it in your IDE.

cd demo
./mvnw spring-boot:run        # Windows: mvnw.cmd spring-boot:run

package com.example.demo;

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

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

@SpringBootApplication combines three things: configuration, component scanning (find your classes in this package and below) and auto-configuration. Because Spring Web is on the classpath, Boot automatically starts an embedded Tomcat server on port 8080. No separate server installation is needed.

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("/health")
    public java.util.Map<String, String> health() {
        return java.util.Map.of("status", "ok");
    }
}

curl 'http://localhost:8080/hello?name=Ada'
curl http://localhost:8080/health

Hello, Ada!
{"status":"ok"}

Returning a Map or an object is converted to JSON automatically by Jackson.

Project layout

• src/main/java: your code.
• src/main/resources/application.properties (or .yml): configuration such as the port.
• src/test/java: tests.
• pom.xml / build.gradle: dependencies and build.

@GetMapping("/time")
public String time() {
    return java.time.Instant.now().toString();
}
// application.properties:  server.port=9090