Step 2 — First Spring Boot 4 project

start.spring.io is the standard starting point.

Settings

• Project: Gradle - Kotlin DSL
• Language: Java
• Spring Boot: 4.0.x
• Java: 21
• Dependencies: Spring Web, Spring Data JPA, PostgreSQL Driver, Lombok, Validation

Generate → unzip → open in IntelliJ or VS Code.

First controller

@RestController
@RequestMapping("/api/hello")
public class HelloController {

    @GetMapping
    public String hello() { return "Hello, Spring!"; }

    @GetMapping("/{name}")
    public String greet(@PathVariable String name) { return "Hello, " + name + "!"; }
}

@RestController = JSON-response controller. @GetMapping = GET only.

Run

./gradlew bootRun

Default port 8080. Visit http://localhost:8080/api/hello.

Folder structure

demo/
├── build.gradle.kts
├── src/main/
│   ├── java/com/example/demo/
│   │   ├── DemoApplication.java   ← entry (@SpringBootApplication)
│   │   └── HelloController.java
│   └── resources/
│       ├── application.yml        ← DB URL, port
│       └── static/
└── src/test/

Try it

Add @PostMapping("/echo") that echoes the request body. Use @RequestBody Map<String, Object> for auto JSON parsing.

Next

Step 3 treats SQL as the single source of truth.