First controller

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Goal

Add a single @RestController that answers GET /hello with a plain string. After this page you will know how to wire one HTTP path to one Java method.

Prerequisites

• Create a Spring Boot project
• Methods

What a controller is

A controller in Spring is a class whose methods handle HTTP requests. You mark the class with @RestController and each method with a mapping annotation (@GetMapping, @PostMapping, and so on). The annotation tells Spring: when a request comes in for this path and method, call this Java method and send its return value back.

@RestController is short for "controller that returns the response body directly." The return value of each method is serialized straight to the response. For text it is sent as plain text; for objects it is sent as JSON (we will see that on the next page).

@GetMapping("/hello") binds the method to GET /hello. Use @PostMapping, @PutMapping, @DeleteMapping for the other verbs.

For the full set of mapping options, see the Spring MVC controller reference.

Code

In the project from the previous page, create a new file:

src/main/java/com/example/itemsapi/HelloController.java

package com.example.itemsapi;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {

    @GetMapping("/hello")
    public String hello() {
        return "hello from Spring Boot";
    }
}

Two things to notice:

• The package declaration matches the directory: com.example.itemsapi. Spring Boot's auto-scan only picks up classes under the package of the main @SpringBootApplication class. Putting HelloController in a different package would leave it invisible.
• No main method here. The main lives in ItemsApiApplication.java (Initializr generated it). Spring Boot starts the app from there, then finds your @RestController classes by scanning.

Run the app:

./mvnw spring-boot:run

In a second terminal:

curl http://localhost:8080/hello

Output:

hello from Spring Boot

Stop the server with Ctrl-C.

For frontend developers

@RestController plus @GetMapping("/hello") is the same pattern as an Express handler app.get('/hello', (req, res) => res.send('...')). The annotation is the registration; the method body is the handler.

Next → Returning JSON from a record list