Spring Boot @Controller Annotation with Example

Spring Boot is a widely used framework for building robust and production-ready Java applications with minimal configuration. It simplifies web application development by combining powerful features such as Dependency Injection (DI), Aspect-Oriented Programming (AOP), and built-in support for RESTful web services.

In this article, we’ll explore the @Controller annotation in Spring Boot and understand its purpose, behavior, and usage through a practical example.

@Controller Annotation in Spring Boot

The @Controller annotation is a specialized form of the @Component annotation in the Spring Framework. It is used to mark a class as a Spring MVC Controller, responsible for handling web requests and returning responses.

Key Points:

• It is a part of the Spring MVC architecture.
• It is typically used with @RequestMapping to map HTTP requests to specific methods.
• It can only be applied at the class level.
• During component scanning, Spring automatically detects and registers classes annotated with @Controller.

Steps to Use the @Controller Annotation

Step 1: Create a Spring Boot Project

Create a new Spring Boot project using your preferred IDE (Eclipse, IntelliJ IDEA, or Spring Initializr).
If using Spring Initializr, select:

• Project: Maven
• Dependencies: Spring Web

Step 2: Add the spring-web dependency

In case your project does not include it by default, add the following dependency to your pom.xml:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

This provides the necessary libraries for creating web applications and REST APIs.

Step 3: Create a Controller Package

Create a package named controller under src/main/java/com/example/demo/. This package will contain the controller class that handles web requests.

Step 4: Create a Controller Class

Inside the controller package, create a file named DemoController.java.

package com.example.demo.controller;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

@Controller
public class DemoController {

    @RequestMapping("/hello")
    @ResponseBody
    public String helloGFG() {
        return "Hello GeeksForGeeks";
    }
}

• @Controller: Marks the class as a Spring MVC controller.
• @RequestMapping("/hello"): Maps the /hello URL to the helloGFG() method.
• @ResponseBody: Instructs Spring to return the method result directly as the HTTP response body, rather than looking for a view.

Step 5: Create the Main Application Class

Create a main class DemoApplication.java under the base package com.example.demo.

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 annotations:

• @Configuration: Marks the class as a source of bean definitions.
• @EnableAutoConfiguration: Enables automatic configuration based on classpath dependencies.
• @ComponentScan: Scans the package for annotated components like @Controller, @Service, and @Repository.

Step 6: Run the Application

Run the DemoApplication class as a Java Application. By default, the application starts on port 8080.

Access the endpoint at

http://localhost:8080/hello

If you want to change the port, modify the application.properties file:

server.port=8989

Output: