Spring Boot @Controller Annotation with Example

Spring Boot provides the @Controller annotation to define classes that handle web requests and control the flow of a web application. A controller acts as an intermediary between the user interface and the business layer, processing incoming requests and returning appropriate responses or views.

• Marks a class as a Spring MVC controller for handling HTTP requests.
• Maps URLs to specific handler methods using request mapping annotations.
• Interacts with service classes to process business logic.

Real-World Example

In an Employee Management System:

• A user opens /employees.
• The EmployeeController receives the request.
• The controller calls the service layer.
• The service fetches employee data from the repository.
• The controller sends the data to the view.
• The view displays the employee details to the user.

Steps to Use the @Controller Annotation

Follow these steps to create Controller in spring boot application.

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