RestController annotation with example

The `@RestController` annotation in Spring Boot is a specialized version of the `@Controller` annotation. It combines `@Controller` and `@ResponseBody`, eliminating the need to annotate every request handling method with `@ResponseBody`.

When you use `@RestController`, Spring assumes that the methods in this class will return data (usually in the form of JSON or XML) directly to the client, rather than returning a view name to be resolved.

Example

Step 1: Create a Spring Boot Application

Ensure you have the necessary dependencies in your `pom.xml` (for Maven) or `build.gradle` (for Gradle).

Maven Dependency:
```xml
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>
```

Gradle Dependency:
```groovy
implementation 'org.springframework.boot:spring-boot-starter-web'
```

Step 2: Create the Main Application Class

Create the main class for the Spring Boot application.

```java
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);
    }
}
```

Explanation:

• @SpringBootApplication: Indicates a configuration class that declares one or more @Bean methods and also triggers auto-configuration and component scanning

Step 3: Create a REST Controller

Create a simple REST controller using the @RestController annotation.

```java
package com.example.demo.controller;

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

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

    @GetMapping("/hello")
    public String sayHello() {
        return "Hello, World!";
    }
}
```

Explanation:

• @RestController: Indicates that the class is a REST controller.
• @RequestMapping("/api"): Base URL for all endpoints in this controller.
• @GetMapping("/hello"): Maps HTTP GET requests to the sayHello method, which returns a string.

Step 4: Running the Application

Run the application from the main class (`DemoApplication`). When you navigate to `http://localhost:8080/api/hello` in your web browser, you should see the message: “Hello, World!”.

Conclusion RestController annotation

• @RestController: Combines `@Controller` and `@ResponseBody`, indicating that the class handles REST requests and the methods return data directly to the client.
• Example: Demonstrated how to use `@RestController` to create a simple REST API endpoint in a Spring Boot application.

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