@Controller vs. @RestController Annotation in Spring

Spring Framework provides two commonly used annotations for handling web requests: @Controller and @RestController. They may look similar, but they are designed for different purposes:

• @Controller is typically used for MVC-based web applications (returning HTML views).
• @RestController is used for RESTful APIs (returning JSON/XML responses)

@Controller Annotation

• @Controller is a Spring annotation used to define a web controller in an MVC (Model-View-Controller) application.
• It usually works with view resolvers (like Thymeleaf, JSP or FreeMarker) to return HTML pages.
• If you want to return JSON/XML data, you must use @ResponseBody with each method.

Example: Using @Controller in a Spring MVC Application

@Controller
public class HomeController {
    
    @GetMapping("/home")
    public String homePage(Model model) {
        model.addAttribute("message", "Welcome to Spring MVC!");
        
        // Returns a view (home.html or home.jsp)
        return "home"; 
    }
}

Explanation:

• The @Controller annotation marks the class as a Spring MVC controller.
• The homePage() method maps to /home and returns a view named home.

@RestController Annotation

• The @RestController annotation is used for making restful web services.
• This annotation is used at the class level and allows the class to handle the requests made by the client.
• The RestController allows to handle all REST APIs such as GET, POST, Delete and PUT requests. 
• It is equivalent to-> @Controller + @ResponseBody

Example: Using @RestController in a REST API

@RestController
public class ProductController {
    
    @GetMapping("/product")
    public Product getProduct() {
        return new Product(1, "Laptop", 80000);
    }
}

Explanation:

• The @RestController annotation combines @Controller and @ResponseBody.
• The getProduct() method returns a Product object that is automatically converted into JSON.

@Controller vs @RestController

The table below demonstrates the differences between @Controller and @RestController annotations in Spring.

When to Use Which

Use @Controller when:

• You are building a web application that returns HTML pages.
• You want to integrate with frontend template engines like Thymeleaf or JSP.

Use @RestController when:

• You are building REST APIs for mobile apps, SPAs or microservices.
• You need to exchange data in JSON/XML format.