The Spring @Controller and @RestController Annotations

Introduction

In the Spring Framework, @Controller and @RestController are two important annotations used for building web applications. These annotations are used to define classes that handle HTTP requests, but they have different purposes and behaviors. In this tutorial, we’ll explore these annotations, their differences, and provide examples of how to use them.

1. @Controller Annotation:

The @Controller annotation is used to mark a class as a Spring MVC controller. Controllers in Spring MVC are responsible for handling incoming HTTP requests, processing the requests, and returning an appropriate response. Typically, @Controller classes return a view name or a ModelAndView object, which represents the view and model data.

Example:

In this example, the MyController class is annotated with @Controller, and the hello() method is annotated with @GetMapping. When a GET request is made to the /hello endpoint, the hello() method is invoked, and it returns the view name “hello”. Spring MVC will then resolve this view name to an actual view and render it to the client.

2. @RestController Annotation:

The @RestController annotation is a specialized version of @Controller that is used to create RESTful web services. Unlike @Controller, which returns a view, @RestController returns the actual object that will be serialized into JSON or XML and sent back as an HTTP response. It is commonly used in combination with @RequestMapping, @GetMapping, @PostMapping, etc.

Example:

In this example, the MyRestController class is annotated with @RestController, and the hello() method is annotated with @GetMapping. When a GET request is made to the /api/hello endpoint, the hello() method is invoked, and it returns the string “Hello, World!”. Spring automatically converts this string into JSON and sends it back as an HTTP response.

Differences:

• @Controller is used for traditional web applications where views are rendered using server-side templates (e.g., JSP, Thymeleaf), while @RestController is used for building RESTful web services that return data in JSON or XML format.
• @Controller methods typically return view names or ModelAndView objects, while @RestController methods return the actual objects that will be serialized into the HTTP response body.

Conclusion:

In summary, the @Controller and @RestController annotations are fundamental components of the Spring MVC framework. @Controller is used for traditional web applications, while @RestController is used for building RESTful web services. Understanding when to use each annotation and their respective behaviors is essential for building effective and scalable Spring-based web applications.