Spring Boot Interview Questions

The @RestController and @RequestMapping annotations in Spring Boot are used to build RESTful web services. They simplify the process of mapping HTTP requests to handler methods in your controller classes.

@RestController

• Purpose: The @RestController annotation is a specialized version of the @Controller annotation. It is used to create RESTful web services by combining @Controller and @ResponseBody.
• Functionality:
  • Marks the class as a controller where every method returns a domain object instead of a view.
  • All methods in a class annotated with @RestController will have their return values serialized into the HTTP response body.
• Example:

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

@RestController
public class MyRestController {

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

In this example, the sayHello method returns a string that will be written directly to the HTTP response body.

@RequestMapping

• Purpose: The @RequestMapping annotation is used to map HTTP requests to handler methods of MVC and REST controllers.
• Functionality:
  • Can be applied at the class level and method level.
  • Defines the URL patterns and HTTP methods that a particular handler method or class should process.
• Attributes:
  • value or path: The URL pattern to which the handler method is mapped.
  • method: The HTTP method (GET, POST, PUT, DELETE, etc.) that the handler method should support.
  • params, headers, consumes, produces, etc.: Additional constraints for the mapping.
• Example:

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

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

    @RequestMapping(value = "/greet", method = RequestMethod.GET)
    public String greet() {
        return "Greetings from the API!";
    }
}

In this example, the greet method is mapped to handle GET requests to /api/greet.

Simplified Annotations for Specific HTTP Methods

Spring Boot also provides shortcut annotations for common HTTP methods, which are more concise than using @RequestMapping with the method attribute.

• @GetMapping: Shortcut for @RequestMapping(method = RequestMethod.GET)
• @PostMapping: Shortcut for @RequestMapping(method = RequestMethod.POST)
• @PutMapping: Shortcut for @RequestMapping(method = RequestMethod.PUT)
• @DeleteMapping: Shortcut for @RequestMapping(method = RequestMethod.DELETE)

Example Using Shortcut Annotations

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.PutMapping;
import org.springframework.web.bind.annotation.DeleteMapping;
import org.springframework.web.bind.annotation.RestController;

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

    @GetMapping("/greet")
    public String greet() {
        return "Greetings from the API!";
    }

    @PostMapping("/create")
    public String create() {
        return "Create a new resource";
    }

    @PutMapping("/update")
    public String update() {
        return "Update an existing resource";
    }

    @DeleteMapping("/delete")
    public String delete() {
        return "Delete a resource";
    }
}

Combining @RestController and @RequestMapping

You can combine @RestController with @RequestMapping at the class level to apply a common base path to all methods within the controller.

Example

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

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

    @GetMapping("/greet")
    public String greet() {
        return "Greetings from the API!";
    }

    @PostMapping("/create")
    public String create() {
        return "Create a new resource";
    }
}

In this example, the base URL /api is applied to all methods in the MyApiController class, making the endpoints /api/greet and /api/create.

Summary

• @RestController:
  • Combines @Controller and @ResponseBody.
  • Marks the class as a RESTful controller where every method returns data directly written to the HTTP response body.
• @RequestMapping:
  • Maps HTTP requests to handler methods.
  • Can define URL patterns, HTTP methods, and other request constraints.
  • Can be used at both class and method levels.
• Shortcut Annotations:
  • @GetMapping, @PostMapping, @PutMapping, @DeleteMapping provide more concise ways to map specific HTTP methods.

Using @RestController and @RequestMapping (or its shortcuts) effectively allows you to build powerful and efficient RESTful web services in Spring Boot.