Parsing a Request Body in Spring Boot using @RequestBody Annotation

Spring Boot is a powerful framework that simplifies the process of building robust and scalable web applications.

In this article, we will explore how to parse a request body in Spring Boot using the @RequestBody annotation and Kotlin for our code examples.

let’s consider the following code snippet:

@RestController
@RequestMapping("/test")
class RestAPIController() {
    @PostMapping(value = ["/signup"], consumes = ["application/json"])
    fun signup(@RequestBody requestBody: User): ResponseEntity<String> {
      println("\nRequest Body: $requestBody")
      ResponseEntity.ok("SIGNED UP USER")
    }
}

The code above defines a Spring Boot REST API endpoint that handles a POST request to the “/signup” endpoint. The request body is expected to be in JSON format, and it will be parsed into a User object using the @RequestBody annotation.

The User class is not shown in the code snippet, but it should be a data class that contains properties matching the fields in the JSON request body.

For example, if the JSON request body looks like this:

{ 
  "firstname": "John", 
  "lastname": "Doe", 
  "mobileNumber": "+1234567890" 
}

Then the User class should look like this:

data class User(
  val firstname: String,
  val lastname: String,
  val mobileNumber: String
)

Notice that the property names in the User class must match the field names in the JSON request body.

Back to the code snippet, when a POST request is sent to the “/signup” endpoint, the Spring Boot framework will automatically parse the JSON request body into a User object and pass it to the signup() method as an argument. The @RequestBody annotation tells Spring Boot to do this.

Inside the signup() method, we can access the parsed User object through the requestBody parameter.

For example, we might store the User object in a database or send a confirmation email to the user.

Finally, we return a ResponseEntity object with a status code of 200 (OK) and a message indicating that the user has been signed up.

In summary, the @RequestBody annotation in Spring Boot is a powerful tool for parsing request bodies into objects. By using this annotation, we can simplify the process of receiving and processing user input data in web applications.