Spring Boot @RequestBody Example

1. Introduction

The @RequestBody annotation in Spring Boot is used to bind the HTTP request body to a method parameter. It is particularly useful when you want to automatically deserialize incoming JSON or XML data into a Java object.

Key Points:

1. @RequestBody is essential for RESTful web services, where data sent by a client is bound to the request body.

2. The annotation tells Spring to use an HTTP message converter to convert the body of the request to a Java object.

3. It is typically used with POST and PUT HTTP methods where the request content is not form data but rather raw content like JSON or XML.

2. Implementation Steps

1. Define a Spring Boot application with the Web dependency.

2. Create a domain class that represents the data structure of the request body.

3. Define a controller class with a method that uses @RequestBody to deserialize the request body.

4. Use HTTP message converters to convert the request body to a Java object.

5. Run the application and test the endpoint with a tool like cURL, Postman, or any HTTP client.

3. Implementation Example

Here is the complete code that demonstrates the usage of @RequestBody annotation:

// Step 2: Define a domain class
class User {
    private String username;
    private String email;
    // Getters and Setters omitted for brevity
}

// Step 3: Create a controller with a method to handle the request body
@RestController
public class UserController {

    @PostMapping("/users")
    public ResponseEntity<String> createUser(@RequestBody User user) {
        // Step 4: Business logic to handle the user creation
        System.out.println("User Created: " + user.getUsername());
        return new ResponseEntity<>("User created successfully!", HttpStatus.CREATED);
    }
}

// Step 5: Main application class to run the Spring Boot application
@SpringBootApplication
public class RequestBodyExampleApplication {
    public static void main(String[] args) {
        SpringApplication.run(RequestBodyExampleApplication.class, args);
    }
}

Output:

User created successfully!

Explanation:

1. User is a simple Java class that represents the data structure for the request body.

2. @RestController marks UserController as a controller class, capable of handling web requests.

3. @PostMapping("/users") maps POST requests to /users to the createUser method.

4. @RequestBody User user tells Spring to deserialize the incoming request body into a User object.

5. Inside the createUser method, the user object would be processed, typically saving the user to a database.

6. RequestBodyExampleApplication is the main class that uses SpringApplication.run to launch the application.

7. When the /users endpoint is hit with a POST request, the createUser method is invoked, and it prints out a confirmation to the server's console and responds with a success message to the client.