@RequestBody for JSON input in Spring Boot - Mini Project: Build & Apply

Using @RequestBody to Receive JSON Input in Spring Boot

📖 Scenario: You are building a simple Spring Boot web service that accepts user data in JSON format.This service will receive user details like name and age from a client application.

🎯 Goal: Create a Spring Boot controller that uses @RequestBody to accept JSON input and map it to a Java object.

📋 What You'll Learn

Create a Java class named User with fields name (String) and age (int).

Create a Spring Boot controller class named UserController.

Add a POST endpoint /users that accepts JSON input using @RequestBody mapped to User.

Return the received User object as the response.

💡 Why This Matters

🌍 Real World

APIs often receive data from clients in JSON format. Using @RequestBody in Spring Boot lets you easily convert that JSON into Java objects to work with.

💼 Career

Understanding how to accept and process JSON input is essential for backend developers working with REST APIs in Java and Spring Boot.

1

Create the User class

Create a Java class called User with two private fields: name of type String and age of type int. Add public getters and setters for both fields.

Spring Boot

// Your code here
// Create User class with private fields name and age, and public getters and setters

Need a hint?

Think of User as a box that holds name and age. You need methods to put values in and take values out.

2

Create the UserController class

Create a Spring Boot controller class named UserController annotated with @RestController. Import necessary Spring annotations.

Spring Boot

public class User {
    private String name;
    private int age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

// Your code here
// Create UserController class annotated with @RestController

Need a hint?

Use @RestController to tell Spring this class handles web requests and returns data directly.

3

Add POST endpoint with @RequestBody

Inside UserController, add a method createUser annotated with @PostMapping("/users"). This method should accept a parameter annotated with @RequestBody of type User and return the same User object.

Spring Boot

import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;

@RestController
public class UserController {
    // Your code here
    // Add createUser method with @PostMapping("/users") and @RequestBody User parameter
}

public class User {
    private String name;
    private int age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

Need a hint?

The @RequestBody annotation tells Spring to convert JSON from the request into a User object.

4

Complete the controller and test

Ensure the UserController class is complete with the createUser method returning the User object. This completes the setup to accept JSON input and respond with the same data.

Spring Boot

import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;

@RestController
public class UserController {
    @PostMapping("/users")
    public User createUser(@RequestBody User user) {
        // Your code here
    }
}

public class User {
    private String name;
    private int age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

Need a hint?

Returning the User object sends the same data back as JSON response.