Building RESTful Web Services with Spring Boot: A Beginner-Friendly Guide

Learn how to create RESTful Web Services with Spring Boot using this beginner-friendly guide. Includes step-by-step examples, best practices, and top interview questions for your preparation.

Imagine you and your friends are playing a game where everyone can request a candy from you. You’re in charge of handing out candies. Here’s how it works:

1. A friend asks, “Can I have one candy?”
2. You give them a candy if you have one, or you say, “Sorry, no candy left.”

In this example:

• You are the server (like a Spring Boot application).
• Your friends are the clients (like a browser or app).
• The candy requests are like HTTP requests.
• The candy is the data being shared.

RESTful Web Services work the same way—they enable servers (like your Spring Boot app) to share “candies” (data) with clients via HTTP.

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Step-by-Step Guide to Building RESTful Web Services in Spring Boot

1. What is REST?

REST (Representational State Transfer) is a set of principles for designing web services.
Key principles include:

• Statelessness: Each request from a client contains all the information needed to process it.
• Resources: Data is represented as resources identified by URIs (e.g., /api/users).
• HTTP Methods: Use HTTP verbs (GET, POST, PUT, DELETE) to interact with resources.

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2. Setting Up Spring Boot Project

Go to Spring Initializr and generate a project with the following dependencies:

• Spring Web
• Spring Boot DevTools
• Lombok

Unzip and import the project into your favorite IDE.

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3. Creating Your First RESTful Web Service

File: UserController.java

javaCopy codepackage com.example.demo.controller;

import org.springframework.web.bind.annotation.*;

import java.util.Arrays;
import java.util.List;

@RestController
@RequestMapping("/api/users")
public class UserController {

    @GetMapping
    public List<String> getUsers() {
        return Arrays.asList("Alice", "Bob", "Charlie");
    }

    @PostMapping
    public String addUser(@RequestBody String name) {
        return "User " + name + " added successfully!";
    }

    @DeleteMapping("/{name}")
    public String deleteUser(@PathVariable String name) {
        return "User " + name + " deleted successfully!";
    }
}

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4. Understanding the Code

1. @RestController: Marks this class as a REST API controller.
2. @RequestMapping("/api/users"): All endpoints in this controller will start with /api/users.
3. @GetMapping: Handles HTTP GET requests to fetch user data.
4. @PostMapping: Handles HTTP POST requests to add a new user.
5. @DeleteMapping("/{name}"): Handles HTTP DELETE requests to remove a user by their name.

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5. Testing the Endpoints

Use tools like Postman or cURL to test your RESTful API:

1. GET /api/users:
   Returns a list of users: ["Alice", "Bob", "Charlie"].
2. POST /api/users (Body: "David"):
   Response: "User David added successfully!".
3. DELETE /api/users/David:
   Response: "User David deleted successfully!".

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6. Best Practices for RESTful Web Services

1. Use Proper HTTP Status Codes: Return appropriate status codes like 200 OK, 201 Created, 400 Bad Request, 404 Not Found, etc.
2. Validate Input Data: Ensure the data received in requests is valid.
3. Handle Exceptions Gracefully: Use @ControllerAdvice to handle exceptions globally.
4. Enable CORS: To allow requests from different domains, configure CORS policies.

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7. Common Spring Boot RESTful Web Service Interview Questions

1. What is a RESTful Web Service?
   A RESTful Web Service is a service that adheres to REST principles and uses HTTP methods to expose data as resources.
2. What is the difference between @Controller and @RestController?
   • @Controller is used for MVC-based web applications and returns views.
   • @RestController is used for RESTful APIs and returns data directly as JSON or XML.
3. How do you handle exceptions in Spring Boot REST APIs?
   Use @ControllerAdvice along with custom exception handler methods annotated with @ExceptionHandler.
4. What are the HTTP methods supported in REST?
   • GET: Retrieve data.
   • POST: Create data.
   • PUT: Update data.
   • DELETE: Remove data.
5. How can you secure REST APIs in Spring Boot?
   • Use Spring Security for authentication and authorization.
   • Implement OAuth2 or JWT for token-based security.
6. What is the purpose of @RequestBody and @PathVariable?
   • @RequestBody: Maps the request payload to a method parameter.
   • @PathVariable: Extracts values from the URI path.