Objective

Understand RESTful web services and their implementation using Spring Boot. Learn to create, test, and consume REST APIs, including JSON-based CRUD operations, using Spring Boot’s REST support, Postman for testing, and RestTemplate for client-side invocation.

Lecture Topics

1. Introduction to Web Services

• Definition: Web services are standardized ways for applications to communicate over the internet, typically using HTTP.
• Types:
  • SOAP: XML-based, protocol-driven, with strict standards (e.g., WSDL).
  • REST: Representational State Transfer, lightweight, uses HTTP methods (GET, POST, PUT, DELETE) and typically JSON for data exchange.
• Key Characteristics of REST:
  • Stateless: Each request contains all necessary information; no server-side session.
  • Resource-Based: Operates on resources identified by URIs (e.g., /employees).
  • HTTP Methods: GET (read), POST (create), PUT (update), DELETE (delete).
  • JSON/XML: Commonly uses JSON for data representation.
• Benefits:
  • Scalability, flexibility, and interoperability.
  • Easy integration with web and mobile applications.

2. SOAP vs. RESTful Web Services

• SOAP:
  • Uses XML for messaging.
  • Requires WSDL for service description.
  • Strict standards, complex to implement.
  • Suitable for enterprise applications with high security needs (e.g., banking).
• REST:
  • Uses JSON or XML, simpler and lighter.
  • Leverages standard HTTP methods and status codes.
  • Easier to develop, test, and consume.
  • Ideal for web and mobile apps, microservices.
• Comparison:
  • SOAP: Heavyweight, rigid, secure (WS-Security).
  • REST: Lightweight, flexible, widely adopted for APIs.
• Exam Tip: Be able to compare SOAP and REST with examples of use cases.

3. RESTful Web Service Introduction

• Principles of REST (Roy Fielding’s constraints):
  • Client-Server: Separation of UI and data storage.
  • Stateless: No client state stored on the server.
  • Cacheable: Responses can be cached to improve performance.
  • Layered System: Clients cannot tell if they’re connected to the end server.
  • Uniform Interface: Standard methods (GET, POST, PUT, DELETE), resource URIs, and representations (JSON/XML).
• HTTP Status Codes:
  • 200 OK: Successful request.
  • 201 Created: Resource created (e.g., after POST).
  • 204 No Content: Successful but no content returned (e.g., after DELETE).
  • 400 Bad Request: Invalid request data.
  • 404 Not Found: Resource not found.
  • 500 Internal Server Error: Server-side error.
• REST in Spring:
  • Uses Spring MVC annotations (@RestController, @GetMapping, etc.).
  • Automatically converts Java objects to JSON using Jackson (included in spring-boot-starter-web).

4. Create RESTful Web Service in Java Using Spring Boot

• Key Annotations:
  • @RestController: Marks a class as a controller that returns JSON/XML (combines @Controller and @ResponseBody).
  • @RequestMapping: Maps HTTP requests to methods.
  • @GetMapping, @PostMapping, @PutMapping, @DeleteMapping: Maps specific HTTP methods.
  • @PathVariable: Extracts variables from the URI.
  • @RequestBody: Binds JSON payload to a Java object.