Java REST API Interview Questions and Answers for 5 years experience

1. What is REST?

   • Answer: REST, or Representational State Transfer, is an architectural style for designing networked applications. It uses a stateless, client-server, cacheable communications protocol, and a uniform interface. Key constraints include client-server, statelessness, cacheability, uniform interface, layered system, code on demand (optional).

2. Explain the difference between GET, POST, PUT, and DELETE HTTP methods.

   • Answer: GET retrieves data, POST creates new data, PUT updates existing data, and DELETE removes data. GET requests are typically idempotent (can be called multiple times without changing the result), while POST, PUT, and DELETE are not always idempotent. POST is often used for creating resources where the server assigns the ID, whereas PUT requires specifying the resource's ID.

3. What are HTTP status codes and give examples of a few important ones?

   • Answer: HTTP status codes indicate the outcome of a client's request. 200 OK signifies success, 400 Bad Request indicates an error in the client's request, 404 Not Found means the resource was not found, 500 Internal Server Error indicates a server-side problem.

4. What is HATEOAS and why is it important in RESTful API design?

   • Answer: HATEOAS (Hypermedia as the Engine of Application State) is a constraint of RESTful APIs where the response includes links to related resources, allowing the client to discover available actions and navigate the API without needing prior knowledge of its structure. It promotes decoupling and discoverability.

5. Explain the concept of RESTful API versioning.

   • Answer: API versioning is crucial for managing changes to the API over time without breaking existing clients. Common approaches include URI versioning (e.g., /v1/users), header versioning (using an Accept header), or content negotiation.

6. Describe different ways to handle exceptions in a REST API.

   • Answer: Exceptions should be handled gracefully and consistently, returning appropriate HTTP status codes and descriptive error messages in the response body (often in JSON or XML format). Custom exception handlers can centralize error processing.

7. What are some common Java frameworks used for building REST APIs?

   • Answer: Spring Boot, Jersey, RESTEasy, and Dropwizard are popular choices. Spring Boot is widely used due to its ease of use and comprehensive features.

8. Explain the use of annotations in Spring REST controllers.

   • Answer: Annotations like `@RestController`, `@RequestMapping`, `@GetMapping`, `@PostMapping`, `@PutMapping`, `@DeleteMapping`, `@PathVariable`, `@RequestParam`, and `@RequestBody` are used to map HTTP requests to controller methods and handle request parameters and data.

9. How do you handle authentication and authorization in a REST API?

   • Answer: Common approaches include OAuth 2.0, JWT (JSON Web Tokens), Basic Authentication, and API keys. The choice depends on security requirements and complexity. Spring Security provides robust support for authentication and authorization.

10. What is the difference between synchronous and asynchronous communication in REST APIs?

    • Answer: Synchronous communication involves the client waiting for a response from the server. Asynchronous communication allows the client to send a request and continue processing without waiting for an immediate response; the server might notify the client later (e.g., using websockets or callbacks).

11. Explain how to implement pagination in a REST API.

    • Answer: Pagination is used to handle large datasets by returning results in smaller chunks. This is typically achieved using query parameters like `limit` and `offset` or `page` and `size`. The response should include links to the next and previous pages.

12. What are some best practices for designing RESTful APIs?

    • Answer: Use consistent naming conventions, provide clear documentation, use appropriate HTTP methods, handle errors gracefully, design for scalability and maintainability, implement proper security measures, version your API.

13. Describe different ways to test a REST API.

    • Answer: Unit tests (testing individual components), integration tests (testing interactions between components), and end-to-end tests (testing the entire system) are common approaches. Tools like Postman, curl, and REST-assured are frequently used.

14. What is Swagger/OpenAPI and how does it help with API documentation?

    • Answer: Swagger/OpenAPI is a specification and set of tools for designing, building, documenting, and consuming RESTful web services. It allows for generating interactive API documentation from annotations or YAML/JSON definitions.

15. How do you handle data validation in a REST API?

    • Answer: Data validation is crucial. You can use frameworks like Hibernate Validator (in Spring) or manual validation using regular expressions or custom logic. Validation should happen on both the client and server sides.

16. Explain the concept of caching in REST APIs.

    • Answer: Caching improves performance by storing frequently accessed data closer to the client. HTTP caching mechanisms (e.g., using headers like `Cache-Control` and `Expires`) are commonly used, along with distributed caching solutions like Redis or Memcached.

17. How do you handle rate limiting in a REST API?

    • Answer: Rate limiting prevents abuse and ensures fairness. Techniques include token bucket algorithms, leaky bucket algorithms, and using API gateways with built-in rate limiting features.

18. Explain the importance of logging and monitoring in a REST API.

    • Answer: Logging provides valuable insights into API usage, errors, and performance. Monitoring tools can track key metrics (e.g., request latency, error rates, throughput) to identify issues and optimize performance. Tools like ELK stack, Prometheus, and Grafana are often used.

19. What are some security best practices for REST APIs?

    • Answer: Input validation, output encoding, secure authentication and authorization mechanisms, HTTPS, proper error handling (avoiding revealing sensitive information), regular security audits.

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