Java REST API Interview Questions and Answers for 10 years experience

1. What is a REST API?

   • Answer: A RESTful API (Representational State Transfer Application Programming Interface) is a software architectural style for building web services. It uses HTTP methods (GET, POST, PUT, DELETE) to interact with resources, identified by URIs, and relies on stateless communication, meaning each request contains all the information needed to process it.

2. Explain different HTTP methods used in REST APIs.

   • Answer: GET (retrieves data), POST (creates data), PUT (updates data), DELETE (deletes data), PATCH (partially updates data), HEAD (retrieves headers only), OPTIONS (describes communication options).

3. What are RESTful constraints?

   • Answer: Client-server, Stateless, Cacheable, Uniform interface (using standard methods and representations), Layered system, Code on demand (optional).

4. Explain the concept of statelessness in REST.

   • Answer: Each request from a client to the server must contain all the information necessary to understand and process the request. The server doesn't store any context about the client between requests.

5. What is HATEOAS?

   • Answer: HATEOAS (Hypermedia as the Engine of Application State) is a REST architectural constraint. It means that the responses from the API should include links to related resources, allowing the client to discover available actions without prior knowledge of the API structure.

6. What are different status codes in HTTP responses and their meanings?

   • Answer: 2xx (Success), 3xx (Redirection), 4xx (Client Error), 5xx (Server Error). Specific examples include 200 OK, 404 Not Found, 500 Internal Server Error etc. The answer should list several examples from each category.

7. How do you handle exceptions in a REST API?

   • Answer: Using appropriate HTTP status codes to signal errors (e.g., 400 Bad Request, 404 Not Found, 500 Internal Server Error). Returning meaningful error messages in the response body, potentially using a standardized error format (e.g., JSON).

8. Explain different ways to implement authentication and authorization in a REST API.

   • Answer: Basic Authentication, OAuth 2.0, JWT (JSON Web Tokens), API keys, OpenID Connect. The answer should briefly describe each method and its pros and cons.

9. What are some common security considerations for REST APIs?

   • Answer: Input validation, output encoding, protection against SQL injection, cross-site scripting (XSS), cross-site request forgery (CSRF), rate limiting, proper authentication and authorization.

10. What are the advantages of using Spring Boot for building REST APIs?

    • Answer: Auto-configuration, simplified dependency management, embedded servers (Tomcat, Jetty), ease of testing, production-ready features (monitoring, security).

11. How to handle large datasets in a REST API?

    • Answer: Pagination, filtering, sorting, using efficient data formats (e.g., JSON), asynchronous processing, caching, database optimization.

12. Explain different ways to test a REST API.

    • Answer: Unit testing (testing individual components), integration testing (testing interactions between components), end-to-end testing (testing the entire system), using tools like Postman, JMeter, REST-assured.

13. What is versioning in a REST API and why is it important?

    • Answer: Versioning allows for backward compatibility when updating the API. Methods include URI versioning (e.g., /v1/users), header versioning, content negotiation (using Accept header). It is important to avoid breaking changes for existing clients.

14. What are some common design patterns used in REST API development?

    • Answer: Repository pattern, Factory pattern, Singleton pattern, DAO (Data Access Object) pattern, Template method pattern, Strategy pattern. The answer should briefly explain each pattern and its application in the context of REST APIs.

15. How do you handle concurrency in a REST API?

    • Answer: Threading models (e.g., ExecutorService), database transactions, optimistic locking, pessimistic locking, caching strategies.

16. What is Swagger/OpenAPI and how is it used?

    • Answer: Swagger/OpenAPI is a specification and set of tools for designing, building, documenting, and consuming RESTful web services. It generates interactive API documentation and client SDKs.

17. Describe your experience with different databases and their usage in REST API development.

    • Answer: This requires a personalized answer based on the candidate's experience. Examples: MySQL, PostgreSQL, MongoDB, Oracle, Cassandra. The answer should mention specific usage scenarios and technologies used for database interaction (e.g., JPA, Hibernate).

18. Explain your experience with message queues (e.g., RabbitMQ, Kafka) and their role in REST API development.

    • Answer: This requires a personalized answer based on the candidate's experience. Describe scenarios where message queues were used to decouple services, handle asynchronous operations, or improve scalability and performance of the REST API.

19. How do you ensure the scalability and performance of a REST API?

    • Answer: Load balancing, caching, database optimization, efficient algorithms, asynchronous processing, horizontal scaling, using appropriate technologies and infrastructure.

20. What is your experience with CI/CD pipelines for REST API development?

    • Answer: This requires a personalized answer describing experience with tools like Jenkins, GitLab CI, CircleCI, etc., and the process of automating build, testing, and deployment of REST APIs.

21. Explain your experience with containerization (Docker, Kubernetes) in REST API development.

    • Answer: This requires a personalized answer describing experience with containerizing REST APIs and deploying them to container orchestration platforms like Kubernetes. It should mention benefits like portability, scalability, and ease of deployment.

22. What are your preferred tools and technologies for REST API development?

    • Answer: This requires a personalized answer listing preferred IDEs (e.g., IntelliJ IDEA, Eclipse), build tools (e.g., Maven, Gradle), testing frameworks (e.g., JUnit, TestNG, Mockito), and other relevant tools.

23. How do you handle data validation in your REST APIs?

    • Answer: Using validation frameworks (e.g., Hibernate Validator), custom validation logic, input sanitization, checking data types and constraints.

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