Java REST API Interview Questions and Answers for internship

1. What is a REST API?

   • Answer: A REST API (Representational State Transfer Application Programming Interface) is a set of architectural constraints for building web services. It uses standard HTTP methods (GET, POST, PUT, DELETE) to interact with resources, identified by URIs. It's stateless, meaning each request contains all the information needed to process it, and it relies on a client-server architecture.

2. Explain the difference between GET and POST requests.

   • Answer: GET requests are used to retrieve data from a server. They are idempotent (making the same request multiple times has the same effect as making it once), and the data is typically included in the URL. POST requests are used to send data to the server to create or update a resource. They are not idempotent and the data is sent in the request body.

3. What is HTTP status code 200 OK?

   • Answer: HTTP status code 200 OK indicates that the request was successful. The server successfully fulfilled the request.

4. What is HTTP status code 404 Not Found?

   • Answer: HTTP status code 404 Not Found indicates that the server could not find the requested resource.

5. What is JSON and why is it commonly used in REST APIs?

   • Answer: JSON (JavaScript Object Notation) is a lightweight data-interchange format. It's commonly used in REST APIs because it's human-readable, easy to parse by both client and server applications, and widely supported by programming languages.

6. What is XML and how does it compare to JSON?

   • Answer: XML (Extensible Markup Language) is another data interchange format, but it's more verbose than JSON. JSON is generally preferred in REST APIs due to its simplicity and smaller size, leading to faster data transfer.

7. What are HTTP headers? Give some examples.

   • Answer: HTTP headers provide additional information about the request or response. Examples include `Content-Type` (specifying the data format), `Authorization` (containing authentication credentials), `Cache-Control` (controlling caching), and `Accept` (specifying acceptable response formats).

8. Explain RESTful principles.

   • Answer: Key RESTful principles include: Client-server architecture, statelessness, cacheability, uniform interface (using standard HTTP methods), layered system, and code on demand (optional).

9. What is Spring Boot?

   • Answer: Spring Boot is a framework that simplifies the development of Spring-based applications, including REST APIs. It provides auto-configuration, starter dependencies, and embedded servers, making it easier to build and deploy applications quickly.

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

    • Answer: Exceptions should be handled gracefully by returning appropriate HTTP status codes (e.g., 400 Bad Request, 500 Internal Server Error) and providing informative error messages in the response body. Using exception handlers or custom error controllers is common practice.

11. What is Swagger/OpenAPI?

    • Answer: Swagger/OpenAPI is a specification for describing REST APIs. It allows you to define the API's endpoints, request/response formats, and other metadata. Tools then use this specification to generate documentation and client SDKs.

12. What is HATEOAS?

    • Answer: HATEOAS (Hypermedia as the Engine of Application State) is a REST architectural constraint where the API responses include links to related resources, allowing clients to discover available actions without hardcoding URLs.

13. Explain the concept of versioning a REST API.

    • Answer: API versioning is crucial for maintaining backward compatibility as the API evolves. Common techniques include URI versioning (e.g., `/v1/users`), header versioning (using a custom header), and content negotiation (using Accept headers).

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

    • Answer: Security concerns include authentication (verifying user identity), authorization (controlling access to resources), input validation (preventing injection attacks), HTTPS (using secure connections), and protection against common vulnerabilities like cross-site scripting (XSS) and cross-site request forgery (CSRF).

15. How would you implement authentication in a REST API?

    • Answer: Common authentication methods include API keys, OAuth 2.0, JWT (JSON Web Tokens), and basic authentication. The choice depends on the specific security requirements and context.

16. What is rate limiting in a REST API? Why is it important?

    • Answer: Rate limiting restricts the number of requests a client can make within a given time period. It's crucial for preventing abuse, denial-of-service attacks, and ensuring fair access to the API for all users.

17. How do you handle large datasets in a REST API?

    • Answer: Techniques for handling large datasets include pagination (returning data in smaller chunks), filtering (allowing clients to request specific subsets of data), and using efficient data formats (e.g., optimized JSON).

18. What is caching and how can it improve REST API performance?

    • Answer: Caching stores frequently accessed data in memory or a cache server, reducing the need to hit the database or perform complex computations on every request. It significantly improves response times and reduces server load.

19. What is the difference between a microservice architecture and a monolithic architecture?

    • Answer: A monolithic architecture is a single, self-contained application. A microservice architecture breaks down the application into smaller, independent services that communicate with each other. Microservices offer better scalability, maintainability, and fault isolation.

20. What are some tools you've used for testing REST APIs?

    • Answer: Popular tools include Postman, curl, JMeter, and REST-assured (a Java testing library).

21. Describe your experience with Git and version control.

    • Answer: [Describe your experience with Git, including branching, merging, pull requests, etc.]

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

    • Answer: Common patterns include the Repository pattern (for data access), the Factory pattern (for object creation), and the Singleton pattern (for managing shared resources).

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

    • Answer: Techniques for managing concurrency include using thread pools, asynchronous programming, and database transactions to ensure data consistency and prevent race conditions.

24. Explain your understanding of REST API documentation.

    • Answer: Good API documentation is crucial. It should clearly explain endpoints, request/response formats, authentication methods, error handling, and usage examples. Tools like Swagger/OpenAPI help generate documentation automatically.

25. What is your experience with databases and how do they relate to REST APIs?

    • Answer: [Describe your database experience. REST APIs typically interact with databases to store and retrieve data. The choice of database depends on the application's needs. Common choices include relational databases (like MySQL, PostgreSQL) and NoSQL databases (like MongoDB).]

26. How would you approach debugging a REST API?

    • Answer: Debugging strategies include using logging, debugging tools (like IDE debuggers), network monitoring tools, and examining HTTP requests/responses.

27. What are your strengths and weaknesses as a developer?

    • Answer: [Give a honest and thoughtful answer. Focus on relevant technical skills and soft skills.]

28. Why are you interested in this internship?

    • Answer: [Explain your interest in the company, the team, and the specific project or technology.]

29. Where do you see yourself in 5 years?

    • Answer: [Express ambition and a desire for growth, but also realism.]

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