Java REST API Interview Questions and Answers for freshers

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Java REST API Interview Questions for Freshers

  1. What is a REST API?

    • Answer: A RESTful API (Representational State Transfer Application Programming Interface) is an architectural style for building web services. It uses HTTP methods (GET, POST, PUT, DELETE) to interact with resources, identified by URIs, and typically uses formats like JSON or XML for data exchange. It's stateless, meaning each request contains all the information needed to process it.

  2. What is the difference between GET and POST requests?

    • Answer: GET requests retrieve data from a server, while POST requests submit data to be processed to the server. GET requests are typically idempotent (multiple calls have the same effect as one), while POST requests are not. GET requests are usually appended to the URL, while POST requests send data in the body.

  3. What is PUT and DELETE request?

    • Answer: PUT requests update an existing resource on the server, identified by the URI. It replaces the entire resource. DELETE requests delete a resource on the server, identified by the URI.

  4. Explain HTTP status codes and their significance.

    • Answer: HTTP status codes are three-digit codes that indicate the outcome of a client's request. Examples include 200 OK (success), 404 Not Found (resource not found), 500 Internal Server Error (server-side error). They're crucial for debugging and understanding the server's response.

  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 human-readable and easily parsed by both humans and machines, making it ideal for exchanging data between a client and a server in REST APIs.

  6. What is RESTful API Design Principles?

    • Answer: RESTful API design principles include: Client-Server architecture, Statelessness, Cacheability, Uniform Interface (using standard HTTP methods), Layered System, and Code on Demand (optional).

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

    • Answer: Spring Boot, Jersey, and RESTEasy are popular Java frameworks for building REST APIs. Spring Boot is particularly widely used due to its ease of use and extensive features.

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

    • Answer: Annotations like `@RestController`, `@RequestMapping`, `@GetMapping`, `@PostMapping`, `@PutMapping`, `@DeleteMapping`, `@PathVariable`, `@RequestBody`, and `@ResponseBody` are used in Spring to define REST controllers, map HTTP requests to methods, and handle request and response data.

  9. What is a Spring Boot Starter?

    • Answer: Spring Boot Starters are convenient dependency descriptors that simplify the inclusion of necessary libraries for specific functionalities, such as Spring Web for REST APIs. They reduce boilerplate configuration.

  10. How to handle exceptions in a REST API?

    • Answer: Use exception handling mechanisms like `@ControllerAdvice` in Spring to globally handle exceptions and return appropriate HTTP status codes and error messages in a consistent format (e.g., JSON) to the client.

  11. 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 and navigate the API without prior knowledge of its structure.

  12. Explain the concept of versioning a REST API.

    • 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, and content negotiation.

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

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

  14. What are the benefits of using Spring Data REST?

    • Answer: Spring Data REST simplifies the creation of REST APIs by automatically generating controllers based on JPA repositories. It reduces development time and boilerplate code.

  15. Explain the use of RequestParam and PathVariable annotations.

    • Answer: `@RequestParam` binds request parameters from the query string to method parameters, while `@PathVariable` extracts values from the URI path.

  16. How to handle different media types in a REST API?

    • Answer: Use `@Consumes` and `@Produces` annotations in Spring to specify which media types (e.g., `application/json`, `application/xml`) the API can accept and produce.

  17. What is Swagger/OpenAPI and how is it used in API development?

    • Answer: Swagger/OpenAPI is a specification and set of tools for describing and documenting REST APIs. It allows developers to generate interactive API documentation and client SDKs.

  18. Explain different ways to implement pagination in a REST API.

    • Answer: Pagination techniques include using query parameters like `limit` and `offset`, or using cursors to identify the next page of results.

  19. How to test a REST API?

    • Answer: Use tools like Postman, curl, or JUnit with RESTAssured to send requests to the API and verify the responses. Automated testing is crucial for ensuring quality.

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