Java REST API Interview Questions and Answers

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100 Java REST API Interview Questions and Answers

  1. What is a REST API?

    • Answer: A REST (Representational State Transfer) API is an architectural style for building web services. It uses HTTP methods (GET, POST, PUT, DELETE) to interact with resources, identified by URIs. Key principles include statelessness, client-server architecture, cacheability, and a uniform interface.

  2. What are the HTTP methods used in REST?

    • Answer: GET (retrieve data), POST (create data), PUT (update data), DELETE (delete data), PATCH (partial update), HEAD (retrieve headers), OPTIONS (describe communication options).

  3. Explain RESTful constraints.

    • Answer: RESTful APIs adhere to constraints like client-server architecture, statelessness (each request contains all necessary information), cacheability (responses can be cached), uniform interface (standardized interaction), layered system (clients don't need to know the server's internal structure), and code on demand (optional, allows the server to extend client functionality).

  4. What is a resource in REST?

    • Answer: A resource is any entity or piece of data accessible through the API, identified by a URI (Uniform Resource Identifier).

  5. What is HATEOAS?

    • Answer: HATEOAS (Hypermedia As The Engine Of Application State) is a constraint of RESTful APIs. It means that responses include links to related resources, allowing the client to discover available actions and navigate the API dynamically without hardcoded URIs.

  6. What are the different status codes in HTTP? Give examples.

    • Answer: 1xx (Informational), 2xx (Successful), 3xx (Redirection), 4xx (Client Error - e.g., 400 Bad Request, 404 Not Found), 5xx (Server Error - e.g., 500 Internal Server Error).

  7. Explain the difference between GET and POST requests.

    • Answer: GET requests retrieve data; they are idempotent (multiple calls have the same effect) and should not have side effects. POST requests create or submit data; they are not idempotent and can have side effects.

  8. What is JAX-RS?

    • Answer: JAX-RS (Java API for RESTful Web Services) is a Java specification for creating RESTful web services. It provides annotations for mapping HTTP methods to Java methods.

  9. What are some popular JAX-RS implementations?

    • Answer: Jersey and RESTEasy are two widely used JAX-RS implementations.

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