Top 15 REST API Interview Q&A

Building web APIs, microservices, and other web services have become one of the basic business needs nowadays. And one of the most popular approaches to it is to use REST APIs. Of course, you can build some top-notch quality software using the best programming languages but when you are offering services, you are offering a package of such software applications or features built using a different programming language that works in sync to fulfill the requirements of the users. 

And to integrate this software, you have to use the REST API. of course you already know all of this. But delivering the same information when asked for or showing how it all works can be a little tough. And that’s why many developers tend to fail the interview. Although they are skilled enough, they don’t know what questions are going to be asked of them. Also, even if you know the answers, you are not sure about how to convey them.

And that’s why, in this blog, we are going to discuss some of the most important and frequent questions. 

REST API Interview Questions

1. What is a REST Resource?

A REST resource is a collection of resources that expose a defined set of operations (or methods) on an entity. The resources can be anything. They are usually organized into hierarchies, where each hierarchy represents an object with the same root and different “child” objects. These hierarchies are called “resources” in REST terminology because they represent items that may be accessed and manipulated by clients, such as web browsers or mobile app developers.

2. What are the features of RESTful Web Services?

The following are the features of RESTful Web Services:

  • It is a uniform interface for accessing resources.
  • A resource has properties and methods which can be identified by their names and definitions respectively.
  • Support for Uniform Access to Resources Over Distributed Networks
  • Hypertext-style Linking Using URLs (Uniform Resource Locators) between Resources
  • Use of Hypertext Transfer Protocol (HTTP) for Inter-Resource Communication
  • Separation of Concerns in Data Modeling – Use URIs to Represent Resources, Not Forms or RDFS Statements
  • The representations that are sent in response to a request can be in various formats and media types such as text/plain, application/XML, or any other format or media type.
  • The representation must be valid according to the HTTP protocol and syntax rules.
  • The representation must be cacheable and include appropriate header information so that the user agent may use it when revalidating subsequent requests on the same resource.

3. What is the concept of statelessness in REST?

RESTful web services are defined as being stateless. They do not require any state to be saved between requests. Also, to function properly, they don’t need any data related to the client  This allows for a very lightweight and fast response time, which is important for mobile devices.

4. What are the HTTP Methods?

HTTP methods are the ways that you can send information from your web server to your application. There are many methods but the most popular ones include GET, POST, PUT and DELETE. 

GET requests to send a representation of some data back to the client or browser. This is what we mean by “GET”. POST requests do not return data; they create something on the server side and then return it as an entity. This is what we mean by “POST”. 

PUT requests are similar to POST requests in that they create something on the server side, but they allow you to modify an existing resource on the server side. This is what we mean by “PUT”. DELETE is used to delete something from the server.

5. What are HTTP Status codes?

Every HTTP request has been allocated status and a way of determining that status is called HTTP status codes. They are returned in the response header field, but they can also be used in other places. 

The most common HTTP status code is 2xx (indicating success), although this is not necessarily true for every case. For example, a 400 Error Code means that something went wrong on your server, while a 404 means that there was nothing at all on the page you requested. 

6. What do you understand about JAX-RS?

JAX-RS is a standard for building Java web services that can be used in multiple programming languages. It’s not just for Java, but also for JavaScript and other languages that run on the server.

JAX-RS defines a set of annotations that you can use to tag your classes and methods with information about how they should be invoked, how they should be marshaled to/from the request/response, and other details. These annotations are called JAX-RS annotations.

One of the main goals of JRS is to enable easy integration of existing Java EE applications with third-party libraries written in other languages like Javascript or Ruby.

7. What is URI?

A string of characters that identifies the resource on the web uniquely is known as URI. A URI can be thought of as a hyperlink, which points to some other resource on the internet. For example, in this article, is a URI that instructs browsers and search engines what web page you want to go to when you click on it.

A URI has three parts:

The scheme (e.g., “HTTP”) tells the browser how to interpret this URL. In this case, “HTTP” means that the browser should use HTTP (Hypertext Transfer Protocol) to request information from this server.

The hostname (e.g., “”) provides information about the location of the server or domain where the resource lives (in this case).

The path (e.g., “/search”) tells the browser where in the directory hierarchy of this site you want it to look for this file (in this case).

8. What makes REST services to be easily scalable?

REST services are easy to scale because they don’t require complex software. The HTTP is just a simple request & response model which can be easily implemented in any system and application. It’s also very flexible, allowing custom headers, response codes, and bodies.

A REST service can be deployed on any server or cloud platform that supports the HTTP protocol. A REST service doesn’t need to be built from scratch; it can use existing code as long as it conforms to standards such as JSON and XML. REST services also have a very small footprint as there is no middleware layer added to them. 

The advantage of using REST services is that it allows developers to focus on building their applications without having to worry about scaling issues.

9. How can you test RESTful Web Services?

There are many ways to test RESTful web services. The most common approach is to use a browser-based test tool such as Selenium, PhantomJS, or SauceLabs. This will allow you to automate the interaction with the server and make sure that your code interacts correctly with the server.

Another way to test them is by using REST APIs, cURL, and Postman. The API here is used to interact with the servers. These tools make it easy for developers to use the API directly without having to write any code themselves.

Another option is to create a mock service that simulates the functionality of your real service. This allows you to make sure that your application behaves correctly even when interacting with a real service as if it were a mock service. For example, if you are building an online shopping cart system, it is important that users can add items to their cart without being charged for shipping costs or other third-party fees. You can create a mock service that simulates this functionality so that developers can test their applications without having to pay for shipping costs or other third-party fees. 

10. How does HTTP Basic Authentication work?

HTTP Basic Authentication is a means by which a server can authenticate a client, often in a multi-user environment. It is performed over the same connection as HTTP authentication, but the authentication scheme itself does not require the use of cookies or other means to sign on.

The basic idea behind HTTP Basic Authentication is that the user is presented with two options: “login” and “password.” The user enters their login information and then receives a cookie from the server containing unique identifying information.

If an attacker gains access to this cookie, they can impersonate any user who has successfully logged into the website using their login information. The attacker will also have access to all sessions that have been created using said cookie; however, they are unable to see or manipulate any session data beyond what was provided in addition to the initial login request.

11. What are the best practices for developing RESTful web services?

The best practices for developing RESTful web services are outlined in the following sections:

Use the HTTP verbs to define your resources – The HTTP verbs should be used to define your resources. The HTTP verbs are GET, DELETE, PUT and POST. These are the standard HTTP methods that you can use when creating RESTful web services.

Use the HTTP status codes – Using the HTTP status codes for your web services will help keep your clients informed about what is happening. It helps them understand what action they need to perform to get the response they want or expect from the application.

Use hypertext transfer protocol (HTTP) with content negotiation – You should use hypertext transfer protocol (HTTP) with content negotiation. This means that you can send a message containing multiple representations of one resource at once without having to make multiple requests for each representation request. You would only make one request instead of many as there would only be one response returned instead of many different responses returned as there would be if you were using traditional request-response-based interfaces such as those provided by Java RMI or CORBA. 

Use the same URL format for all requests and responses – This guarantees consistency in how a service receives requests from clients and how it responds to those requests. If you need to send data that doesn’t fit in a URL (for example, if you want to include parameters), use the Content-Type header instead of a URL parameter. 

12. What are Idempotent methods? How is it relevant in the RESTful web services domain?

Idempotent methods are those that can be called more than once without causing any side effects.

The use of idempotent methods is important in RESTful web services as they help to ensure that data is not duplicated or lost when it is shared with other users. For example, if a user calls a method that creates a new record, but then deletes it again after calling another method on the same object, this will result in two records being created and one being deleted. 

However, if the same method was called again after this sequence of events, a new record would be created and none of the old records would be deleted.

13. Can you tell what constitutes the core components of an HTTP Request?

The core components of an HTTP request are:

  • URL – The location or path to the resource being requested.
  • Request method – The type of request being made (GET, POST, etc).
  • Request headers – Additional information that can be sent along with the request. Typically set by web servers, but can also be specified in client-side code. These define the context of the resource being requested and allow for custom headers to be sent as part of the request.
  • Request body – A piece of data containing additional information about a resource that’s been requested. This can include HTML pages, images, style sheets, and more depending on the nature of the resource being requested.

14. What constitutes the core components of HTTP Response?

The HTTP response is a data object that is returned to the client when an HTTP request has been made. The response may be split into different components such as headers, body, and trailer. Headers consist of the data related to the request made by the users like server name, URL, port number, and request method. 

The Trailer is used to transfer the response message without breaking it into multiple lines of text. The body contains the actual data that needs to be sent back to the client.

15. What’s a real-world example of a REST API?

The real-world example I have in mind is Amazon Web Services (AWS). Amazon has several different APIs, each of which provides different functionality. For example:

  • Amazon Simple Storage Service (S3) provides storage for files and other data.
  • Amazon Simple Queue Service (SQS) provides queues for storing messages between systems.
  • Amazon Simple Notification Service (SNS) is similar to SQS but with notifications instead of queues.
  • Amazon DynamoDB is a database service that automatically manages consistency across multiple servers across regions and availability zones within regions. It also supports secondary indexes and full table scans.

Now the REST is up to you

The implementation of REST APIs is so common nowadays that even new developers are familiar with the concept. So it is a prerequisite that an experienced developer would already possess some insight into the matter. 

During such interviews, it is not necessary to stick to the textbook definition and other technicalities. You can mold your answers by adding a pinch of your experience with the subject of the question i.e. REST. This will show the interviewers that you not only possess the knowledge but are also capable enough to solve real-world problems with this powerful technology. So, good luck, and have fun out there!

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