In this article, we will help you to prepare for the API job. However, there are many of difficult question that is not answerable by the applicants. So here are some most important and common REST API Interview Questions asked by the interviewers in the API jobs interview.
REST API Interview Questions and Answers
- What is the elaboration of the term REST API?
REST stands for Representational State Transfer, and API refers to Application Programming Interface.
- What is an API?
An API refers to a set of definitions that build and integrate an application software. It is, in a way, a contract between the information provider and the one using it, as it establishes the contents required from the consumer and the content required by the producer. It could also be said that if one wants to interact with their computer system by performing a function or to retrieve information, the API helps to communicate to the system whatever the user wants so that the user can understand and fulfill the request.
- Define REST API.
REST refers to a set of architectural constraints or a software architectural style created or built to guide the designing and development of the architecture for the World Wide Web. REST explains a set of constraints for how the structural building of an Internet-scale system like the World Wide Web must function. The web services that conform with or work according to the REST API are known as RESTful services. So the REST API allows for interaction with these RESTful web services.
- Who created the REST API, and what was the sole reason behind its creation?
REST API was created by a Computer Scientist named Roy Fielding back in 2000. The sole purpose of creating it was to create a common standard that allowed any two servers in the world to communicate and exchange data. So, a set of architectural constraints or principles was defined, which they named REST. There were mostly universal rules around it since APIs had to be simpler and focus more on integrating more and more servers across the globe. To make APIs both more flexible and accessible was the goal of Roy Fielding.
- How does REST API represent the client request made via the RESTful API?
- What is a Resource, and is its REST API one?
A Resource is any information that can be named, be it an image or a document, or even a collection of other resources. It can be said to be an object with a type of relationship with other resources and methods that operate on it. They are identified with their URI. Yes, REST is a resource. REST also uses a resource identifier to identify a particular resource involved in the interaction between two components or parties exchanging information or data.
One more important thing that can be associated with REST is the resource methods. These are the methods that are to be used to perform the desired transaction of information. All the necessary things to change the resource must be a part of the API response for that resource – along with the methods and the state that they will leave the representation in.
- What are the architectural constraints of the REST API?
- API requests look the same no matter where they arrive from since the REST API has a uniform interface. The REST API makes sure that the same piece or chunk of data that has been received say the name or the email address of a user, belongs to one Uniform Resource Identifier or URI. Resources should contain all the information that the client needs and also should not be too big.
- The client and server applications in REST API design are completely independent of each other. The only information that the client application must know is the URI of the requested source. There is no other way in which it can interact with the server application. Similarly, a server application should not modify or make changes in the client application, so the sole purpose is just to pass it to the requested data via HTTP. So, the client and server go through the process of decoupling, which is defined as separation or disintegration. So the client and the server work as different units within their confined frame of work and are not able to modify any of the information.
- REST APIs have a feature called statelessness, which means that every request has to include all the data and information necessary to process it. REST APIs do not need any sessions from the server side. Server applications have no allowance for storing any data that is related to the client’s request.
- There is an available feature of cacheability on both the server’s and client’s sides. A cacheable feature allows for an HTTP response that can be cached or stored to be used or retrieved later, thereby saving a new request to the server. The servers also have to have information regarding if caching is allowed for the resource that has been delivered or not. Its aim is to improve the performance of the client, leading to greater scalability on the server’s side.
- The client and server applications may or may not connect directly to each other since there might be many intermediaries in the loop of communication, as a result of which the calls and responses have to go through a number of different layers. REST APIs are designed so that neither the client nor the server can tell if the communication is happening with the intermediary or the end application. As a result, it has a layered system of architecture in its structural foundation.
- REST APIs, in certain cases, develop a code only on command. Since they usually send static resources, but in smoke cases, the responses also have an executable code, as in the case of Java applets. In such times, the code runs only on demand.
- How does the REST API work?
REST APIs communicate through HTTP requests (HTTP is a protocol that allows fetching of resources, like HTML documents. It is the client-server protocol and is the basis or foundation of any form of data exchange on the Web.). REST API through HTTP protocols performs standard database functions like creation, reading, updating, and deleting records within a resource.
REST API calls and requests include important information that can be used to identify the user, such as authorizations made by the same, Uniform Resource Identifiers or URIs, caching, cookies accepted by them, etc. So request headers and parameters (these can be used to provide the information about the requester by using HTTP protocol) and the HTTP status codes are used with efficiently designed and built REST APIs.
- Do you think that the flexibility feature of REST API is also a flaw, and so what has been developed in order to overcome that flaw?
Although the flexibility allows it to be used more globally, with more and more servers connecting across the world and the usage of programming languages like JSON, which both humans and machines can understand alike, it still is a feature that might make the design of the API prove to be inefficient or simply poor or broken. For this very reason, the developers have tried their best to produce some specifications in the structure of the REST API.
The OpenAPI Specification or OAS allows for a user interface to be established in a way such that it allows any developer or application under the RESTful API cluster to discover it and fully be able to gauge the capabilities and the parameters it can reach, like for instance the available endpoints of the API, the operations that it is allowed to perform on each of the endpoints, the parameters of the operations or its implications and effects, and other information.
It has been updated now and then for better and efficient usage. The latest version to now is released OAS3, which includes tools like the OpenAPI generator, which helps in generating clients for API and server stubs (a stub is a kind of a code that converts the information or parameters that are exchanged between the client and the server during a remote procedure call or RPC) in different programming language formats.
- How to secure a REST API?
To secure a REST API, the starting point to be considered is the industry best practices like using algorithms to secure the password and HTTPS to secure data transmission and information. A framework for authorization called OAuth 2.0 can help limit any third-party or external applications. Another feature is that using a timestamp in the HTTP header also allows the API to reject any requests or commands made after a certain period of time, thereby upping the safety and security of the users.
Validating the parameters and JSON Web Tokens or JWTs (JWTs are compact means, protected by a URL) represent the claims to be transferred between two parties, generally client and server. They act as credentials that grant access to information resources.) are also ways that make sure that the API can only be accessed by authorized clients and not just anyone or a third party for that matter.
- Are REST API and HTTP the same? How are they different?
No, REST and HTTP are not the same. In REST, the architectural style or structure it has, the data in use, and the functionality of the API are considered resources (as mentioned above), and they are accessed using Uniform Resource Identifiers or URIs. These resources are acted upon with the use of some simple operations and commands. And the client and server’s exchange of information occurs using a standardized protocol, that is, HTTP. Resources undergo decoupling or disintegration from their representations.
Their content can be accessed in different formats according to the user’s convenience, such as HTML, XML, plain text, PDF, JPEG, JSON, etc. So, in conclusion, HTTP helps in the safe functioning of REST API but is not limited to that particular user only. HTTP or Hypertext Transfer Protocol is a communications protocol, so it is surely not limited just to the use of RESTful services. It has a major use, and the main use is to send and receive web pages and files on the internet.
- Can you name some of the shortcomings of the RESTful web services?
- There cannot be any asynchronous calls since it works on HTTP. Asynchronous calls refer to a method used in which the call returns immediately to the caller before the completion of the princess and without blocking the calling thread. So it offers more flexibility and allows the users to set the schedule and work at their own pace. HTTP, however, is a synchronous protocol in which the client issues a request and waits for a response. Hence asynchronous calls aren’t possible since RESTful services work on HTTP protocol.
- Due to the lack of a defined contract between the server and the client, the communication has to happen through other means like emails. The REST interface has useful documentation, but it still lacks a format that is unambiguous and preferably readable by a machine.
- Session cant is maintained because of the feature of statelessness, which is essentially the no storage of any data on this server across the requests. In other words, the server does not store any data about the state of the client session on the server’s side. The relevant session information is passed on to the server as needed and so sessions cannot be maintained.
- The security restrictions do not get imposed inherently by the REST API. The security protocols are inherited by implementing them. RESTful APIs are stateless, and so authentication requests shouldn’t be dependent on cookies or sessions, but an API request should come with some authentication credentials, which must be validated on the server for every request.