Several developments, including cloud computing and microservices-based architecture, were made possible by RESTful APIs. They have portrayed online communication and computing as being simple. Therefore, any developer must understand what REST is, how it functions, its benefits, and how to create safe services to keep up with the times. As they may assist them in creating solutions that are scalable, simple to maintain, and enable their products to reach out to the entire globe thanks to the power of the internet, many businesses prefer developers with REST understanding.

The most frequent REST API interview questions regarding RESTful web services during REST API interviews, and inquiries regarding the JAX-RS library and RESTful web services built using the Spring MVC framework, are mentioned in the section below. Before sitting or scheduling an interview, preparing for all mentioned REST API interview questions is crucial.

What is REST?

REST, describing the Representational State Transfer, is responsible for developing website apps established on the HTTP protocol. REST specifies several rules that website-related usefulness must attach to believe it. The suggestions ensure standardized HTTP methods among the server and user to transmit submissions virtually.

REST API

What is a REST API?

The RESTful API makes safe online information exchange between two computer systems. To complete a variety of activities, the majority of business applications exchange data with other internal and external programs. For example, when your internal system of accounts shares employee information with the outer bank system for generating pay slips. It can be done with REST API as this information are individual personal, and REST API software standards are secure, efficient, and trustworthy.

RESTful API is known as API that is linked to REST in some way. All data are considered resources in REST API and & determined by a precise standard constant unit called (URI). The Twitter API creates a tweet as a resource that the user may access and retrieve. Using the Twitter API, users can publish tweets easily.

What are the principles of REST?

Client-server allows a sequence of responses that are utilized to transmit between the consumer and server. Both can send and accept responses from one another. This clear vision of the client-server method will allow both forces to operate unassisted from each other.

Layered System

Between the client and API server, layers are servers. These different servers perform several tasks, such as detecting spam and enhancing performance. The messages sent between the client and the application programming interface (API) server are unaffected by adding or removing layers because REST (representational state) uses modular architecture.

Uniform interface

The client and server must always use the identical protocol for all communications. This protocol is HTTP REST. Because every application uses the same language to request and provide data, a uniform interface facilitates integrations.

Stateless

In stateless communication, the server keeps no records of the responses that have already been sent. Every response possesses the complete input needed to conclude the dealings. It improves interpretation by decreasing server load and memory usage. It also withdraws the chance that a request may fail because of incomplete information.

Cacheable

Clients can cache any resources to increase performance by using server answers from servers that indicate whether or not a resource is cacheable. REST also contains the following optional condition.

Code-on-Demand

An API's response can contain executable code that users can run. Thus, the client application can execute the code on its own back end.

What is the difference between AJAX and REST?

The difference between AJAX and REST is:

AJAXREST
XMLHttpRequest objects are used in Ajax for sending requests to the server. However, the code from JavaScript provides the answers to dynamically change the current page.The utilization of resources is important to the URI structure and request/response pattern. used by REST.
Ajax is a group of technologies that allows the dynamic updating of the user interface without the page to be reloaded.Users can request data or information from servers using the REST software architecture style.
Ajax eliminates asynchronous communication between the server and the user.REST demands communication between the server and the user.

How does Microservice Architecture work?

An architectural method for developing cloud applications is called microservices. Each application is composed of a number of services, each of which executes in a separate process and interacts with the others via APIs. A method of creating applications known as a "microservices architecture" has become a best practice over time. The components of the microservice architecture are based on the needs of the business.

  • Clients

Requests are sent by numerous users using various devices.

  • Identity providers

Verify the identities of users or customers and provide security tokens.

  • API gateway

Client requests are handled via API Gateway.

  • Static content

All of the system's material is contained in static content.

  • Management

Determines failures and balances services across nodes.

  • Service discovery

A tool for determining the path of communication between microservices.

  • Content delivery network

A distributed network of proxy servers and associated data centers.

  • Remote service

Information stored on a network of IT devices can be accessed remotely with the help of a remote service.

Microservice Architecture

What are the HTTP methods supported by REST?

The REST HTTP supported methods are:

  • GET - the most extensively used method in websites and APIs, GET receives resources from the specific data server.
  • POST - through the POST method, data is sent to the API server to update the resource. When a server receives the data, it stores it in the HTTP request body.
  • PUT - it sends data to API in order to create and update the resources.
  • DELETE - as the name suggests, this method is used to delete the resources at specific URLs.
  • OPTIONS - it details the supported techniques.

HEAD - the metadata about the request URL is returned. Let's examine the situation from the viewpoint of a single record. Say there was a record for a worker with employee number 1. The following activities would each indicate something different.

POST - since we are retrieving information for employee 1, who has already been created, this is not applicable.

GET - this would be used to retrieve the employee's information via the RESTful web API, and the employee number would be 1.

PUT - using the RESTful web API, PUT would be used to update the employee's information to reflect Employee No. 1.

DELETE - this function is used to remove the employee's information with employee number 1.

What is the difference between PUT and POST?

The difference between PUT and Post is as follows:

  • PUT - precisely and particularly identifies a file or resource at a provided (uniform resource identifier) URI. PUT alters an existing file if it exists at that uniform resource identifier - URI. PUT forms a file if there exists one already.Plus, PUT is idempotent, suggesting it does not impact files yet how frequently it is used.
  • POST - it sends data to a distinct uniform resource identifier - URI and expects that the resource file there will manage the demand. At this moment, the website server can decide what can be done with the data in the context of the selected file. Plus, the POST strategy is not idempotent, which means that if you utilize it more than once, it will resume generating new files.

What is the difference between Monolithic SOA, and Microservices Architecture?

Monolithic apps have a very slow rate of development and are made up of interconnected, indivisible units. Smaller, minimally connected services make up SOA, which also has limited development.

Microservices are incredibly small, loosely connected, standalone services with a rapid iterative development cycle.

What is URI?

A Uniform resource identifier is referred to as a URI. A URI in REST is a string that designates a web server's resource. Each resource has a distinct URI that, when used in an HTTP request, enables clients to target it and do actions on it. Addressing is the process of directing traffic to a resource using its URI.

The format of URI is:

<protocol>://<service-name>/<ResourceType>/<ResourceID>

There are two types of URI

1. URL - the information about retrieving a resource from its location is available in the Uniform Resource Locator.

URLs contain information about the network hostname (sampleServer.com) and the path to the content (/samplePage.html), and they begin with a protocol (such as FTP, HTTP, etc.). It may also have search criteria.

2. URN - by using a name that is both distinctive and durable, a uniform resource name identifies the resource.

The location of the resource on the internet is not necessarily specified by the URN. They serve as models for other parsers to employ when identifying resources.

Whenever a URN identifies a document, it can be quickly converted into a URL using "resolver" so that it can then be downloaded.

What are the features of RESTful Web Services?

These features are present in every RESTful web service:

  • The Client-Server communication model is the foundation of the service.
  • The service utilizes the HTTP Protocol to fetch data/resources, run queries, and do other tasks.
  • "Messaging" is the method used to communicate between the client and the server.
  • The service can access resources via using URIs.
  • It adheres to the statelessness idea, in which the client's request and answer are not dependent on others, and so offers complete certainty that the necessary data will be obtained.
  • To reduce server calls for the same type of repetitive requests, these services also employ the idea of caching.
  • These services can also implement the REST architectural pattern using SOAP services.

What are HTTP Status codes?

Standard codes used in HTTP status correspond to established server task completion statuses. For instance, HTTP Status 404 indicates that the server does not have the requested resource.

HTTP Status codes

Let's look at the HTTP status codes and understand their meaning:

  • 200 - OK, success is evident.
  • 201 - when a POST or PUT request successfully creates a resource, the response code is 201 - CREATED. Using the location header, return the URL to the newly generated resource.
  • 304 - in the case of conditional GET requests, the status code 304 NOT MODIFIED is utilized to save network bandwidth. Response bodies must be void. Dates, locations, and other information should be in the headers.
  • 400 - BAD REQUEST indicates that invalid input, such as missing data or a validation mistake, has been provided.
  • 401 - FORBIDDEN indicates that the user does not have access to the method being used, such as deleting access without administrator rights.
  • 404 - ERROR indicates that the requested method cannot be found.
  • 409 - CONFLICTS When the method is executed, it indicates a conflicting issue, such as inserting duplicate entries.
  • 500 - INTERNAL SERVER ERROR code indicates that the server threw an exception while the method was being executed.

Can you tell me the disadvantages of RESTful web services?

RESTful web services' disadvantages are:

  • Sessions in RESTful web services are unable to be maintained since the assistant stick to the concept of statelessness.
  • Security and protection restrictions are not essential to REST. Some protocols are utilized for safety safeguards. Doing that will provide a warning that can employ while determining which protection and safety standards to choose, for example - SSL/TLS authentications.

Differentiate between SOAP and REST?

The difference between SOAP and REST is:

SOAPREST
A protocol called SOAP is used to implement web servicesREST is an architectural design pattern to develop web services
The guidelines provided by SOAP are intended to be strictly adhered toREST outlines criteria, however, they do not need to be fully adhered to
Since the SOAP client and server are more closely related, it is comparable to desktop programs with stringent contracts in this regardThe REST client is more adaptable than a browser and is independent of the server's design as long as it complies with the necessary communication standards
Only XML transfer between the client and the server is supported by SOAPMultiple data types, including XML, JSON, MIME, Text, etc., are provided by REST
SOAP Reads cannot be cachedREST Read queries can be cached
Service interfaces are used by SOAP to expose resource logicThe resource logic is exposed using REST using URI
SOAP is slowerREST is faster
Being a protocol, SOAP establishes its own security protocolsREST only takes on security precautions based on the implementation protocol
Although SOAP is not frequently chosen, it is utilized when stateful data transport and greater reliability are requiredThese days, REST is frequently preferred by developers since it offers more scalability and maintainability

What constitutes the core components of HTTP Response?

The HTTP response has four major components that are following:

  • Response Status Code - this displays the server's status code in response to the resource request. Example: A client-side error is represented by 400, whereas a successful answer is represented by 200.
  • HTTP version - the HTTP protocol version is indicated by the HTTP version.
  • Response Header - the response message's metadata is contained in this section. Data can be used to provide things like content length, type, response date, server type, etc.
  • Response body - the resource or message that the server actually returned is contained in the response body.

What are the differences between WebSockets and REST?

Here are some differences between WebSockets and REST mentioned below:

REST is based on CRUD operations, whereas WebSocket is a low-level protocol based on the concepts of socket and port, which are the fundamental transport mechanism.

While RESTful applications must design their operations based on verbs and HTTP, WebSocket demands the use of IP address and Port information, which are lower-level details for any application. WebSocket is a stateful protocol, while REST is built on a stateless protocol, meaning that neither the client nor the server need be aware of one another.

In contrast to REST, which is based on HTTP, which can scale horizontally, WebSocket connections can scale vertically on a single server. REST-based communication is comparatively more expensive, but WebSocket communication is less expensive.

Can we implement transport layer security (TLS) in REST?

We can, Yes! The communication of the client-server in REST is encrypted using TLS, which also provides the user the capability to ascertain the server. Since it replaces the Secure Socket Layer (SSL), it is a form of secure communication between the user and server. Since HTTPS functions well with the Secure Socket Layer (SSL) & Transport Layer Security (TLS), it is useful when creating RESTful web services. Here, it's important to note that the REST comes into the aspects of the protocol it uses. Therefore, the safety protections rely on REST's protocol.

What is the maximum payload size that can be sent in POST methods?

The magnitude of the payload that can be conveyed in the post method is theoretically unrestricted. However, it's important to remember that larger payloads will consume more bandwidth and take longer to process, affecting the server's responsiveness.

List the key annotations that are present in the JAX-RS API

  • Path - this details the REST resource's relative Uniform Resource Identifier (URI) path.
  • GET - this designator for the request method corresponds to HTTP GET. They handle GET queries.
  • POST - this designator for the request method corresponds to HTTP POST. They deal with POST inquiries.
  • PUT - this designator for the request method corresponds to HTTP PUT requests. They deal with PUT inquiries.
  • DELETE - it is defined as the designator for the request method used for HTTP DELETE. They handle the DELETE requests.
  • HEAD - this designator for the request method corresponds to HTTP HEAD. They deal with HEAD inquiries.
  • PathParam - developers can use this Uniform Resource Identifier (URI) path parameter to extract parameters from URIs for resource classes/methods.
  • QueryParam - the resource class/methods can use these queries that were extracted from the Uniform Resource Identifier (URI) by the developer using this Uniform Resource Identifier (URI) query parameter.
  • Produces - the MIME resource presentations that are created and sent to the user as a reply are specified here.
  • Consumes - this details the MIME resource presentations that the server will accept or use when receiving them back from the user.

Define RestTemplate in Spring

The primary class for user access to RESTful services is called RestTemplate. Utilizing REST restrictions, communication with the server is made. This is comparable to different template sections offered by Spring, such as JdbcTemplate and HibernateTemplate. The RestTemplate gives the methods the ability to communicate using the (Uniform Resource Identifier ) URI template, URI (Uniform Resource Identifier) path params, request/response kinds, request objects, etc. It provides high-level implementation details for HTTP Methods like GET, POST, PUT, etc.

This section from Spring 4.3 offers often-used annotations like @GetMapping, PutMapping, @PostMapping, etc. Before that, Spring offers the @RequestMapping interpretation to specify the methods being utilized.

What is the use of @RequestMapping?

RequestMapping

  • Requests are mapped to particular handler methods using the annotation.
  • Dispatcher Servlet manages all incoming web application routing in Spring. By using request handlers, it decides which controller among all is intended to handle the request when it receives it. All classes with the @Controller annotation are scanned by the Dispatcher Servlet.
    The @RequestMapping annotations, which are defined inside the controller methods and classes, are essential to the request routing process.

List out the tools or API for developing or testing web API

With the help of various tools like Postman, Swagger, etc., RESTful web services may be tested. Postman has many features, including the ability to send requests to endpoints, display responses that can be converted to JSON or XML, and analyze request parameters like headers and query parameters, as well as response headers. Like Postman, Swagger offers a number of functionalities as well as the ability to document endpoints. We can also test the performance and load of APIs using tools like Jmeter.

What is Caching?

When a server response is cached, it is saved so that a fresh copy can be utilized whenever necessary instead of having to generate the same response again. This technique not only lightens the burden on the server but also improves its performance and scalability. The response can only be cached by the client and only for a short while.

The resources' header and a concise description are included below so that the caching procedure can identify them:

  • Date and time the resource was created
  • Date and time of resource update, which typically keeps the most recent information
  • Header for cache-control
  • Date and time that the cached resource will stop working
  • The age that establishes the starting point for when the resource was fetched

What are the best resources to learn REST API?

There are many available resources to learn REST API for developing websites and mobile applications. The top 5 are listed below:

RESTful Web Services

In order to start out the development of an application with API consumption, this guidebook called RESTful Web Services wonder by Leonard Richardson will be a great asset in this regard. Especially if you are a beginner and want to understand the basics of Representational State Transfer (REST) website services. The resource revealed how Representational State Transfer (REST) functions and multiple other essential web-related services with examples. It is not based on any one programming language, so the understanding of RESTful APIs will not be bound to any programming language.

REST API Tutorial

REST API Tutorial is a great online resource for learning the Representational State Transfer (REST) if you are not a book or reading person. This resource will help you learn REST from start to end, covering all the basic aspects. This tutorial begins with the introduction of Representational State Transfer (REST), then will follow the path of examples concerning HTTP-related strategies and knowledge, and so on.

REST API Design Rulebook

This is also a great resource book for Representational State Transfer (REST) guidance as the author of the book Mark Masse transmits his experiences and strategies he has taken that helped with his application building using REST API. In this resource, he discussed practices for devising the application URIs, approaches for transmitting metadata via HTTP headers, and what types of media can be used. Furthermore, how to involve innovation in designing HTTP's submission methods and response status codes.

API Developer Weekly Newsletter

There is an awesome resource called the API developer weekly newsletter; it is an up-to-date resource for learning RESTful API as it is highly concentrated on API technique, structure, expansion, and architecture for web-based applications and mobile apps. The newsletter is specially designed for developers, project managers, and architects.

REST-Assured

This one is a fortunate, open-source REST testing medium for people experienced with one programming language called Java. This resource facilitates the procedure of testing and validating RESTful API processes. REST-Assured also eradicates the necessity to make boilerplate code for testing complex reactions and helps BDD syntax.

In a nutshell

To be conclusive, the above-mentioned article shares the REST API interview questions. It covers all the REST API interview questions for people who are going to apply or have applied for similar jobs that require RESTful API knowledge. These are the most common questions an interviewer can ask you during the job interview. Also, check out the mentioned resources before you sit for a final interview.

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