REST API Interview Questions and Answers

Rest API is a powerful and popular technology for developing efficient and secure web applications. It is the de facto standard for designing and building distributed communication protocols over the Internet. Rest API Interview Questions is a comprehensive course designed to help prepare applicants for interviews involving Rest APIs distributed category-wise into different sections from beginner level to intermediate to expert levels. It covers basic concepts such as authentication and authorization and more advanced topics like data modeling and resource ownership. This course also focuses on providing a wide range of practical questions from different industries so candidates can practice common scenarios in a real-world setting. By the end of this course, applicants should have the skills and confidence to easily answer even the most difficult questions. With its focus on comprehensive application, this course is ideal for anyone looking to ace their next Rest API job interview.

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REST, or Representational State Transfer is an architectural style for distributed systems, and is typically used in reference to web services. The main idea behind REST is that instead of having different URLs for different actions (e.g. /login, /logout, /addUser), you only have one URL which represents a resource (e.g. /users).  

Then, the action is specified by the HTTP method used on that resource. For example, to login, you would use the POST method on the /users resource; to logout, you would use the DELETE method; and to add a user, you would use the PUT method. This makes for a much more concise and consistent API.

RESTFUL is just a slightly more specific variation of REST - it simply means that the server responds with JSON data instead of HTML data. JSON, or JavaScript Object Notation, is a standard format for data exchange which is more lightweight than XML and easier to parse. So a RESTFUL API would be one that adheres to the REST constraints described above, and also responds with JSON data.

Rest is helpful in building an API that is both flexible and easy to use. Its simple design principles and RESTful services can be quickly built and deployed without a lot of fuss. In addition, because they return data in a standard format, they can be easily consumed by a wide range of clients.

Expect to come across this popular question in REST API testing interview questions.

REST is an architectural style for networked systems and is a way to achieve scalability and Performance by grouping resources under a uniform interface. REST is not a standard but rather a set of constraints that enable us to build scalable RESTful web services when applied to our architecture. Its main principles are:

  • Client-Server Communication: This principle is the foundation of the web as we know it today. It basically states that there should be a separation between the client, which makes requests to the server, and the server, which responds to those requests. This separation of concerns allows us to build scalable web services that can be easily extended without affecting the clients.
  • Statelessness: This constraint dictates that each request from a client must contain all the information necessary for the server to understand and process it. In other words, the server cannot store any information about past requests from that particular client. This makes web services much easier to scale because each request can be processed independently of any other request.
  • Cacheability: This principle specifies that responses from a web service must be cacheable so that they can be reused by clients without having to send another request to the server. This helps improve performance by reducing the number of round trips between the client and server.
  • Uniform Interface: This constraint enables us to decouple our web services from our clients by providing a well-defined interface between them. As the interface should be simple, consistent, and easy to use, the most common way to achieve this is through the use of HTTP methods (GET, POST, PUT, DELETE).
  • Layered System: This constraint stipulates that we should be able to implement our web service as a set of distinct layers, each providing a different functionality level.  

By following these principles, we can create scalable and performant web services that are easy to extend and maintain.

When working with a REST API, we usually get back a response code that indicates whether the request was successful. Some of the most common response codes are:

  • 200 OK - This code means that your request was successful and the server was able to process it.
  • 201 Created - This code means that your request resulted in a new resource being created, such as a new user or a new blog post.
  • 202 Accepted - This code means that your request has been accepted by the server but has not been processed yet.
  • 400 Bad Request - This code means that your request was invalid or could not be understood by the server.
  • 401 Unauthorized - This code means that you are not authorized to make the request, and you need to provide authentication credentials.
  • 403 Forbidden - This code means that you are not allowed to access the requested resource, even if you are authenticated.
  • 404 Not Found - This code means that the requested resource could not be found on the server.
  • 500 Internal Server Error - This code means that there was an error on the server and your request could not be processed.
  • 502 Bad Gateway - This means that there was an error while trying to connect to another server that your request depends on.
  • 503 Service Unavailable - This means that the server is currently unavailable, usually due to maintenance or high traffic.
  • 504 Gateway Timeout - This means that there was a timeout while trying to connect to another server that your request depends on.

The 3 core components of an HTTP response are the status code, the headers, and the body.

The status code is a numeric value that indicates the status of the request. The most common status codes are 200 (OK), 404 (Not Found), and 500 (Internal Server Error).

The headers contain information about the response, such as the content type and length. They also provide an opportunity to set cookies and cache directives.

The body is the main part of the response and contains the data that was requested. Depending on the content type, it may be displayed inline or in a separate window. Common content types include text/html, image/jpeg, and application/json.

The main difference between the POST and PUT methods is that POST is used to create resources, while PUT is used to update them. When you use POST to create a resource, you're basically telling the server to allocate a new resource and return it to you. On the other hand, when you use PUT to update a resource, you're telling the server to find an existing resource and modify it according to the data you provide.

Another key difference between the two methods is that with POST, you can create multiple resources with the same data, while with PUT, each resource must be unique. This is because when you use PUT to update a resource, the server needs to be able to identify the exact resource you want to modify. With POST, on the other hand, the server simply creates a new resource based on the data you provide, without needing to identify an existing resource.

Overall, POST is more flexible than PUT, but PUT is more suited for updating existing resources.

Idempotent methods are HTTP methods that can be called multiple times without changing the state of the server. This is useful because it means that if a client makes a request and doesn't receive a response, they can simply retry the request and be confident that they will get the same response back.  

The main Idempotent methods are GET, PUT, and DELETE. HEAD and OPTIONS are also Idempotent, but this is less relevant because they don't actually change the state of the server. POST is not Idempotent because each time it is called, it creates a new resource on the server. One way to think of this is that Idempotent methods are safe to call multiple times, while non-Idempotent methods are not.

In RESTful web services, payload refers to the data that is sent to the server along with a request. This data can be in the form of parameters, headers, or a body. The type of payload that is sent will depend on the type of request that is being made. For example, when making a GET request, only headers and parameters are typically sent in the payload.  

However, when making a POST request, a body may be included in the payload containing information about what is being created or updated. Payloads are an important part of RESTful web services as they provide a way to send data to the server for processing.

While REST web services have a number of advantages, there are also some potential disadvantages to keep in mind. One issue is that REST can be less scalable than other web service architectures, since it relies on a client/server model. This means that each client request requires a separate server response, which can strain resources as the number of users grows. In addition, REST web services are often stateless, which can make session management more difficult.  

Finally, RESTful web services can be more complex to develop than other types of web services, since they often require a greater understanding of HTTP and XML. While these challenges should not be ignored, they should not deter you from using RESTful web services when they are the best option for your needs.

JAX-RS (Java API for RESTful Web Services) is a set of Java programming language APIs that provides support in creating web services according to the Representational State Transfer (REST) architectural pattern. JAX-RS uses annotations, introduced in Java SE 6, to simplify the development and deployment of web service clients and endpoints. This question tests your understanding of JAX-RS and its capabilities.  

A good response would discuss the advantages of using JAX-RS over other web service frameworks and how it can be used to create both simple and complex web services. Candidates should also be familiar with the most important annotations used in JAX-RS, such as @Path, @GET, @POST, @PUT, and @DELETE. A thorough understanding of JAX-RS will go a long way in impressing potential employers during an interview.

Statelessness is a key principle of the REST architectural style. It means that each request from a client should contain all the information necessary to process that request, and that the server should not maintain any state information between requests. This allows RESTful applications to be scalable and resilient, as there is no need to maintain complex session state on the server. It also makes it easy to cache data, as the same request will always return the same result.  

However, statelessness does not mean that the server cannot maintain any state at all; for example, a server may store information about which resources are available, and it may also keep track of security credentials for clients. However, all of this state information should be stored on the client, not on the server.

It's no surprise that this one pops up often in REST API questions.

Representational State Transfer (REST) is a stateless architecture in which clients can access and manipulate resources on a server. Each resource is identified by a Uniform Resource Identifier (URI) and can be accessed using a simple HTTP request. JAXB stands for Java Architecture for XML Binding. It is a Java standard that defines how to convert between XML and Java objects. JAXB provides an easy way to map Java classes to XML representations. JAXB can be used to create web services that comply with the REST architecture.  

When a JAXB object is marshaled to XML, it produces a representation of the object that can be sent to a client via HTTP. The client can then use the URI to access the resource and retrieve the XML representation. This allows clients to manipulate resources on the server without having to understand the underlying data model. By using JAXB, web services can provide a RESTful interface that is both simple and powerful.

Messaging, in terms of RESTful web services, is the ability to exchange messages between two systems quickly and efficiently. Messaging refers to an asynchronous communication paradigm commonly used in distributed systems. With messaging, one system can publish a message, which is then stored and sent by the message broker. The second system can then receive this message and process it accordingly.  

It's important to note that this type of communication is not limited to simple text messages but can also be used to send more complicated data such as images or CMYK color swatches. In addition, other methods such as point-to-point messaging or publish-subscribe messaging can also be used in this context depending on the requirements of the particular application. When working with a REST API it's important to ensure that you understand the concept of messaging and how best to use it for your web service applications.

A common question in interview questions for REST API, don't miss this one.

When it comes to developing a RESTful web API, having an understanding of different markup languages is crucial. Among the most popular are Hypertext Markup Language (HTML), the Extensible Markup Language (XML), JavaScript Object Notation (JSON), and YAML Ain't Markup Language (YAML). HTML is perhaps the most widely used for structuring information intended for display in a web browser. XML, on the other hand, is used to generate data that both computers and humans can read.  

JSON is often used to send data between client and server as its structure consists of plural objects, each containing key-value pairs. Lastly, YAML is great for storing hierarchical data as it uses indentation rather than tags like XML.  

Ultimately, what mark-up language should be used will depend on various factors such as the size of data, caching and complexity of the application. However, regardless of choice made, familiarity with these markups will prove to be invaluable when building a reliable REST API.

Knowing the different HTTP status codes is an important part of working with a REST API. An HTTP status code is a response from an HTTP server to the client, and it can range from 1xx (not functional) to 5xx (server error). Status codes such as 200, 301, and 404 are some of the most common that you may run into when using a REST API.  

A 200 code indicates that the request was successful in getting a valid response, while a 301 means that the URL has been moved permanently. A 404 means that the requested resource could not be found on the server. It's also important to pay attention to 3xx status codes; these indicate redirection, which can cause issues if done incorrectly. Understanding what each of these codes mean and how they may impact your application will help ensure its continued success.

Cache-control headers are a key element of REST APIs as they determine how long a given resource/data can be cached for and if any particular caching mechanism needs to be used in order to properly store the data. These headers help developers control the amount of data sent over a network, speed up response times, and reduce the need for expensive server resources. They can be set at the development level or within client requests, depending on the desired functionality.  

Cache-control headers include fields such as 'max-age' which defines the amount of time (in seconds) that will elapse before a new version or resource is requested by a user; ‘no-cache’ which forces clients to request new versions of resources every single time; and ‘must-revalidate’ which dictates that stale copies of content must be checked against their origin web server before being served.  

As such, cache-control headers allow developers to specify appropriate caching rules so that users have fast, up-to-date access to their data.  With this technology, REST API developers can ensure that their network performance is optimized for quality responses and peak performance. With effective cache control headers, applications can achieve optimal performance with minimal load on the host's resources.

When it comes to REST API, the amount of data sent in a POST method can vary depending on the application protocol and type of request. Generally speaking, there is no upper limit to the size of a payload as long as the receiving server is able to accommodate it. However, one should be mindful that an excessive payload size could affect page load times and other performance issues if they are not managed carefully. A good rule of thumb is to keep payloads under 10MB when possible.  

This is especially true for applications that need to exchange large amounts of data in a real-time environment. From client-side programming languages like JavaScript or Python, to backend frameworks like Laravel or NodeJS, all will come with certain maximum executable limits set by their respective developers – make sure you check this before sending very large payloads in order to avoid any unexpected errors or timeouts at runtime. Proper optimization techniques should also be employed when developing applications that will deal with large data sets or frequent POST requests.

Idempotency is an important property of some web service operations. An idempotent request is one that will always produce the same results, no matter how many times it is issued. This can be useful in two ways: it allows a client to make the same request more than once without having to worry about duplicate records in their data, and it also simplifies caching and replication for servers. In web services using the RESTful architecture, requests such as GET or PUT are typically treated as idempotent operations by design.  

To put it another way, if the same parameters are passed when making a request multiple times, the server should process each request as if it were unique rather than discarding any subsequent requests after the first one. This ensures consistency of data on both sides, reduces latency due to redundant requests, and can help improve performance overall. Furthermore, since these operations are designed with programmatic simplicity in mind, they can save time when compared to alternative non-idempotent methods such as POST or DELETE.

REST and AJAX are two popular tools used in designing user-friendly web applications. While they both come with various benefits, there are a few key differences between the two that any interviewer should be aware of. Fundamentally, REST stands for Representational State Transfer and is a set of rules and guidelines that developers can use to create consistent web services. It is primarily used to define how the server and client interact with each other over the internet.  

Alternatively, AJAX stands for Asynchronous JavaScript + XML and is an approach to updating content on web pages without having to reload the entire page. At its core, it utilizes HTTP requests which enable better control over what parts of the page are updated when content changes occur. Whereas REST relies on pre-defined structural guidelines, AJAX has more flexibility when it comes to making requests from servers or databases.

A REST API is a software protocol established by the World Wide Web Consortium that allows for the creation, consumption, and management of web-based services. A real-world example of a REST API is eBay’s corporate API platform, which developers can utilize to create web applications for both buyers and sellers. For instance, companies can use the API to create custom buyer interfaces that feature dynamic search results and personalized product recommendations.  

On the store side, developers can leverage the same API to build custom inventory tracking tools that give merchants enhanced insight into their data sets. What's more, eBay's user-friendly interface makes it easy for developers to integrate third party applications with the service while providing users with a seamless experience. All in all, eBay’s corporate API platform is a prime example of how real-world organizations can benefit from leveraging the power of REST APIs.

REST services are designed with scalability in mind, making them one of the best choices for applications that run on systems where high availability and maximum performance is needed. The key to a REST service's scalability lies in its uniform interface and how resource endpoints are managed and processed.  

Since every request goes through this interface, most of the heavy lifting can be done upfront; when requests come in, they go straight to the appropriate resource endpoint without needing complex parsing and validation, reducing processing time. Furthermore, any number of resource endpoints can be added without disrupting existing code since there is no hard-wired coding between resources.  

Finally, working with lightweight data formats like JSON or XML makes communication faster and easier while still allowing for adequate information exchange. Taken together, these features make using a REST API ideal for developing highly available and scalable web applications.

Caching is an important performance optimization technique for web applications. REST APIs can take advantage of caching in order to improve the performance of their applications. Caching allows a client to request data from a server without having to fetch it every time it needs it.  

This can be especially useful for resources that are accessed frequently, such as images or pieces of data that are used in multiple places within an application. When a client requests a resource that is cached, the server will return the cached version of the resource instead of fetching it from the database again.  

This can dramatically improve the performance of an application, since fetching data from a database can be a slow process. Caching can also reduce the load on a database, since it will not be accessed as often. There are many different caching strategies that can be used, and choosing the right one depends on the specific requirements of an application.

TLS, or transport layer security, is a protocol that helps to keep communication private and secure. TLS is often used in conjunction with HTTP, the protocol that powers the web. In recent years, there has been a push to use TLS with RESTful API design as well. While REST does not mandate the use of TLS, it is generally considered a best practice to implement it whenever possible.  

There are several benefits to using TLS with REST. First, it helps to ensure that data is not intercepted or tampered with during transit. Second, it provides a degree of authentication, helping to ensure that only authorized clients can access the API. Finally, it can help to improve performance by reducing the need for encryption at the application level. For these reasons, many experts recommend implementing TLS whenever possible when designing RESTful APIs.

A REST Resource is an object that represents a particular entity or item in a REST API. This can be anything from a single data item to a collection of data items. A Resource is typically identified by a unique URL, and can be accessed using the HTTP methods GET, POST, PUT, and DELETE. Each Resource has its own set of properties that describe the data it contains. For example, a User Resource might have properties such as name, email address, and date of birth. In addition to these data-oriented properties, a Resource also has a set of methods that define how it can be manipulated. 

For example, a User Resource might have methods for creating, updating, and deleting users. These methods are typically mapped to the HTTP methods POST, PUT, and DELETE respectively. Finally, a Resource also has a set of relations that define how it relates to other Resources in the API.  

For example, a User Resource might have a relation with a Group Resource which defines the groups that the user belongs to. relations are typically represented by URL templates which can be used to generate URLs for accessing related Resources.

There are a few different ways to design a web API, but one of the most popular architectures is known as REST, or Representational State Transfer. This style emphasizes simplicity and security, and it is often used for APIs that expose data or functionality to third-party developers. When designing a REST API, there are a few key principles to keep in mind.  

First, the API should be stateless, meaning that each request should stand on its own and not rely on any information from previous requests. Second, the API should be structured around resources, with each resource having its own unique URL. Finally, the API should use HTTP methods such as GET, POST, PUT, and DELETE to perform different actions on resources. By following these principles, you can create an API that is easy to use and scalable.

There are two main types of API architectures: SOAP and REST. SOAP (Simple Object Access Protocol) is a standards-based web services approach that uses XML for messaging. It relies on a collaborative partnership between the client and the server in order to function. REST (Representational State Transfer) is a more modern approach that uses simple HTTP requests to retrieve data.  

It is less complex and more lightweight than SOAP, making it a popular choice for web-based applications. When interviewing for a position that involves working with APIs, it is important to be familiar with both SOAP and REST. This will show that you understand the different approaches and can choose the best one for each situation.


When you build a REST API, you need to make sure that it is secure. Otherwise, anyone who knows the URL will be able to access your data. There are a few ways to secure a REST API:

  1. Use HTTPS: It ensures that all data passing between your server and clients is encrypted and difficult for third-parties to intercept.
  2. Authenticate Users: Make sure that only authenticated users can access your API. You can do this by requiring a user login or other form of authentication before allowing them to make any requests.
  3. Use Rate Limiting: Rate limiting helps to prevent abuse of your API by limiting the number of requests that can be made within a certain time period. It ensures that even if someone does manage to guess or brute force their way into your API, they won’t be able to make too many requests and cause damage.
  4. Input validation:  It is another important security measure that helps to ensure that the data being sent to your API is in the correct format and doesn’t contain any malicious code.
  5. Output encoding: It helps to prevent cross-site scripting (XSS) attacks by ensuring that the data being returned from your API is properly encoded and can’t be executed as code by the browser.

While creating a URI for your web service, there are some important best practices to keep in mind.

  • Keep it short and simple: Long and complicated URIs are hard to remember and can be error-prone. Where possible, use abbreviations and acronyms.
  • Be Consistent: Establishing a consistent URI structure makes it easier for developers to understand and use your web services. For example, if you're using a RESTful API, all URIs should follow a similar pattern.
  • Use Sensible Default Values: Whenever possible, provide default values for parameters in the URI. This reduces the necessary input from users and minimizes the chance of errors.
  • Version Your URIs: As your web services evolve over time, it's important to maintain backwards compatibility by versioning your URIs. This way, users can continue to access older versions of your API without having to make any changes to their code.

In addition, always use hyphens (-) instead of underscores (_) as word separators and do not include special characters such as #, $, &, +, ,, @, |, ^, etc. By following these best practices you can create user-friendly URIs that are easily accessible and easy to use.

It's no surprise that this one pops up often in REST API interview questions for experienced.

The key difference between SOAP and REST is that SOAP is a protocol, while REST is an architectural style. In other words, SOAP defines how two systems should communicate with each other, while REST provides guidelines for how web services should be designed.

There are a few key factors that you need to consider when deciding whether to use SOAP or REST for your web services. These include:

  1. The nature of the data being exchanged: SOAP is better suited for exchanging structured data, while REST is more efficient for exchanging unstructured data.
  2. Level of security required: SOAP services can take advantage of features like WS-Security, while REST services typically rely on HTTPS for security, so if security is a key concern, then SOAP may be the better option.
  3. Level of integration required: SOAP web services can be more easily integrated with other systems than RESTful web services.  
  4. Needs of the client: If the client needs to access only specific data, then REST may be the better option, but if the client needs to access all data, then SOAP may be more suitable. Moreover, REST services are generally faster and use less bandwidth than SOAP services.  
  5. Level of functionality required: SOAP web services tend to offer more functionality than RESTful web services.

Monolithic architectures are defined as a single unit where all components are tightly coupled and share the same database. In a monolithic architecture, if one component needs to be updated, the entire system must be redeployed. Monolithic architectures are typically built using the waterfall model.

SOA (service-oriented architecture) is an architecture where components are independent and communicate with each other through web services. In a SOA architecture, each component can be updated independently without affecting the other components. SOA architectures are typically built using an iterative or agile methodology.

Microservices architectures are defined as a set of small, independently deployable services. In a microservices architecture, each service has its own database and can be updated independently. Microservices architectures are typically built using an iterative or agile methodology.

There are a number of directives that can be included as part of the Cache-Control header in an HTTP response. The "public" directive indicates that the resource is cacheable by any component. This is in contrast to the "private" directive, which indicates that the resource can only be cached by the client, and not by any intermediate proxies.  

The "no-cache" directive indicates that the resource maybe cached by the browser but after submitting validation requires to origin server, and the "no-store" directive indicates that the resource should not be stored on disk. In addition, the "must-revalidate" directive indicates that cached copies of the resource must be revalidated with the server before use, and the "proxy-revalidate" directive indicates that cached copies of the resource must be revalidated with the server before use by any proxy.

This is a frequently asked question in REST API advanced interview questions.

Usage limits are important in REST APIs because they help ensure that the API can continue functioning properly even when it is under heavy use. There are two main types of usage limits: rate limits and concurrent request limits. Rate limits restrict the number of requests that can be made to the API in a given period of time, while concurrent request limits restrict the number of requests that can be processed simultaneously.  

Both types of limits help prevent API overuse, which can lead to degraded performance or even downtime. When setting usage limits, it is important to strike a balance between ensuring adequate availability for legitimate users and preventing abuse by malicious actors.

In RESTful web services, addressing is the process of specifying the location of a resource that is being requested. This is done by including the resource's identifier in the URL. For example, if a user wants to retrieve a list of all the products offered by a particular store, they would send a GET request to the /products endpoint.  

The server would then return a list of all the products available at that store. If a user wanted to retrieve a specific product, they would include the product's identifier in the URL. For example, if a user wanted to retrieve information about product #12345, they would send a GET request to the /products/12345 endpoint. The server would then return information about that product. Addressing is an important part of RESTful web services because it allows users to access resources without having to know the underlying structure of the data.

The Accept and Content-Type headers are used to indicate what kind of content the client is expecting to receive, or what kind of content the server is sending. For example, if a client sends an Accept header of "text/plain", it is indicating that it only wants to receive plain text content.  

Conversely, if a server sends a Content-Type header of "text/plain", it is indicating that the content it is sending is plain text. These headers are important because they help to ensure that the client and server are both on the same page with regards to the type of content being exchanged. Without these headers, it would be very easy for confusion to arise, and for the wrong type of content to be sent or received.

API testing generally refers to the process of testing an application programming interface to determine if it meets expectations for functionality, performance, reliability, and security. Unit testing, on the other hand, is a type of software testing that covers individual units of source code to determine if they are fit for use.  

API testing is often performed at the API level, which is higher up in the software development process than unit testing. As a result, API tests tend to be more comprehensive and can catch errors that unit tests might miss. API tests also tend to be more expensive and time-consuming to set up and maintain than unit tests.  

Despite these differences, API testing and unit testing share some common goals, such as ensuring that software meets business requirements and is free of defects. Both types of testing also rely on similar technical approaches, such as automated testing and test-driven development. Ultimately, the decision of whether to use API testing or unit testing (or both) depends on the specific needs of the project being developed.

The purpose of the HEAD method is to retrieve metadata about the resource without returning the actual resource itself. This can be useful for checks to see if a resource has been updated without having to retrieve the entire resource. For example, if a client cached an image and wants to check if it has been updated, it can make a HEAD request instead of a GET request. If the image has been updated, the server will return a new Last-Modified header.  

The client can then roundtrip the new Last-Modified value back to the server using an If-Modified-Since header on a subsequent GET request. This allows the server to avoid retrieving and sending unnecessary data. In general, HEAD requests should have the same semantics as GET requests, but with no response body. That is, a HEAD request should not change the state of the server or have any side effects.

JAX-RS stands for Java API for RESTful Web Services. It is a set of standards that are used for creating web services. JAX-RS can be implemented in various frameworks such as Jersey, Apache CXF, and RESTEasy. Each of these frameworks has its own set of features and characteristics.  

For example, Jersey is a Java-based framework that is built on top of the JAX-RS standards. It provides support for various features such as HTTP caching, content negotiation, and SSL security. Apache CXF is another popular framework that can be used for developing RESTful web services. It supports a wide range of features such as WS-Security, failover, and load balancing.  

Lastly, RESTEasy is a JBoss project that provides an easy-to-use framework for developing RESTful web services. It supports various features such as JSON processing, XML binding, and asynchronous request processing.

RESTEasy is a JBoss project that provides various frameworks to help you build RESTful Web Services and RESTful Java applications. It is a fully certified and portable implementation of the JAX-RS specification. RESTEasy can run in any Servlet container, but it really shines when used on JBoss AS, WildFly, and Keycloak.  

RESTEasy also provides an enhanced bootstrap process that allows you to deploy WAR files that contain JAX-RS annotated classes directly into your servlet container. You can also embed a Jersey container within your application. This allows you to deploy WAR files with jersey annotated classes directly into your servlet container. RESTEasy also has support for CDI(Context and Dependency Injection) 1.1+ and @Inject annotations can be used throughout your application to grab references to CDI beans.  

You can also use @ObservesAsync to observe CDI events asynchronously. When used with JBoss Weld, you can even get EJB dependency injection outside the EE environment by just adding a beans.xml file to your application classpath! Finally, if you are using Jackson for your JSON processing then you will be happy to know that RESTEasy integrates very well with it and provides an easy way for you to configure how your JSON is processed.

A staple in REST API interview questions and answers, be prepared to answer this one.

When it comes to web services, security is always a top concern. After all, web services are responsible for handling sensitive data, and any security breach could have serious consequences.  

There are a number of different security issues that web services need to be aware of, but some of the most common include Cross-Site Request Forgery (CSRF), SQL injection, and cross-site scripting (XSS). CSRF attacks exploit the fact that web browsers automatically send cookies with requests to the server, even if the user didn't intend to make a request. This can allow an attacker to inject illegitimate requests that are executed by the server without the user's knowledge.  

SQL injection occurs when an attacker is able to insert malicious code into a SQL query, which is then executed by the server. This can allow the attacker to gain access to sensitive data or even take control of the entire website. XSS attacks occur when an attacker is able to insert malicious code into a web page, which is then executed by the user's browser.  

This can allow the attacker to steal sensitive information or redirect the user to a malicious website. By being aware of these security risks, web services can take steps to protect themselves and their users.

Microservice architecture is an approach to designing large, complex applications as a collection of small, independent services. Each service has a well-defined purpose and is self-contained, making it easy to develop, deploy, and scale. This modular approach allows for greater flexibility and easier maintenance, as new features can be added or removed without affecting the rest of the system. microservices can be deployed on various servers, making it possible to scale specific parts of the application as needed.  

This can result in significant cost savings, as you only need to pay for the resources you actually use. In addition, microservices can be implemented in different programming languages, making it easier to find developers with the necessary expertise. Ultimately, microservice architecture provides a more efficient and scalable way to build large-scale applications.

CRUD is an acronym for "create, read, update, and delete." CRUD operations are the basic functions of persistent storage. Creating data means inserting data into the database. Reading data means selecting data from the database. Updating data means updating existing data in the database. Deleting data means deleting data from the database.  

Although CRUD is often used in the context of databases, it can also refer to the basic functions of any storage system, such as a file system. Most storage systems support at least some of the CRUD operations. For example, a file system supports creating and deleting files, and it may also support reading and writing files.  

Databases typically provide more powerful ways to manipulate data than file systems, such as SQL queries. However, both file systems and databases support the most basic form of CRUD: creating new files or records.

One of the key constraints of a uniform interface is that it must be stateless. This means that each request from a client must contain all of the information necessary for the server to fulfill the request. The server cannot rely on any state information that might have been stored from previous requests.  

In addition, the uniform interface must be independent of the underlying implementation. This means that clients should not be able to make assumptions about how the server is implemented. For example, they should not be able to assume that data is stored in a relational database.  

Finally, the uniform interface must be self-descriptive. This means that each message sent between client and server must contain enough information for the recipient to understand it. For example, messages must include an indication of which resources are being accessed and what actions are being performed on those resources. By adhering to these constraints, RESTful APIs can provide a clean and consistent interface that is easy to use and understand.

The header of the HTTP response that provides the date and time of the resource when it was created is the Last-Modified header. This header contains the date and time of the last modification made to the resource. The date and time are represented in Greenwich Mean Time (GMT).  

The Last-Modified header is used to determine whether a cache entry is fresh or stale. A cache entry is fresh if the cache entry's age is less than or equal to the max-age value of the Cache-Control header. A cache entry is stale if its age is greater than the max-age value of the Cache-Control header.

There are many elements to check when testing an API. One of the most important is performance. This includes testing how quickly the API responds to requests, as well as how efficiently it uses bandwidth and other resources. Another key element is correctness. This means ensuring that the API returns the correct data for the given input, and that it behaves correctly in edge cases.  

Also, it is important to test for security vulnerabilities, such as SQL injection attacks. Finally, it is also important to test for usability issues, such as whether the API is easy to use and understand.

A Web API is a platform for building web applications that can be accessed over the Internet. It provides a way for client-side applications to communicate with server-side applications, making it possible to develop cross-platform applications. There are many different types of Web APIs, but some common examples include databases, payment processors, and social media platforms.  

In order to use a Web API, developers need to first register with the provider and obtain an API key. This key is used to authenticate requests made to the API. Once registered, developers can use the API to access data or perform actions on behalf of the user.  

For example, a developer could use the Twitter API to display a user's timeline on their website. Alternatively, they could use the Stripe API to process payments made through their online store. By using Web APIs, developers can easily add powerful functionality to their applications without having to build everything from scratch.

The @RequestMapping annotation is used to map web requests to Spring MVC controllers. It can be placed on a class or on methods in a controller. When placed on a class, all controller methods are mapped. When placed on a method, only that specific method is mapped. The @RequestMapping annotation supports a variety of attributes, such as headers, params, consumes, produces, and more. These attributes can be used to narrow the mapping so that it only applies to specific requests.  

For example, the params attribute can be used to specify the request parameters that must be present for the mapping to apply. The @RequestMapping annotation can also be used to specify the request method (GET, POST, etc.) and the media type (text/html, application/json, etc.) that the mapped controller method can handle.

The proper representation of resources is required in order to provide an accurate and up-to-date picture of the state of the resources. REST API interviewers often ask this question in order to gauge a candidate's understanding of how REST APIs work. In order to properly represent a resource, an application needs to retrieve the latest data from the resource, and then convert that data into a format that can be consumed by the client.  

This process can be complex, and requires a deep understanding of both the resource and the client. Without proper representation, a resource can quickly become outdated, and this can lead to errors or unexpected behavior from the client.  

Therefore, it is essential that applications take care not only to retrieve the latest data from resources, but also to represent that data in a way that is both accurate and easy for the client to consume.

When talking about the client-server constraint of REST APIs, we are referring to the separation of concerns that is inherent in the architecture. The client is responsible for the user interface, while the server is responsible for storing and retrieving data. This separation of concerns allows for a more modular approach to development, and it also makes it easier to scale an application.  

When an application grows too large for a single server to handle, it can be divided up into multiple smaller services, each running on its own server. This horizontally scalable architecture is one of the key benefits of using a REST API.

Yes, it is possible to use Restlet without a web container. While Restlet is often used in conjunction with web containers for efficiency and greater compatibility with web-based applications, it is not required. Restlet can run stand-alone or in any Java environment. This makes it ideal for use in both desktop and server-side applications.  

Moreover, Restlet offers a number of features that are not typically found in web containers, such as support for content negotiation and automatic generation of documentation. As a result, using Restlet does not necessarily require using a web container.

When considering the creation of web services, one must decide between two distinct approaches: the top-down and bottom-up models. The former begins with a general view of the project, dividing its broad aspects into components; this is usually followed by a review of each component in detail. The latter approach plans from the detailed components up to the broader system as a whole. Both methods have their own set of strengths and weaknesses as far as REST API development is concerned.  

The bottom-up approach is useful when dealing with an existing architecture, as it helps to address individual components without disturbance or alteration to other parts. On the other hand, top-down development provides an initial plan that includes the full scope of what’s needed to achieve success. It also helps create smaller projects that developers can work on simultaneously instead of carrying out separate tasks sequentially.  

Ultimately, which approach you choose will depend upon your unique requirements and budget limitations as well as time restraints; depending upon these specific needs, one strategy may be more advantageous than another. In any case, understanding both options allows you to make an informed decision regarding REST API development.

The GET method is one of the most common and important commands used in REST (Representational State Transfer). As the name suggests, the GET method is used to retrieve data from an API endpoint. When you make a call to a server using the GET method, it communicates with the host, sends a request for the specific piece of data you asked for, then receives that information as a response.  

The syntax of a GET request resembles a URL address; specifically, it's made up of three components: The resource path which defines what should be retrieved; options which are used to modify how the requested resource should be treated; and parameters which contain metadata providing additional information about the request. It's important to note that because the GET method retrieves data, it doesn't cause any changes to server-side resources or modify any other parts of your application.  

For these tasks, you must use other REST methods such as POST or PUT. Additionally, while authentication isn't required when making a valid GET request, certain requests may require some type of authorization before they can be successfully delivered. With that said, understanding how to use and apply the GET method is essential for anyone looking to answer questions about REST APIs in an interview and showcase their proficiency in this area.


REST is an architectural style for building web services. It is based on a few key principles, including the use of HTTP methods to perform CRUD operations (create, read, update, delete) and the use of HTTP status codes to indicate the success or failure of those operations. REST also makes use of resources, which URIs identify. These resources can be manipulated using the HTTP methods, and the results of those manipulations are returned in JSON or XML format. Finally, RESTful web services are stateless, meaning each request is independent of any other request. This makes them easy to scale and maintain.

You're in luck if you're looking for a job that involves working with APIs. API jobs are rising, and the demand for API developers far exceeds the supply. As of now, the number of API-related job postings has increased over the past years. With so much demand and few qualified candidates, now is the time to brush up on your API skills from Flask API, Advanced REST client, to Python REST API.  

To help you prepare for your next REST API interview, we've compiled a list of REST API interview questions for experienced & beginners. We'll cover everything from an API and how it works to designing and testing APIs. Moreover, you can boost your skill set with enrollment in a REST API course. This will help you get full developer experience quickly and increase your confidence in your interview.  

By the end, you'll have all the necessary knowledge to ace your next API interview. To get the best out of yourself, you can even opt for the programming courses that will improve your understanding with the assistance of top-notch industry experts. If you know how to answer these sorts of REST API interview questions with our guidance, you'll be on your way to impressing potential employers and landing the full-stack developer job you've always wanted.

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