REST API

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.