RESTful web services Interview Questions

What is a RESTful web service?

A RESTful web service is a web service that follows the principles of the Representational State Transfer (REST) architectural style. It is designed to be stateless, client-server, cacheable, and have a uniform interface. RESTful web services use HTTP methods such as GET, POST, PUT, and DELETE to perform CRUD (Create, Read, Update, Delete) operations on resources.

How does Spring Boot simplify the development of RESTful web services?

Spring Boot simplifies the development of RESTful web services by providing a set of pre-configured components and annotations that make it easy to set up and configure a RESTful web service. For example, Spring Boot provides annotations such as @RestController and @RequestMapping to define REST endpoints, and it includes an embedded Tomcat or Jetty server to make it easy to deploy and run the application.

What is the difference between @RestController and @Controller in Spring Boot?

@RestController is a specialized version of the @Controller annotation in Spring Boot that is used to define RESTful web services. The main difference is that @RestController combines @Controller and @ResponseBody, which eliminates the need to annotate every request mapping method with @ResponseBody.

What is the role of the @RequestMapping annotation in Spring Boot?

The @RequestMapping annotation is used to map a URL pattern to a controller method in Spring Boot. It defines the HTTP method (GET, POST, PUT, DELETE, etc.) and the URL pattern that should trigger the execution of the annotated method.

How does Spring Boot handle content negotiation in RESTful web services?

Spring Boot provides content negotiation support in RESTful web services by using the ContentNegotiationConfigurer class. This class allows you to configure content negotiation based on the Accept header in the HTTP request. Spring Boot also provides message converters that convert objects to and from JSON, XML, and other formats, based on the media type specified in the Accept header.

How does Spring Boot handle error handling in RESTful web services?

Spring Boot provides a set of default error-handling mechanisms for RESTful web services. These include using HTTP status codes to indicate errors, returning error messages in the response body, and using exception handling to handle errors that occur during request processing. Spring Boot also provides a @ControllerAdvice annotation that can be used to define global exception-handling logic for an application.

What is Swagger in Spring Boot, and how is it used?

Swagger is a popular tool for documenting RESTful web services in Spring Boot. It allows you to define the API endpoints, request parameters, and response formats for a web service in a machine-readable format. This documentation can then be used to generate client libraries and interactive API documentation. In Spring Boot, Swagger can be integrated using the springfox-swagger2 and springfox-swagger-ui dependencies, along with annotations such as @Api, @ApiOperation, and @ApiModel.

What are the features of RESTful Web Services?

The features of RESTful web services include:

1. Resource identification through URI: Resources in a RESTful web service are identified using a unique URI (Uniform Resource Identifier). The URI is used to locate and manipulate the resource.
2. Use of HTTP methods: RESTful web services use HTTP methods (GET, POST, PUT, DELETE) to perform operations on resources. These methods are mapped to CRUD (Create, Read, Update, Delete) operations.
3. Representations: Resources in a RESTful web service can be represented in different formats such as XML, JSON, HTML, and plain text. The client can request the representation of the resource that it needs.
4. Stateless: RESTful web services are stateless. This means that the server does not store any client context between requests. Each request is treated as a new request.
5. Cacheable: Responses from RESTful web services can be cached on the client side or on the server side. This can improve performance and reduce network traffic.
6. Layered system: RESTful web services can be designed as a layered system with different layers responsible for different functions. This can make the system more scalable and flexible.
7. Uniform interface: RESTful web services use a uniform interface between clients and servers. This interface is made up of a set of standard methods and protocols that are shared by all resources in the system.
8. Self-descriptive messages: Messages in a RESTful web service are self-descriptive. This means that each message contains all the information necessary to process the request, including metadata about the resource being requested.

What do you understand by JAX-RS?

JAX-RS stands for Java API for RESTful Web Services. It is a Java programming language API that provides support for building RESTful web services. JAX-RS was developed as part of the Java EE (Enterprise Edition) platform and is now included in Java SE (Standard Edition).

JAX-RS provides a set of annotations and APIs that developers can use to build RESTful web services. The annotations are used to map Java methods to HTTP requests and specify the HTTP method (GET, POST, PUT, DELETE) and URL path. The APIs are used to handle incoming HTTP requests and produce the appropriate response.

JAX-RS supports different types of data representation such as JSON, XML, and plain text. It also supports content negotiation, which allows clients to request the representation of a resource that best suits their needs.

JAX-RS is widely used in Java-based web development and is a popular choice for building RESTful web services due to its simplicity, flexibility, and portability.

What is URI in RESTful web services?

URI stands for Uniform Resource Identifier. In RESTful web services, a URI is a string of characters that identifies a resource.

The URI is used to locate and manipulate the resource in a RESTful web service. It typically consists of a domain name, followed by a path that identifies the resource. For example, in the URI “https://example.com/api/customers/123”, “https://example.com” is the domain name and “/api/customers/123” is the path that identifies the resource.

In RESTful web services, URIs are designed to be human-readable and easily understandable. They should be consistent and predictable so that clients can easily locate and interact with resources.

URIs are an important part of the RESTful architecture, as they provide a way for clients to access and manipulate resources using standard HTTP methods (GET, POST, PUT, DELETE). By using a URI, clients can make requests to a server and receive a response that represents the state of the requested resource.

What is the concept of statelessness in REST?

Statelessness is a key concept in RESTful web services. It means that the server does not maintain any information about the client between requests. Each request is treated as a new and independent request.

In other words, the server does not store any client context or session information. This allows the server to be more scalable and reduces the complexity of the system.

When a client makes a request to a RESTful web service, it must include all the information necessary for the server to process the request. This includes any authentication or authorization credentials, as well as any data required to complete the request.

The server then processes the request and sends back a response that represents the state of the requested resource. The response may include links or other information that the client can use to perform further operations on the resource.

Statelessness is a fundamental principle of RESTful web services and helps to ensure that the system is scalable, flexible, and maintainable. It also makes it easier to test and debug the system, as each request can be treated as a standalone unit.

What are the HTTP Methods?

RESTful web services use standard HTTP methods (also called verbs) to perform operations on resources. These methods are mapped to CRUD (Create, Read, Update, Delete) operations. The HTTP methods used in RESTful web services are:

1. GET: Used to retrieve a resource from the server. It should not modify any data on the server.
2. POST: Used to create a new resource on the server. It can also be used to submit data to the server.
3. PUT: Used to update an existing resource on the server. It replaces the existing resource with new data.
4. DELETE: Used to delete a resource from the server.
5. PATCH: Used to update part of an existing resource on the server.
6. OPTIONS: Used to retrieve information about the communication options available for a resource.
7. HEAD: Similar to the GET method, it only retrieves the header information for a resource.

These HTTP methods provide a standard way to perform operations on resources in a RESTful web service. By mapping each HTTP method to a specific CRUD operation, clients can interact with the server in a consistent and predictable way. This helps to ensure that the system is scalable, flexible, and maintainable.

What are Idempotent methods?

In RESTful web services, an idempotent method is a method that can be applied multiple times without changing the result beyond the initial application. In other words, an idempotent method will produce the same result, regardless of the number of times it is applied.

Idempotent methods are important in RESTful web services because they allow clients to safely retry a failed request without causing any unintended changes to the state of the resource on the server. This is especially important in distributed systems where network failures can occur.

The following HTTP methods are considered idempotent:

1. GET: Retrieving a resource multiple times will not change the state of the resource on the server.
2. PUT: Updating a resource with the same data multiple times will not change the state of the resource on the server beyond the initial update.
3. DELETE: Deleting a resource multiple times will not change the state of the resource on the server beyond the initial deletion.

It’s worth noting that the POST method is not idempotent. Submitting the same data multiple times using POST will result in multiple resources being created on the server.

In summary, idempotent methods in RESTful web services are methods that can be safely applied multiple times without changing the result beyond the initial application. They are important for ensuring consistency and reliability in distributed systems.

Can you tell me the disadvantages of RESTful web services?

Although RESTful web services have many advantages, they also have some disadvantages, including:

1. Lack of standardization: While the RESTful architecture is widely used, there is no standardization for how RESTful web services should be designed or implemented. This can lead to inconsistencies in how resources are exposed and how operations are performed.
2. Lack of strong typing: RESTful web services typically use JSON or XML for data representation, which does not enforce strong typing. This can lead to issues with data validation and error handling.
3. Limited functionality: While RESTful web services are great for simple CRUD operations, they may not be the best choice for more complex business logic or transactions.
4. Security concerns: RESTful web services are vulnerable to security issues such as SQL injection, cross-site scripting, and CSRF attacks. Careful consideration and implementation of security measures are required to mitigate these risks.
5. Performance overhead: RESTful web services typically involve more network overhead than other architectures, such as binary protocols like gRPC. This can lead to slower performance, especially over high-latency or low-bandwidth networks.
6. Caching challenges: Because RESTful web services are stateless, caching can be a challenge. Caching can improve performance, but it must be done carefully to avoid stale data and consistency issues.

While RESTful web services have become very popular due to their simplicity and scalability, they may not be the best choice for every use case. It is important to consider the specific needs of the application when deciding on an architecture.

Differentiate between SOAP and REST?

SOAP and REST are two popular web service architectures used for exchanging data between different applications. The main differences between SOAP and REST are:

1. Protocol: SOAP (Simple Object Access Protocol) is a protocol whereas REST (Representational State Transfer) is an architectural style.
2. Data format: SOAP typically uses XML for data representation, while REST uses a variety of data formats including JSON and XML.
3. HTTP methods: RESTful web services use standard HTTP methods (GET, POST, PUT, DELETE) to perform operations on resources, whereas SOAP uses a single POST method with a SOAP payload.
4. Flexibility: RESTful web services are flexible and can be used with any programming language, whereas SOAP is typically used with Java or .NET.
5. Complexity: SOAP is typically more complex than REST, with more overhead due to the use of XML and the SOAP envelope. This can result in slower performance and higher resource usage.
6. Caching: RESTful web services can leverage caching to improve performance, while caching is not typically used with SOAP.
7. State management: RESTful web services are stateless, meaning that each request is independent and does not rely on previous requests. SOAP, on the other hand, can maintain state between requests.

In summary, while SOAP and REST both have advantages and disadvantages, REST has become the more popular choice for modern web services due to its simplicity, flexibility, and ability to leverage standard HTTP methods.

What are the differences between PUT and POST in REST?

In RESTful web services, PUT and POST are both used to update resources on the server, but they have different semantics and should be used in different scenarios:

1. PUT: PUT is used to update an existing resource or create a new resource with a known URI. If a resource with the specified URI already exists, the resource is updated with the new data. If the resource does not exist, a new resource is created with the specified URI. PUT is idempotent, meaning that sending the same request multiple times will result in the same resource state on the server.
2. POST: POST is used to submit new data to the server to create a new resource when the server decides the URI of the new resource. POST is not idempotent, meaning that sending the same request multiple times may result in multiple resources being created on the server. POST is commonly used for operations that change the state of the server, such as submitting a new order or creating a new user account.

In summary, PUT is used to update or create a resource with a known URI, while POST is used to create a new resource when the server decides the URI of the new resource. PUT is idempotent, while POST is not.

What is Payload in terms of RESTful web services?

In RESTful web services, the payload refers to the data being transmitted in a request or response. This data can be in different formats, such as JSON, XML, or plain text. The payload typically contains the actual data being exchanged between the client and server, such as the parameters of a request or the response data from a server.

For example, when a client sends a POST request to create a new resource, the payload contains the data that defines the new resource. Similarly, when a client sends a GET request to retrieve a resource, the payload contains the data that represents the requested resource.

In general, the payload is an important component of a RESTful web service because it contains the actual data being exchanged between the client and server. The format of the payload can be negotiated between the client and server using HTTP headers, allowing for flexibility in data exchange.

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

In theory, there is no specific maximum payload size that can be sent in a POST method in RESTful web services. The HTTP/1.1 specification does not define any specific limits on payload size, but servers or network infrastructure may impose their own limits.

However, in practice, there are some factors that can limit the payload size, such as the maximum size allowed by the server, network bandwidth, and the processing power of the client and server. Many web servers have a limit on the maximum payload size that can be sent in a POST request, typically ranging from a few megabytes to several gigabytes. Additionally, some web clients may have their own limitations on the maximum payload size they can send.

It is generally recommended to use smaller payloads whenever possible to improve performance and reduce the risk of network errors or timeouts. If larger payloads are required, it is important to ensure that the server and network infrastructure can handle the increased traffic, and to consider using techniques such as chunked encoding or compression to optimize the data transfer.

Is it possible to send the payload in the GET and DELETE methods?

In theory, it is possible to send payload in the GET and DELETE methods in RESTful web services, but it is generally not recommended or considered best practice.

According to the HTTP/1.1 specification, the GET and DELETE methods are intended for safe and idempotent operations, respectively. The GET method is used to retrieve a resource from the server, and the DELETE method is used to delete a resource from the server. Since these methods are not designed for sending data, most web servers and clients do not support sending a payload in a GET or DELETE request.

While some web frameworks may allow sending payload in GET and DELETE requests, it is generally considered bad practice because it can be difficult to manage, and may cause security or compatibility issues. Instead, it is recommended to use other methods such as POST or PUT to send data to the server, and to use GET and DELETE methods only for their intended purposes of retrieving or deleting resources.

How does HTTP Basic Authentication work?

HTTP Basic Authentication is a simple authentication mechanism used by web applications to authenticate users. In this mechanism, the user’s credentials are encoded and sent in the HTTP headers of a request. Here’s how it works:

1. When a user tries to access a protected resource on a server, the server responds with a 401 Unauthorized status code and a WWW-Authenticate header that contains the authentication scheme.
2. The client then resends the request with the user’s credentials encoded in the Authorization header. The Authorization header consists of the authentication scheme, followed by the user’s credentials, which are encoded as a base64 string.
3. The server decodes the base64 string and verifies the user’s credentials against a user database or authentication provider. If the credentials are valid, the server grants access to the protected resource and sends a response with a 200 OK status code. Otherwise, the server responds with a 401 Unauthorized status code.

HTTP Basic Authentication is simple to implement, but it has several limitations. Firstly, the credentials are sent in plain text, making it vulnerable to interception by attackers. Secondly, it does not support logout or session management, making it difficult to revoke access once the user has been authenticated. Finally, it does not provide any mechanism for additional security features such as encryption, two-factor authentication, or access control lists.

What is RestTemplate in Spring/Spring Boot?

RestTemplate is a class provided by Spring and Spring Boot frameworks that simplifies the process of making HTTP requests to RESTful web services. It is a synchronous client-side HTTP communication library that simplifies the interaction with HTTP servers and enforces RESTful principles.

RestTemplate provides a high-level API for making HTTP requests, handling responses, and converting data between different formats, such as JSON or XML. It supports all the standard HTTP methods (GET, POST, PUT, DELETE, etc.) and provides a variety of options for configuring the request, such as adding headers, setting timeouts, and specifying the request body.

RestTemplate can also be easily extended and customized through the use of interceptors and message converters, making it highly flexible and adaptable to different use cases.

In summary, RestTemplate is a powerful and flexible tool for consuming RESTful web services in Spring and Spring Boot applications, and can greatly simplify the process of interacting with remote APIs.

Difference between @PathVariable and @RequestParam annotations in RESTful Web Services.

In RESTful Web Services, @PathVariable and @RequestParam are two annotations that are used to extract data from the URL of a request. However, they are used for different purposes and have some key differences.

@PathVariable: This annotation is used to extract data from the path portion of the URL. It is used to bind a path variable, which is a placeholder in the URL, to a method parameter. For example, in the URL “/books/123”, “123” is a path variable that can be extracted using @PathVariable. An example usage of @PathVariable in Spring Boot would be:

@GetMapping(“/books/{id}”)

public Book getBook(@PathVariable Long id) {

    // …

}

@RequestParam: This annotation is used to extract data from the query string portion of the URL. It is used to bind a request parameter to a method parameter. For example, in the URL “/books?id=123”, “123” is a query parameter that can be extracted using @RequestParam. An example usage of @RequestParam in Spring Boot would be:

@GetMapping(“/books”)

public Book getBook(@RequestParam Long id) {

    // …

}

The main difference between @PathVariable and @RequestParam is that @PathVariable extracts data from the path portion of the URL, while @RequestParam extracts data from the query string portion of the URL. Additionally, @PathVariable is typically used to extract information about a resource (e.g., the ID of a book), while @RequestParam is typically used to filter or sort a list of resources (e.g., to retrieve all books by a certain author).

Is it necessary to keep Spring MVC in the classpath for developing RESTful web services?

Yes, it is necessary to keep Spring MVC in the classpath for developing RESTful web services using Spring Framework. This is because Spring MVC provides the necessary infrastructure for handling HTTP requests and responses, which is essential for building RESTful web services.

Spring MVC is a web framework that provides a Model-View-Controller (MVC) architecture for building web applications. It includes a number of components that are specifically designed for handling web requests and responses, such as controllers, request handlers, and view resolvers. It also provides support for handling different types of content, such as HTML, JSON, and XML.

In Spring Framework, RESTful web services are typically built using the Spring MVC framework, which provides a number of annotations and components that make it easy to create RESTful APIs. For example, the @RestController annotation can be used to create a controller that handles RESTful requests and returns data in JSON format.

So, in summary, keeping Spring MVC in the classpath is essential for developing RESTful web services using Spring Framework.

While creating URI for web services, what are the best practices that need to be followed?

Here are some best practices that should be followed while creating URIs for web services:

1. Use nouns instead of verbs: A URI should represent a resource or a collection of resources, not an action. Therefore, it is recommended to use nouns instead of verbs in URIs.
2. Use lowercase letters: URIs are case-sensitive, so it is recommended to use lowercase letters to avoid confusion and errors.
3. Use hyphens or underscores to separate words: To make URIs more readable, it is recommended to use hyphens or underscores to separate words.
4. Use plural nouns for collections: For collections of resources, it is recommended to use plural nouns in the URI. For example, /books instead of /book.
5. Use specific resource names: Use specific resource names instead of generic ones. For example, instead of using /items, use /books, /movies, /products, etc.
6. Use query parameters for filtering or sorting: Use query parameters to filter or sort a collection of resources. For example, /books?author=Stephen+King&orderBy=publishedDate.
7. Avoid using query parameters for resource identification: Avoid using query parameters to identify resources. Instead, use path parameters or matrix parameters.
8. Use versioning: If you need to make changes to your API, it is recommended to use versioning in your URIs to avoid breaking existing clients. For example, /v1/books, /v2/books, etc.

By following these best practices, you can create URIs that are easy to read, understand, and maintain.

What makes REST services to be easily scalable?

RESTful web services are designed to be easily scalable due to the following reasons:

1. Stateless: RESTful web services are stateless, which means that each request contains all the necessary information to complete the request. This makes it easier to distribute the requests across multiple servers without having to worry about session management or server affinity.
2. Caching: RESTful web services support caching, which allows the clients to cache the responses and reduces the number of requests made to the server. This improves the performance of the application and reduces the load on the server.
3. Uniform interface: RESTful web services have a uniform interface, which makes it easier to add new resources or modify existing ones without affecting the clients. This makes it easier to evolve the API and add new features without breaking existing clients.
4. Lightweight: RESTful web services are lightweight and use standard HTTP protocols, which makes it easier to handle large numbers of requests and responses. This makes it easier to scale the application horizontally by adding more servers to handle the load.
5. Separation of concerns: RESTful web services separate the concerns of the server and the client, which makes it easier to develop and maintain the application. This also makes it easier to scale the application by adding more servers to handle the load.

By following these principles, RESTful web services can be easily scaled horizontally by adding more servers to handle the load. This allows the application to handle large amounts of traffic and provide a high level of availability and reliability.

Based on all factors, you can decide which type of web services you need to use – SOAP or REST?

The choice between SOAP and REST depends on several factors such as:

1. Complexity: If the application is complex and requires a high level of reliability and security, SOAP may be a better choice as it has built-in standards for error handling, security, and reliable messaging.
2. Performance: If the application requires high performance and low latency, REST may be a better choice as it is lightweight and uses standard HTTP protocols.
3. Integration: If the application needs to integrate with existing systems that use SOAP, it may be easier to use SOAP as it has built-in support for WSDL and XML.
4. Flexibility: If the application needs to evolve and change frequently, REST may be a better choice as it has a more flexible architecture and can handle changes more easily.
5. Resources: If the application has limited resources and needs to run on low-power devices, REST may be a better choice as it has a lightweight architecture that requires fewer resources.
6. Community: The availability of community resources, tools, and support can also influence the choice between SOAP and REST.

Therefore, it is important to consider these factors before deciding which type of web service to use in a particular scenario. Ultimately, the decision should be based on the specific requirements of the application and the constraints of the environment in which it will be deployed.

How can you test RESTful Web Services?

There are various ways to test RESTful web services:

1. Manual testing: Manual testing involves using tools like Postman, RESTClient, or curl to test the RESTful web services by sending HTTP requests and verifying the responses.
2. Automated testing: Automated testing involves using testing frameworks like JUnit or TestNG to write test cases for RESTful web services. These test cases can be run automatically to verify the functionality of the web services.
3. Integration testing: Integration testing involves testing the RESTful web services in conjunction with the other components of the application, such as the database, message queues, or other external systems.
4. Load testing: Load testing involves testing the performance of RESTful web services under heavy loads to ensure that they can handle a large number of requests without degrading performance.
5. Security testing: Security testing involves testing the RESTful web services for vulnerabilities such as injection attacks, cross-site scripting (XSS), and cross-site request forgery (CSRF).

Overall, testing RESTful web services involves verifying that they adhere to the REST architectural constraints, handle HTTP requests and responses properly, and provide the expected functionality in a secure and scalable manner.