Java Spring Boot Rest Api Interview Questions

In this article, we have compiled a list of common interview questions related to Java Spring Boot REST API development. These questions cover a broad range of topics, including basic concepts of Spring Boot and RESTful web services, best practices for building and testing REST APIs, and more advanced topics such as authentication and versioning. These questions will help interviewees assess their knowledge and proficiency in Spring Boot REST API development and help them prepare for job interviews in this field.

What is Spring Boot?

Spring Boot is a framework that simplifies the development of web applications in Java. It provides a set of tools and libraries to quickly build web applications using the Spring framework. It focuses on convention over configuration and allows developers to easily configure and run Spring applications with minimal setup.

What are some topics that can be prepared for Spring Boot REST API interviews, and why are they important to know?

Here are some topics that can be prepared for Spring Boot REST API interviews:

  1. RESTful web services and architecture
  2. HTTP methods and their use cases
  3. Spring Boot and its advantages
  4. Dependency Injection and Inversion of Control (IoC)
  5. Annotations in Spring Boot
  6. Controllers and Routing
  7. Request and Response handling
  8. JSON serialization and deserialization
  9. Exception handling
  10. Validation and Data binding
  11. Spring Data JPA and Hibernate
  12. Querying data using Spring Data JPA
  13. Pagination and Sorting
  14. Caching and its implementation
  15. Security and Authentication using Spring Security
  16. OAuth 2.0 and JWT implementation
  17. Testing RESTful web services
  18. Asynchronous programming using CompletableFuture
  19. Scheduling using @Scheduled annotation
  20. Microservices and their implementation.

Preparing for these topics can help you to have a good grasp of the Spring Boot REST API concepts and be well-equipped for any interview questions that may come up.

What are the advantages of using Spring Boot?

The advantages of using Spring Boot are:

  • Faster development time
  • Reduced boilerplate code
  • Embedded servers for easier deployment
  • Auto-configuration of Spring dependencies
  • Easy integration with other Spring projects
  • Easy testing

What is REST API?

REST API (Representational State Transfer Application Programming Interface) is an architectural style for building web services. It uses HTTP methods like GET, POST, PUT, DELETE to perform CRUD (Create, Read, Update, Delete) operations on resources. It relies on stateless, client-server communication and supports various data formats like JSON, XML, etc.

How do you create a REST API using Spring Boot?

To create a REST API using Spring Boot, follow these steps:

  • Add the Spring Web dependency to your project
  • Create a controller class with the @RestController annotation
  • Define methods in the controller class with the @RequestMapping annotation to handle HTTP requests
  • Use HTTP methods like GET, POST, PUT, DELETE to perform CRUD operations
  • Return data in the desired format like JSON, XML, etc.

What are the different HTTP methods supported by REST?

The different HTTP methods supported by REST are:

  • GET – retrieves data
  • POST – creates new data
  • PUT – updates existing data
  • DELETE – deletes data
  • PATCH – updates a portion of the data
  • HEAD – retrieves only the headers of the data
  • OPTIONS – retrieves information about the supported methods and formats

What is @RestController in Spring Boot?

@RestController is an annotation in Spring Boot that combines the @Controller and @ResponseBody annotations. It is used to define a controller class that handles HTTP requests and returns the response as JSON, XML, or any other desired format.

What is @RequestMapping in Spring Boot?

@RequestMapping is an annotation in Spring Boot that is used to map HTTP requests to methods in a controller class. It specifies the URL pattern, HTTP method, and other parameters that the method can handle.

How do you handle exceptions in Spring Boot REST APIs?

To handle exceptions in Spring Boot REST APIs, follow these steps:

  • Create a class that extends ResponseEntityExceptionHandler
  • Override the methods that handle specific exceptions
  • Add the @ControllerAdvice annotation to the class
  • Use the ResponseEntity class to return a custom error message and HTTP status code

What is a ResponseEntity in Spring Boot?

ResponseEntity is a class in Spring Boot that represents the HTTP response sent by a REST API. It contains the response body, headers, and HTTP status code.

How do you implement authentication and authorization in Spring Boot REST APIs?

To implement authentication and authorization in Spring Boot REST APIs, you can use Spring Security. It provides various authentication and authorization mechanisms like Basic Authentication, OAuth, JWT, etc. You can configure Spring Security using the @EnableWebSecurity annotation and by defining security rules in the SecurityConfig class.

What is Swagger in Spring Boot?

Swagger is a tool that is used to create API documentation in a standardized format. It allows you to document your REST API using annotations like @Api, @ApiOperation, @ApiResponse, etc. Swagger UI provides a graphical user interface to interact with the API and test it.

What is the difference between @RequestParam and @PathVariable in Spring Boot?

@RequestParam is used to extract query parameters from the URL, whereas @PathVariable is used to extract path variables from the URL. Query parameters are optional and can be

omitted, whereas path variables are part of the URL and cannot be omitted.

What is CORS in Spring Boot?

CORS (Cross-Origin Resource Sharing) is a security feature implemented in web browsers that restricts web pages from making requests to a different domain than the one it originated from. In Spring Boot, you can configure CORS using the @CrossOrigin annotation to allow or restrict cross-origin requests.

What is HATEOAS in Spring Boot?

HATEOAS (Hypermedia As The Engine Of Application State) is a principle of RESTful web services that allows clients to discover and navigate through resources using hypermedia links. In Spring Boot, you can use the Spring HATEOAS library to add hypermedia links to your REST API responses.

How do you test a Spring Boot REST API?

To test a Spring Boot REST API, you can use tools like Postman or cURL to send HTTP requests and verify the response. You can also write unit tests using the Spring Test framework and the MockMvc class to simulate HTTP requests and responses. Integration tests can also be written using tools like JUnit and TestNG to test the API end-to-end.

What is the difference between a PUT and a POST request in REST?

A POST request is used to create a new resource on the server, whereas a PUT request is used to update an existing resource or create a new resource if it doesn’t already exist. The difference lies in the fact that a PUT request is idempotent, which means that it can be repeated without changing the result, whereas a POST request is not idempotent and can create multiple resources.

What is the difference between @Component, @Service, and @Repository in Spring Boot?

@Component is a generic stereotype annotation in Spring Boot used to mark a class as a Spring bean, whereas @Service is used to mark a class as a service layer bean and @Repository is used to mark a class as a data access layer bean. While all three annotations are similar in functionality, they help to convey the intent of the class and make the code more organized and maintainable.

How do you handle file uploads in a Spring Boot REST API?

To handle file uploads in a Spring Boot REST API, you can use the Spring MVC MultipartResolver interface, which allows you to parse multipart requests and handle file uploads. You can also use third-party libraries like Apache Commons FileUpload or Spring Content to handle file uploads.

How do you implement caching in a Spring Boot REST API?

To implement caching in a Spring Boot REST API, you can use the Spring Cache Abstraction, which provides an easy way to add caching to your application. You can use annotations like @Cacheable, @CacheEvict, and @CachePut to cache the results of method calls and reduce the number of expensive computations.

What is a DTO (Data Transfer Object) in Spring Boot?

A DTO is a design pattern in Spring Boot used to transfer data between layers of an application. It is a lightweight object that carries data between the service and the controller layers, allowing you to separate the concerns of data transfer and business logic. DTOs are useful when you need to transfer only a subset of the data or when you need to customize the data format for a particular API endpoint.

How do you handle pagination in a Spring Boot REST API?

To handle pagination in a Spring Boot REST API, you can use the Pageable interface provided by Spring Data JPA. You can pass the Pageable object as a parameter to the repository method and use the Page object to get the desired page size, page number, and sorting options. You can also add pagination parameters to the API endpoint URL to retrieve specific pages of data.

What is the difference between a synchronous and an asynchronous REST API call?

A synchronous REST API call blocks the client until the server returns a response, whereas an asynchronous REST API call returns immediately with a promise or a callback and continues to execute other tasks. Asynchronous REST API calls are useful when the server response time is unpredictable or when the client needs to perform other tasks while waiting for the response.

How do you implement versioning in a Spring Boot REST API?

To implement versioning in a Spring Boot REST API, you can use different URI paths, different HTTP headers, or different media types to differentiate between different versions of the API. You can also use the @RequestMapping annotation with the version number as a parameter to define different API versions.

What is the difference between a monolithic and a microservices architecture?

A monolithic architecture is a traditional architecture where all the components of an application are tightly coupled and deployed as a single unit. A microservices architecture, on the other hand, is an architecture where an application is broken down into smaller, independent services that communicate with each other through APIs. Microservices architecture provides better scalability, flexibility, and maintainability compared to a monolithic architecture. In a monolithic architecture, all the components share the same codebase and database, which can make it difficult to scale and maintain the application as it grows. With a microservices architecture, each service is developed and deployed independently, allowing teams to work on different services simultaneously without affecting the others. This approach also allows services to be scaled independently, improving overall system performance and resilience. However, a microservices architecture comes with its own set of challenges, such as increased complexity in managing multiple services and the overhead of coordinating communication between them.

What is Swagger Codegen in Spring Boot?

Swagger Codegen is a tool that generates code from a Swagger or OpenAPI specification. It can generate client-side and server-side code in multiple languages, including Java, based on the API specification. In Spring Boot, you can use the Swagger Codegen Maven plugin to generate Java classes based on a Swagger or OpenAPI specification.

What is the difference between an API and a web service?

An API (Application Programming Interface) is a set of protocols and tools for building software applications, whereas a web service is a specific type of API that uses HTTP as the communication protocol. Web services typically use XML or JSON to transfer data between the client and the server and follow the principles of RESTful web services.

How do you implement rate limiting in a Spring Boot REST API?

To implement rate limiting in a Spring Boot REST API, you can use libraries like Spring Cloud Gateway or Netflix Zuul, which provide rate limiting functionality out of the box. Alternatively, you can use a custom interceptor or filter to intercept incoming requests and enforce rate limits based on the client IP address or other parameters.

What is the purpose of the @Autowired annotation in Spring Boot?

The @Autowired annotation in Spring Boot is used to inject dependencies into a class automatically. When Spring Boot creates an instance of a class, it checks its dependency graph to see if there are any dependencies that it can inject automatically. If it finds a match, it injects the dependency using the @Autowired annotation.

What is the difference between a transactional and a non-transactional service method in Spring Boot?

A transactional service method is a method that is executed within a transaction, which means that all the database operations performed within the method are atomic and either succeed or fail as a unit. A non-transactional service method, on the other hand, does not execute within a transaction, which means that database operations can be committed or rolled back independently of each other.

What is the purpose of the @Valid annotation in Spring Boot?

The @Valid annotation in Spring Boot is used to validate input parameters or request bodies before they are processed. It is typically used in conjunction with the Bean Validation API, which provides a set of annotations and constraints that you can use to validate data. When you annotate a parameter or request body with @Valid, Spring Boot automatically applies the validation rules and throws a validation exception if any of the rules are violated.

What is the purpose of the @RequestBody annotation in Spring Boot?

The @RequestBody annotation in Spring Boot is used to map the request body of an HTTP request to a Java object. It is typically used in conjunction with the @PostMapping annotation to create a new resource on the server. When you annotate a method parameter with @RequestBody, Spring Boot automatically deserializes the request body into a Java object using a configured message converter.

What is the difference between a service and a repository in Spring Boot?

A service in Spring Boot is a layer of the application that contains business logic and interacts with one or more repositories to retrieve and manipulate data. A repository, on the other hand, is a layer of the application that is responsible for data access and persistence. Repositories typically use an Object-Relational Mapping (ORM) tool like Hibernate to interact with the database.

How do you implement security in a Spring Boot REST API?

To implement security in a Spring Boot REST API, you can use the Spring Security framework, which provides a comprehensive set of security features out of the box. You can configure Spring Security to handle authentication and authorization using various mechanisms, such as Basic Authentication, OAuth, JWT, etc.

What is the difference between an integration test and a unit test in Spring Boot?

An integration test in Spring Boot tests the interaction between different components of the application, including external dependencies like databases and web services. It verifies that the different components work together as expected and can handle real-world scenarios. A unit test, on the other hand, tests a single unit of code in isolation, typically a method or a class. It verifies that the unit of code behaves as expected under different inputs and edge cases.

What is the purpose of the @ExceptionHandler annotation in Spring Boot?

The @ExceptionHandler annotation in Spring Boot is used to handle exceptions thrown by a controller method. It allows you to specify a method to handle a specific exception and return a custom error message and HTTP status code. This approach helps to centralize exception handling and make the code more maintainable.

How do you implement pagination and sorting in a Spring Boot REST API?

To implement pagination and sorting in a Spring Boot REST API, you can use the Pageable interface provided by Spring Data JPA. You can pass the Pageable object as a parameter to the repository method and use the Page object to get the desired page size, page number, and sorting options. You can also add pagination and sorting parameters to the API endpoint URL to retrieve specific pages of data in the desired order.

What is the purpose of the @Transactional annotation in Spring Boot?

The @Transactional annotation in Spring Boot is used to specify that a method should execute within a transaction. It ensures that all the database operations performed within the method are atomic and either succeed or fail as a unit. The @Transactional annotation can be used at the class or method level and allows you to specify transaction propagation, isolation level, and rollback rules.

What is the purpose of the @GetMapping annotation in Spring Boot?

The @GetMapping annotation in Spring Boot is used to map an HTTP GET request to a method in a controller class. It allows you to define the URL path, request parameters, and response type for the method. When a GET request is made to the specified URL path, Spring Boot executes the corresponding method and returns the response data in the specified format.

What is the purpose of the @PathVariable annotation in Spring Boot?

The @PathVariable annotation in Spring Boot is used to map a variable part of the request URL to a method parameter. It is typically used to retrieve a specific resource by its ID or to filter resources by a specific attribute. When you annotate a method parameter with @PathVariable, Spring Boot automatically maps the corresponding part of the URL to the parameter.

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

The @RequestMapping annotation in Spring Boot is used to map an HTTP request to a method in a controller class. It allows you to define the URL path, request method, and other request parameters for the method. When a request is made to the specified URL path and method, Spring Boot executes the corresponding method and returns the response data in the specified format.

What is the purpose of the @Scheduled annotation in Spring Boot?

The @Scheduled annotation in Spring Boot is used to schedule a method to be executed at a specific time or interval. It allows you to specify the interval, delay, and time zone for the method. When you annotate a method with @Scheduled, Spring Boot automatically schedules the method to be executed according to the specified parameters.

What is the difference between a GET and a POST request in REST?

A GET request is used to retrieve data from the server, whereas a POST request is used to send data to the server to create or update a resource. The main difference between the two is that a GET request is idempotent and does not modify the state of the server, whereas a POST request is not idempotent and can modify the state of the server.

How do you implement authentication in a Spring Boot REST API?

To implement authentication in a Spring Boot REST API, you can use various mechanisms, such as Basic Authentication, OAuth, JWT, etc. You can configure Spring Security to handle authentication using these mechanisms and restrict access to certain endpoints based on user roles or permissions.

What is the purpose of the @ModelAttribute annotation in Spring Boot?

The @ModelAttribute annotation in Spring Boot is used to bind request parameters to a model attribute. It is typically used to populate a form or to update an existing resource. When you annotate a method parameter with @ModelAttribute, Spring Boot automatically maps the corresponding request parameter to the parameter and adds it to the model.

What is the purpose of the @RestController annotation in Spring Boot?

The @RestController annotation in Spring Boot is used to create a RESTful controller class that returns data in the desired format, such as JSON or XML. It combines the functionality of the @Controller and @ResponseBody annotations and eliminates the need for specifying @ResponseBody on every method.

  1. What is the difference between an ETag and a Last-Modified header in HTTP?

An ETag is a string that represents a version of a resource and is used to identify whether the resource has changed since the client last requested it. A Last-Modified header is a timestamp that indicates when a resource was last modified and is used to determine whether the resource has changed since the client last requested it. The main difference between the two is that an ETag is more accurate in detecting changes to a resource, whereas a Last-Modified header is less accurate but more efficient.

What is the purpose of the @CrossOrigin annotation in Spring Boot?

The @CrossOrigin annotation in Spring Boot is used to enable cross-origin resource sharing (CORS) for a controller method. It allows you to specify the allowed origins, methods, and headers for a method, enabling clients from different domains to access the method’s resources.

What is the difference between a stateless and a stateful REST API?

A stateless REST API is an API that does not maintain any state information between requests. Each request is treated as an independent event, and the client is responsible for managing its state. A stateful REST API, on the other hand, maintains state information between requests and uses cookies or tokens to keep track of the client’s state. Stateful REST APIs are more complex to implement and can be less scalable, but they provide more functionality and security.

How do you handle versioning in a Spring Boot REST API?

To handle versioning in a Spring Boot REST API, you can use different URI paths, different HTTP headers, or different media types to differentiate between different versions of the API. You can also use the @RequestMapping annotation with the version number as a parameter to define different API versions.

What is the purpose of the @ResponseStatus annotation in Spring Boot?

The @ResponseStatus annotation in Spring Boot is used to specify the HTTP status code to be returned by a controller method. It allows you to customize the response status code based on the outcome of the method and provide a more meaningful error message to the client.

What is the purpose of the @ExceptionHandler annotation in Spring Boot?

The @ExceptionHandler annotation in Spring Boot is used to handle exceptions thrown by a controller method. It allows you to specify a method to handle a specific exception and return a custom error message and HTTP status code. This approach helps to centralize exception handling and make the code more maintainable.

How do you handle versioning in a Spring Boot REST API?

To handle versioning in a Spring Boot REST API, you can use different URI paths, different HTTP headers, or different media types to differentiate between different versions of the API. You can also use the @RequestMapping annotation with the version number as a parameter to define different API versions.

What is the purpose of the @ExceptionHandler annotation in Spring Boot?

The @ExceptionHandler annotation in Spring Boot is used to handle exceptions thrown by a controller method. It allows you to specify a method to handle a specific exception and return a custom error message and HTTP status code. This approach helps to centralize exception handling and make the code more maintainable.

What is the purpose of the @Async annotation in Spring Boot?

The @Async annotation in Spring Boot is used to indicate that a method should be executed asynchronously in a separate thread. It allows you to perform long-running or blocking operations without blocking the main thread of the application, improving overall performance and responsiveness.

How do you implement caching in a Spring Boot REST API?

To implement caching in a Spring Boot REST API, you can use the Spring Cache abstraction, which provides a unified API for various caching providers, such as Redis, Ehcache, and Hazelcast. You can annotate a method with the @Cacheable annotation to cache the results of the method for a specific period. You can also use the @CachePut and @CacheEvict annotations to update or delete cached data.

What is the difference between a synchronous and an asynchronous REST API?

A synchronous REST API is an API where the client blocks and waits for a response from the server before proceeding with the next request. An asynchronous REST API, on the other hand, allows the client to continue with other requests while waiting for a response from the server. Asynchronous REST APIs are typically faster and more scalable but require more complex programming and error handling.

How do you handle errors in a Spring Boot REST API?

To handle errors in a Spring Boot REST API, you can use various mechanisms, such as exceptions, HTTP status codes, and error messages. You can use the @ExceptionHandler annotation to handle exceptions thrown by a controller method and return a custom error message and HTTP status code. You can also use the @ResponseStatus annotation to specify the default HTTP status code for a method.

What is the purpose of the @Scheduled annotation in Spring Boot?

The @Scheduled annotation in Spring Boot is used to schedule a method to be executed at a specific time or interval. It allows you to specify the interval, delay, and time zone for the method. When you annotate a method with @Scheduled, Spring Boot automatically schedules the method to be executed according to the specified parameters.

How do you implement pagination and sorting in a Spring Boot REST API?

To implement pagination and sorting in a Spring Boot REST API, you can use the Pageable interface provided by Spring Data JPA. You can pass the Pageable object as a parameter to the repository method and use the Page object to get the desired page size, page number, and sorting options. You can also add pagination and sorting parameters to the API endpoint URL to retrieve specific pages of data in the desired order.

What is the purpose of the @PostMapping annotation in Spring Boot?

The @PostMapping annotation in Spring Boot is used to map an HTTP POST request to a method in a controller class. It allows you to define the URL path, request parameters, and response type for the method. When a POST request is made to the specified URL path, Spring Boot executes the corresponding method and returns the response data in the specified format.

Conclusion

In conclusion, Java Spring Boot REST API interview questions cover a wide range of topics, including basic concepts, best practices, and advanced techniques. Understanding these questions and their answers is essential for anyone who wants to develop robust and scalable REST APIs using the Spring Boot framework. The questions discussed in this list cover important topics such as handling exceptions, implementing security, versioning, caching, and pagination, among others. By mastering these concepts and techniques, developers can build high-quality REST APIs that meet the needs of modern web applications.

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