In this blog post, we will see how to create a REST API using Spring WebFlux. The API can be used to expose data from a database in a single RESTful service. We will use Spring Boot to setup a Spring Boot application and create a RESTful service using Spring WebFlux. We will also see how to create a transaction management to a create, update, and delete (CRUD) operations.
In this article, we’ll discuss how to develop a REST API in a Spring Boot application. We’ll be focusing in on Spring WebFlux, a reactive programming framework for building asynchronous applications.
Web development is a major trend in the software industry, and it is becoming increasingly important to have a solid programming language and framework. For every web application developer, a good language will make developing and testing the application much easier. Spring WebFlux is a popular choice for developers as it is easy to implement and test in the Java Virtual Machine (JVM). In this tutorial, we will develop a simple REST API that uses Spring WebFlux and execute it with a simple client.
This tutorial is the fifth in a series of lessons on reactive programming in Java and the Spring Framework. In this tutorial, we will develop a simple REST API with Spring Web flow. To fully understand this tutorial, you must have studied the previous tutorial and know how to develop a REST controller in blocking mode (unresponsive) with Spring Framework.Contents
Web Reactive Battery
The following figure, taken from the Spring Webflux documentation, shows how the Spring Web Reactive stack differs from and resembles the Spring MVC stack. 
Practice code
The REST API we are going to create is a simple CRUD API that will be responsible for interacting with the books stored in MongoDB. We will use Maven as a dependency management tool. The structure of the project is shown below: 
Here is the pom.xml file I used for the project: 4.0.0 org.springframework.boot spring-boot-starter-parent 2.5.0 com.sergey reactive_api 0.0.1 reactive_api demo project for spring boot 1.8 org.projectlombok lombok 1.18.20 org.springframework.boot spring-boot-starter-data-mongodb-reactive org.springframework.boot spring-boot-starter-webflux fr.flapdoodle.embed fr.flapdoodle.embed.mongo org.springframework.boot spring-boot-maven-plugin To limit the number of configurations, we will use MongoDB in memory. It is provided by the flapdoodle project library.
Model
The book entity will be the only entity in the model. Let’s assume for the sake of convenience that every book has an author. @Document @Data @NoArgsConstructor public class Book { @Id private String id; private String name; private String author ; public Book(String name, String author) { this.name = name; this.author = author; } } The Lombok project was used to reduce the number of code models.
Service
I’m a big fan of SOLID principles, so let’s make them abstractions. There will be an interface for the service and the implementation of the service.
Interface
public interface BookService { Mono getBookById(String id) ; The getAllBooks() thread; Mono DeleteBookToId(String id) ; Mono deleteAllBooks() ; Mono createBook(Book) ; Mono updateBook(Book book); }
Version
@Service public class BookServiceImple implements BookService { private final BookRepository bookRepository ; public BookServiceImpl(BookRepository bookRepository) { this.bookRepository = bookRepository ; } private Book formatBook(Book Book) { book.setName(book.getName().toLowerCase()); book.setAuthor(book.getAuthor().toUpperCase()); return book; } @Override public Mono getBookById(String id) { return bookRepository.findById(id) .map(this::formatBook); } @Override public Flux getAllBooks() { return bookRepository.findAll().map(this::formatBook); } @Override public Mono deleteBookById(String id) { return bookRepository.deleteById(id); } @Override public Mono deleteAllBooks() { return bookRepository.deleteAll(); } @Override public Mono createBook(Book book book) { if (book.getId() != null) { return Mono.error(new IllegalArgumentException(Id of new book must be null)); } return bookRepository.save(book); } @Overridepublic Mono updateBook(Book book) {return bookRepository.existsById(book.getId()).flatMap(isExisting ->{if (isExisting) {return bookRepository.save(book);} else {return Mono.error(new IllegalArgumentException(The book id must exist for the update to take place));}});} The implementation class can be extended with additional logic if necessary.
Recovery controller
When using Spring Webflux, there are two ways to create a controller:
1) Use annotations as in Spring MVC.
This is the easiest method for those familiar with Spring MVC. Here is the controller class with all the CRUD methods: @RestController @RequestMapping(/v1/annotated/books) public class AnnotationController { private final BookService bookService ; public AnnotationController(BookService bookService) { this.bookService = bookService; } @GetMapping public Flux getAllBooks() { return bookService.getAllBooks(); } @GetMapping(/{id}) public Mono getBookById(@PathVariable String id) { return bookService.getBookById(id); } @PostMapping @ResponseStatus(HttpStatus.CREATED) public Mono createBook(@RequestBody Book book) { return bookService.createBook(book); } @PutMapping public Mono updateBook(@RequestBody Book book book) { return bookService.updateBook(book); } @DeleteMapping(/{id}) public Mono deleteBookById(@PathVariable String id) { return bookService.deleteBookById(id); } @DeleteMapping public Mono deleteAllBooks() { return bookService.deleteAllBooks(); } }
2) Use of functional criteria
These endpoints are created in a functional programming style. This means he uses lambda expressions a lot. This method is simpler than the annotation method because it uses the same Reactive Core Foundation. It uses a functional programming model in which functions are used to route and process requests. @Configuration @EnableWebFlux public class FunctionalController { private static String BASE_URL = /v1/functional/books; private final BookService bookService ; public FunctionalController(BookService bookService) { this.bookService = bookService; } @Bean public RouterFunction getAllBooks() { return RouterFunctions.route() .GET(BASE_URL, request -> ServerResponse.ok().body(bookService.getAllBooks(), Book.class).build(); } @Bean public RouterFunction getBookById() { return RouterFunctions.route() .GET(BASE_URL.concat(/{id}), request -> { String id = request.pathVariable(id); return ServerResponse.ok().body(bookService.getBookById(id), Book.class); }).build(); } @Bean public RouterFunction createBook() { return RouterFunctions.route() .POST(BASE_URL, request -> request.bodyToMono(Book.class) .flatMap(bookService::createBook) .flatMap(book -> ServerResponse.status(HttpStatus.CREATED) .body(book, Book.class)) .build(); } @Bean public RouterFunction updateBook() { return RouterFunctions.route() .PUT(BASE_URL, request -> request.bodyToMono(Book.class) .flatMap(bookService::updateBook) .flatMap(book -> ServerResponse.ok() .body(book, Book.class)) .build(); } @Bean public RouterFunction deleteBookById() { return RouterFunctions.route() .DELETE(BASE_URL.concat(/{id}), request -> { String id = request.pathVariable(id); return ServerResponse.ok().body(bookService.deleteBookById(id), Void.class); }).build(); } @Bean public RouterFunction deleteAllBooks() { return RouterFunctions.route() .DELETE(BASE_URL, request -> ServerResponse.ok() .body(bookService.deleteAllBooks(), Void.class)).build(); } } The class RouterFunction represents the main entry point of the query when we use a functional style. It accepts the request and returns a response, wrapped in a class ServerResponse. It can be considered the equivalent of query mappings and associated methods when using the annotated style. The RouterFunctions class is a class used to build RouterFunctions according to the Builder model. We use it to specify the structure of the request and how the request is used to form the response. You can read in detail how this works in the RouterFunctions section of the Webflux documentation. You can test the application by adding a bootstrap class that loads some data into the database, then use POSTMAN or a similar tool to test different endpoints. @Component @Slf4j public class Bootstrap implements CommandLineRunner { private final BookRepository bookRepository ; public Bootstrap(BookRepository bookRepository) { this.bookRepository = bookRepository; } @Override public void run(String… args) throws Exception { Book book1 = new Book(Docker In Action, Florian Lowe); Book book2 = new Book(Java Best Practices, Sergey); Book book3 = new Book(Reactive Programming in C#, Satoshi Nakamoto) ; bookRepository.saveAll(Arrays.asList(book1, book2, book3)) .subscribe(book -> log.info(save books with name: {}, book.getName()); } } This is the end of this manual. You can now use Spring Webflux to work on different projects. I hope this was helpful. Until the next lesson.In this blog post, I will talk about how we have developed a REST API using Spring Webflux. The REST API allows users to search for video equipment. Each search can also include the filters of price, brand and model to narrow down the results.. Read more about spring webflux crud example and let us know what you think.
Frequently Asked Questions
What type of API is spring WebFlux?
The REST API is a way of allowing a web application to interact with another web application or external service in an efficient manner. The general method is to use HTTP or HTTPS to call the service and use JSON or XML to return the data. The advantage of the REST API is that it is simple and can be easily used in a wide range of applications. WebFlux is a fully reactive framework that makes it easy to build reactive web applications. Its core feature is the ability to define custom asynchronous tier-like services, which can be easily integrated into your web application code without any significant refactoring.
How do I create a spring REST API?
Ok in this blog post i am going to be talking about REST API’s. REST stands for ReSTful. It’s a style of service where all the requests and responses are done through URLs instead of an HTTP method, such as GET, POST, PUT, and DELETE. It’s like the opposite way of GET in a browser. I think that REST APIs are a great way to create web services. It makes it easy to share data with your clients. How do you create a Spring REST API? Is it easy? No. But, can it be done? Of course it can. In this article, I’ll guide you through creating a REST API that returns some data from the Twitter API.
How do I use WebFlux in spring boot?
WebFlux is an outstanding alternative to traditional web framework like Spring MVC, that’s easy to use but allows you to write highly scalable and flexible REST APIs. This talk will focus on how to use WebFlux in Spring Boot, as well as some of its best practices. I started using WebFlux in spring boot because I wanted to have a REST API for a video equipment company that I founded. I tried a few other WebFlux-based options, but none that I could make feel natural. I had to build some custom classes to make it easier for me to work with my existing data, and I wanted to have some kind of authentication, so I ended up using spring security for that.
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