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Build E-Commerce Apps with Reactive Programming in Spring Boot

Spring WebFlux Controller

Explore how to build a reactive web controller using Spring WebFlux within a Spring Boot application. Learn to create a ServerController that streams data asynchronously using Flux, implement a service that generates reactive data streams, and understand how Spring manages this flow. Gain hands-on experience running a simple reactive service that continuously delivers streamed content, preparing you to build efficient, event-driven web applications.

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Now that we’ve taken an initial tour through a bare Spring Boot project, we can code our first controller.

Creating a Spring WebFlux controller

Let’s start by reviewing the ServerController class that we created:

Java
package com.greglturnquist.hackingspringboot.reactive;
import reactor.core.publisher.Flux;
import org.springframework.http.MediaType;
import org.springframework.web.bind.annotation.GetMapping; 
import org.springframework.web.bind.annotation.RestController;
@RestController //1
public class ServerController {
  private final KitchenService kitchen; //2
  public ServerController(KitchenService kitchen) { 
    this.kitchen = kitchen;
  }
  @GetMapping(value = "/server", produces = MediaType.TEXT_EVENT_STREAM_VALUE) 
  Flux<Dish> serveDishes() { //3
    return this.kitchen.getDishes(); 
  }
}
ServerController class

Let’s see what the ServerController code we’ve written above is doing:

  • In line 7, @RestController is a Spring web annotation that marks this class as a controller without using any templating. Instead, it responds to web calls by serializing results and writing them straight into the HTTP response body.

  • In line 10, KitchenService (which we’ll write shortly) is provided to this controller via constructor injection. Spring seeks an instance of this service when the application starts automatically feeding it to the constructor.

  • In line 15, @GetMapping(...) is another Spring web annotation that routes HTTP GET /server calls to the serveDishes() method. . The media type it serves is text/event-stream, a stream of text that clients can easily consume, which we’ll see further down.

The Flux<Dish> object is just like what we saw earlier, a type that returns a collection of prepared meals. The most significant difference with a classic Java Collection is that each member arrives asynchronously. ...