Server Sent Events with WebFlux

EventViewer.js

import React, { Component } from "react";

export default class EventViewer extends Component {
  constructor() {
    super();

    this.state = { events: [] };
  }

  componentDidMount() {
    var source = new EventSource("http://localhost:8080/stream-events");
    source.onmessage = ({ data }) => {
      this.setState({
        events: [data, ...this.state.events]
      });
    };
  }

  renderEvents() {
    const { events } = this.state;
    return events.map(event => <div key={event}>{event}</div>);
  }

  render() {
    return <div>{this.renderEvents()}</div>;
  }
}

SSEController.java

import java.time.OffsetDateTime;
import org.springframework.http.MediaType;
import org.springframework.web.bind.annotation.CrossOrigin;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RestController;
import reactor.core.Disposable;
import reactor.core.publisher.DirectProcessor;
import reactor.core.publisher.Flux;

@CrossOrigin
@RestController
public class SSEController {
  // Singleton
  DirectProcessor<String> hotSource = DirectProcessor.create();

  @PostMapping(path = "/stream-events")
  public void addEvent() {
    hotSource.onNext(OffsetDateTime.now().toString());
  }

  @GetMapping(path = "/stream-events", produces = MediaType.TEXT_EVENT_STREAM_VALUE)
  public Flux<String> streamEvents() {
    return Flux.<String>create(emitter -> {

      Disposable disposable = hotSource.subscribe(event -> emitter.next(event));
      emitter.onCancel(disposable);
    });
  }
}