WebSocket with Spring boot and Angular

1. Overview

WebSocket makes it possible to open an interactive communication between a browser (front-end) and a server (back-end).

It’s a two-way communication protocol that allows not only communication from the front-end to the back-end, but also from the back-end to the front-end as well.

In this article, I will show you how to use WebSockets in both Angular and Spring boot using SockJS, StompJS and Spring WebSocket.

This is an overview of how the final project will look like :

• A Spring boot application as the back-end that use Spring WebSocket to push notifications to a topic.
• An Angular application as the front-end that use SockJS and StompJS to subscribe to the topic, consume notifications from it and displaying them in a simple html page.

2. Create back-end

2.1. Create Spring boot app

Generate a Spring boot project using Spring intializr, with Web and Websocket dependencies selected or add them manually to your pom.xml.

<!-- pom.xml -->
<dependencies>
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-web</artifactId>
	</dependency>
	
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-starter-websocket</artifactId>
	</dependency>
</dependencies>

2.2. Implement WebSocket

1. Create a configuration Java class annotated with @EnableWebSocketMessageBroker to enable WebSockets.

@Configuration
@EnableWebSocketMessageBroker
public class WebSocketConfiguration extends AbstractWebSocketMessageBrokerConfigurer {
	
	@Override
	public void registerStompEndpoints(StompEndpointRegistry stompEndpointRegistry) {
		stompEndpointRegistry.addEndpoint("/socket")
				.setAllowedOrigins("*")
				.withSockJS();
	}

	@Override
	public void configureMessageBroker(MessageBrokerRegistry registry) {
		registry.enableSimpleBroker("/topic");
		registry.setApplicationDestinationPrefixes("/app");
	}
}

2. Create a POJO class to hold the message to be shared between the back-end and the front-end.

public class Notifications {

    private int count;

    public Notifications(int count) {
        this.count = count;
    }
    public int getCount() {
        return count;
    }
    public void setCount(int count) {
        this.count = count;
    }
    public void increment() {
        this.count++;
    }
}

3. Create a web Controller and inject SimpMessagingTemplate bean in it.

Every time the Controller is called, the Notifications.count will be incremented by one and sent to the topic using SimpMessagingTemplate.convertAndSend() method.

@RestController
public class NotificationController {

    @Autowired
    private SimpMessagingTemplate template;

    // Initialize Notifications
    private Notifications notifications = new Notifications(0);

    @GetMapping("/notify")
    public String getNotification() {

        // Increment Notification by one
        notifications.increment();

        // Push notifications to front-end
        template.convertAndSend("/topic/notification", notifications);

        return "Notifications successfully sent to Angular !";
    }
}

3. Create front-end

3.1. Prepare Angular app

1. Create an Angular project using ng new command.

ng new websocket-front-end

2. Install StomJS and SockJS-client using npm install command.

npm install --save sockjs-client stompjs

3.2. Implement WebSocket

1. Create a service with name WebSocketService, using ng generate service command.

import {Injectable} from "@angular/core";

var SockJs = require("sockjs-client");
var Stomp = require("stompjs");

@Injectable()
export class WebSocketService {

    // Open connection with the back-end socket
    public connect() {
        let socket = new SockJs(`http://localhost:8080/socket`);

        let stompClient = Stomp.over(socket);

        return stompClient;
    }
}

Register the WebSocketService as a provider.

import {WebSocketService} from "./services/websocket.service";

@NgModule({
	...
	
	providers: [WebSocketService],
	
	....
})
export class AppModule { }

2. Inside the app.component.ts, open a connection with the back-end socket and subscribe to the notification topic.

import {Component} from '@angular/core';
import {WebSocketService} from "./services/websocket.service";

@Component({
    selector: 'app-root',
    templateUrl: './app.component.html',
    styleUrls: ['./app.component.css']
})
export class AppComponent {

    public notifications = 0;

    constructor(private webSocketService: WebSocketService) {
	
		// Open connection with server socket
        let stompClient = this.webSocketService.connect();
        stompClient.connect({}, frame => {
			
			// Subscribe to notification topic
            stompClient.subscribe('/topic/notification', notifications => {
			
				// Update notifications attribute with the recent messsage sent from the server
                this.notifications = JSON.parse(notifications.body).count;
            })
        });
    }
}

3. Display the notifications attribute inside the app.component.html.

<div style="text-align:center; margin-top: 150px;">

    <h1 style="font-size: 4em;">

        Notifications : <span style="color: red;">+{{ notifications }}</span>

    </h1>

</div>

Find the source code of this example in GitHub.

4. Conclusion

Combining the power of WebSockets and Angular can allow you to create a very interactive web applications.