Get Response When It is Ready In Spring Boot - spring-boot

Question

I have front-end(script) and back-end(Spring-Boot) code.
In backend code:
#GetMapping("/calldata")
public Response call() {
...//Imagine this operations take more than 5 minutes.
}
In font-end code:
I just call this backend api and open socket and wait until data is ready in loading state.
Is there a way to say from backend to frontend; "Don't wait to me. I will notify to you when I am ready. And I will serve my data."?

Answer 1

You want you request to be handled asynchronously. You can use websockets which keeps a single persistent connection open between server and client.
https://www.baeldung.com/spring-websockets-sendtouser

Answer 2

I had the same problem and my solution include a combination of WebSocket and Async programming. The good thing about this approach is, you can still call your REST endpoint normally. I am using SpringBoot and Angular 9. Here is what I did:
Create an async service on BE
Create WebSocket on BE
Create WebSocket on FE
Create a common topic and let FB and BE listen to it, where BE will push the response and FE and read from it.
Create a void controller method and call the async service's method
a. By doing this, your FE will not wait for the server response and your async service can continue to process the request.
Once your service is done processing, push the response to a websocket topic
Listen to the topic on your FE, and once BE pushes the response you'll be able to handle it on FE.
Here is the sample code:
Index.html:
<script>
var global = global || window;
var Buffer = Buffer || [];
var process = process || {
env: { DEBUG: undefined },
version: []
};
</script>
FE WebSocket congif file:
import * as Stomp from 'stompjs';
import * as SockJS from 'sockjs-client';
export class WebSocketAPI {
// localWebSocketEndpoint = 'http://localhost:8080/ws';
webSocketEndpoint = '/ws';
topic = '/topic/greetings'; // this is the topic which will be used to exchagne data
stompClient: any;
constructor() { }
connect() {
let ws = new SockJS(this.webSocketEndpoint);
this.stompClient = Stomp.over(ws);
const that = this;
that.stompClient.connect({}, function (frame) {
that.stompClient.subscribe(that.topic, function (sdkEvent) {
that.onMessageReceived(sdkEvent);
})
})
}
disconnect() {
if (this.stompClient !== null) {
this.stompClient.disconnect();
}
}
// you don't need this
send(name) {
this.stompClient.send('/app/hello', {}, JSON.stringify({name: name}));
}
// this is where you will receive your data once Server is done process
onMessageReceived(message) {
console.log('received: ', message);
// this.app.handleMessage(message.body);
}
}
BE Controller method:
#GetMapping("/calldata")
#ResponseStatus(value = HttpStatus.OK)
#LogExecutionTime
public void call() {
asyncService.processAsync();
}
AsyncService:
#Service
public class AsyncService {
#Autowired
private SimpMessagingTemplate simpMessagingTemplate;
#LogExecutionTime
#Async("asyncExecutor")
public void processAsync() {
// do your processing and push the response to the topic
simpMessagingTemplate.convertAndSend("/topic/greetings", response);
}
}
WebSocketConfig:
#Configuration
#EnableWebSocketMessageBroker
public class WebSocketConfig implements WebSocketMessageBrokerConfigurer {
#Override
public void configureMessageBroker(MessageBrokerRegistry registry) {
registry.enableSimpleBroker("/topic");
registry.setApplicationDestinationPrefixes("/app");
}
}
And finally AsyncConfig:
#Configuration
#EnableAsync
public class AsyncConfiguration {
#Bean(name = "asyncExecutor")
public Executor asyncExecutor() {
ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
executor.setCorePoolSize(3);
executor.setMaxPoolSize(10);
executor.setQueueCapacity(100);
executor.setThreadNamePrefix("AsynchThread-");
executor.initialize();
return executor;
}
}
Hope this will help you as well.