Continuation Apex in LWC

In this blog post, we will look at how to invoke an Apex method using Continuation.

The reason behind using Continuation is when we want to make time-consuming actions (like making a callout to an external platform etc) we will be going with this option.

Let's look at the sample code (please check the comments in the code)!

public with sharing class ContinuationController {

    //Endpoint to which we will be making the callout
    private static final String LONG_RUNNING_SERVICE_URL = 'XX';
    
    //continuation and cacheale should be true!
    @AuraEnabled(continuation=true cacheable=true)
    public static Object startRequest() {
		
      //Instantiate the Continaution class
      //Also, pass the timeout when instantiation
      Continuation con = new Continuation(40);

	  //this is the callback method	
      con.continuationMethod='processResponse';
      
      //Data that you want to pass to the callback method
      con.state='Hello, World!';
	  
      //Create the request
      HttpRequest req = new HttpRequest();
      req.setMethod('GET');
      req.setEndpoint(LONG_RUNNING_SERVICE_URL);
	 
      //add the request to continuation instance
      //we can add upto 3 requests
      con.addHttpRequest(req);
      
	  //pass the continuation instance to the framework	
      return con;
    }
    
    // Callback method
    @AuraEnabled(cacheable=true)
    public static Object processResponse(List<String> labels, Object state) {
	  System.debug(' 🚀 ' +state);
      
      //labels[0] is the response of the first request
      HttpResponse response = Continuation.getResponse(labels[0]);

      String result = response.getBody();
      System.debug(' 🚀 ' +result);
      return result;
    }
}

SampleContinuationClass.cls

This is the Controller of the Web Component that invoke the apex method.

import { LightningElement, wire } from "lwc";

import startRequest from "@salesforce/apexContinuation/ContinuationController.startRequest";

export default class ContinuationComponent extends LightningElement {
  @wire(startRequest)
  records({ data, error }) {
    console.log(data);
    console.log(error);
  }
}

continuationController.js

Hope this was helpful!