Check the below video first if you are planning to use Continuation

If you are new to Continuation Object in Salesforce then would suggest to read introduction post first. In last post, we discussed how to implement limitless chaining of Continuation Object using JavaScript remoting. In this post, we would try to achieve same, but instead of using JavaScript remoting, we would be using ActionFunction.

Why do we need chaining of Continuation Object

• From Apex, we can only chain 3 Continuation Object
• If we call API synchronously, chances are very high that it will run for more than 5 sec and contributing towards Concurrent Apex limit
• Getting CPU timelimit error is also high
• Making synchronous call also means risking scalability of Salesforce instance
• You don’t want user to wait till call out completed, let them work and update user interface once response is received

Below code is assuming that Salesforce Lightning design system is uploaded as a static resource.

ContinuationDemoController.class

/**
 * @Author		:		Jitendra Zaa
 * @Date		:		31 May 2017
 * @Desc		:		Demo of Continuation Server using Action Function
 *
 * */
public class ContinuationDemoController {  

    public String result {get;set;}
    private static final String CALLOUT_URL =
        'https://node-count.herokuapp.com/';
    public String apiCount {get;set;}
    public String callBackHandlerName {get;set;}
    String continuationState = '' ;
    public ContinuationDemoController(){
        result = '';
    } 

    public Object startRequest() {
      return constructCallout(callBackHandlerName,CALLOUT_URL, apiCount);
    } 

    public Object callout1Response() {
        HttpResponse response = Continuation.getResponse(continuationState);
        result = result + 'API'+ apiCount +' processing completed
 ' ;
        return null;
    }    

    private Continuation constructCallout(String callbackMethodName,String endpointURL, String apiCount){
        Continuation chainedContinuation = null;
        chainedContinuation = new Continuation(60);
        chainedContinuation.continuationMethod=callbackMethodName;
        HttpRequest req = new HttpRequest();
        req.setMethod('GET');
        req.setEndpoint(endpointURL+apiCount);
        continuationState = chainedContinuation.addHttpRequest(req);
        return chainedContinuation;
    }
}

ContinuationDemo.page
<apex:page controller="ContinuationDemoController" standardStylesheets="false" sidebar="false" showHeader="false"
 title="Continuation Server Demo">
 <!-- <apex:slds /> -->
 <apex:stylesheet value="{!URLFOR($Resource.SLDS2_3_1, 'assets/styles/salesforce-lightning-design-system.min.css')}" />
 <div class="slds slds-box">
 <div class=" slds-m-top_xx-large slds-m-bottom_xx-large slds-m-left_xx-large slds-m-right_xx-large">
 <apex:form >
 Total API calls to make : <input type="text" value="3" placeholder="Total API calls to make, Default 3" id="txtAPICallsToMake" />
 <input value="Start Request" type="button" onclick="startRequest()"/> 

 <apex:actionFunction name="submitAPI" action="{!startRequest}" reRender="panel" oncomplete="apiComplete()">
 <apex:param name="apiCount" assignTo="{!apiCount}" value="" />
 <apex:param name="callBackHandlerName" assignTo="{!callBackHandlerName}" value="" />
 </apex:actionFunction> 

 <br /> <br />

 <apex:outputPanel id="panel">
 <apex:outputText value="{!result}" escape="false" />
 </apex:outputPanel>
 </apex:form>
 </div> 

 <div id="modalWindowMsg" style="height:640px;" class="hide">
 <section role="dialog" tabindex="-1" aria-labelledby="modal-heading-01" aria-describedby="modal-content" class="slds-modal slds-fade-in-open">
 <div class="slds-modal__container">
 <header class="slds-modal__header">
 <h2 id="modal-heading-01" class="slds-text-heading_medium slds-hyphenate">API Callout status</h2>
 </header>
 <div class="slds-modal__content slds-p-around_medium" id="modal-content" >
 <p>
 <span id="modal-content-status"> Callout is in progress</span>
 </p>
 <p>
 <div class="demo-only" style="height:3rem;">
 <div role="status" class="slds-spinner slds-spinner_medium">
 <span class="slds-assistive-text">Loading</span>
 <div class="slds-spinner__dot-a"></div>
 <div class="slds-spinner__dot-b"></div>
 </div>
 </div>
 </p>
 </div>
 <footer class="slds-modal__footer">
 <button class="slds-button slds-button_neutral" onclick="cancelModal()">Cancel</button>
 </footer>
 </div>
 </section>
 <div id="modalWindowOverlay" class="slds-backdrop slds-backdrop_open"></div>
 </div> 

 </div>

 <style>
 .modal{
 visibility: visible !important;
 opacity: 1 !important;
 transition: opacity 0.4s linear;
 }
 .hide{
 display:none;
 }
 #modal-content{
 padding: 1rem;
 }
 </style>

 <script>
 var calloutNum = 1 ;
 var totalCallout = 4;

 function openModal(){
 document.getElementById("modalWindowOverlay").classList.add('modal');
 document.getElementById("modalWindowMsg").classList.remove('hide');
 }
 function cancelModal(){
 document.getElementById("modalWindowOverlay").classList.remove('modal');
 document.getElementById("modalWindowMsg").classList.add('hide');
 calloutNum = totalCallout+1;
 }
 function startRequest(){
 openModal();
 var callnumbers = document.getElementById("txtAPICallsToMake").value;
 if(callnumbers){
 totalCallout = callnumbers;
 }

 document.getElementById("modal-content-status").innerHTML = 'Callout request started for API - '+calloutNum;
 submitAPI(calloutNum,'callout1Response');
 }

 function apiComplete(){
 if(calloutNum < totalCallout){
 calloutNum++;
 document.getElementById("modal-content-status").innerHTML = 'Callout request started for API - '+calloutNum;
 submitAPI(calloutNum,'callout1Response');
 }else{
 document.getElementById("modalWindowOverlay").classList.remove('modal');
 document.getElementById("modalWindowMsg").classList.add('hide');
 }
 }
 </script>
</apex:page>

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		https://www.jitendrazaa.com/blog/salesforce/limitless-chaining-of-continuation-object-in-salesforce/
					https://www.jitendrazaa.com/blog/salesforce/limitless-chaining-of-continuation-object-in-salesforce/#comments
		
		
		Wed, 31 May 2017 03:30:40 +0000
				
		
		
		
		
		
		http://www.jitendrazaa.com/blog/?p=6101

					
										
Check the below video first if you are planning to use Continuation

Around two years back, I posted an article on Continuation Object in Salesforce. As we know because of governor limits like concurrent Apex limit or CPU time limit errors, its always recommended to perform long running Apex process asynchronously. Processes specially like calling external API.
We can come up with multiple designs if number of APIs are less. However, you would risk scalability of Salesforce if number of APIs to be called is 10+. We cannot use chaining of continuation object directly as currently its limited to 3. If we call these API’s from Javascript (like using JavaScript remoting) then still we are using synchronous Apex which would be trade off for scalability.

In Short, below are challenges in front of us

We need to call 10+ API from Visualforce
Cannot use chaining of Continuation Object as current chaining limit is 3
Cannot invoke each API from JavaScript remoting because it will be considered as Synchronous Apex


Lots of talk, now get into action. We would discuss how to create a Continuation Server in Salesforce with the help of Continuation Object and JavaScript remoting. In this approach, we would be able to call unlimited APIs asynchronously from Salesforce.

continuationDemoJSRemoting.vfp
 <apex:page controller="ContinuationDemoJSRemoting" standardStylesheets="false" sidebar="false" showHeader="false" title="Continuation Server Demo">
 <!-- <apex:slds /> Images (loading image) are not imported using this tag -->
 <apex:stylesheet value="{!URLFOR($Resource.SLDS2_3_1, 'assets/styles/salesforce-lightning-design-system.min.css')}" /> 

 <div aria-hidden="true" style="width:100%;height:100%">
 <div class="slds slds-box slds-scope">
 <div class=" slds-m-top_xx-large slds-m-bottom_small">
 Total API calls to make : <input type="text" value="3" placeholder="Total API calls to make, Default 3" id="txtAPICallsToMake" />
 <input value="Start Request" type="button" onclick="startRequest()"/>
 </div>
 <br /> <br />

 <div>
 Note : With increase in each API count, Response time would also be increased. <br />
 <b>Responses :</b> <span id="resultContainer"></span>
 </div> 

 <div id="modalWindowMsg" style="height:640px;" class="hide">
 <section role="dialog" tabindex="-1" aria-labelledby="modal-heading-01" aria-describedby="modal-content" class="slds-modal slds-fade-in-open">
 <div class="slds-modal__container">
 <header class="slds-modal__header">
 <h2 id="modal-heading-01" class="slds-text-heading_medium slds-hyphenate">API Callout status</h2>
 </header>
 <div class="slds-modal__content slds-p-around_medium" id="modal-content" >
 <p>
 <span id="modal-content-status"></span>
 </p>
 <p>
 <div class="demo-only" style="height:3rem;">
 <div role="status" class="slds-spinner slds-spinner_medium">
 <span class="slds-assistive-text">Loading</span>
 <div class="slds-spinner__dot-a"></div>
 <div class="slds-spinner__dot-b"></div>
 </div>
 </div>
 </p>
 </div>
 <footer class="slds-modal__footer">
 <button class="slds-button slds-button_neutral" onclick="cancelModal()">Cancel</button>
 </footer>
 </div>
 </section>
 <div id="modalWindowOverlay" class="slds-backdrop slds-backdrop_open"></div>
 </div>
 </div>
</div>
 <style>
 .modal{
 visibility: visible !important;
 opacity: 1 !important;
 transition: opacity 0.4s linear;
 }
 .hide{
 display:none;
 }
 #modal-content{
 padding: 1rem;
 }
 </style>
 <script type="text/javascript">
 Visualforce.remoting.timeout = 120000;
 var apiNumber = 1;
 var totalAPICallsToMake = 3;
 var resultContainer = document.getElementById("resultContainer") ;
 var modalcontentstatus = document.getElementById("modal-content-status") ;
 var startTime,endTime,elapsedSecond; 

 function startRequest(){
 var callnumbers = document.getElementById("txtAPICallsToMake").value;
 if(callnumbers){
 totalAPICallsToMake = callnumbers;
 }
 document.getElementById("modalWindowOverlay").classList.add('modal');
 document.getElementById("modalWindowMsg").classList.remove('hide');
 submitCalls(apiNumber);
 }

 function submitCalls(count){
 modalcontentstatus.innerHTML='Callback initiated for API number - '+count;
 startTime = new Date().getTime();
 Visualforce.remoting.Manager.invokeAction(
 '{!$RemoteAction.ContinuationDemoJSRemoting.callService}',
 count,
 handleResult
 );
 }

 function handleResult(result, event){
 endTime = new Date().getTime();
 elapsedSecond = (endTime - startTime) / 1000;
 modalcontentstatus.innerHTML='Callback completed';
 if (event.status) {
 resultContainer.innerHTML=resultContainer.innerHTML+'<br /> Time Taken for API '+ apiNumber +' : '+elapsedSecond+' sec , Response : '+result;
 }

 if(apiNumber < totalAPICallsToMake){
 apiNumber++;
 submitCalls(apiNumber);
 }else{
 cancelModal();
 }
 } 

 function cancelModal(){
 document.getElementById("modalWindowOverlay").classList.remove('modal');
 document.getElementById("modalWindowMsg").classList.add('hide');
 }
 </script>
</apex:page>

ContinuationDemoJSRemoting.class
/**
 * @Author		:		Jitendra Zaa
 * @Date		:		30 May 2017
 * @Desc		:		Demo of Continuation Server using Javascript remoting
 *
 * */
public class ContinuationDemoJSRemoting {

    private static final String CALLOUT_URL = 'https://node-count.herokuapp.com/';
    private static Map<Integer,String> errors = null;

    private static void initializeErrorcodes(){
        if(errors == null){
            errors = new Map<Integer,String>();
            errors.put(2000,'The timeout was reached, and the server did not get a chance to respond.');
            errors.put(2001,'There was a connection failure.');
            errors.put(2002,'Exceptions occurred.');
            errors.put(2003,'The response hasn’t arrived (which also means that the Apex asynchronous callout framework hasn’t resumed).');
            errors.put(2004,'The response size is too large (greater than 1 MB).');
        }
    }

    @RemoteAction
    public static Object callService(Integer count){
        // Return it to the system for processing
        return constructCallout('callback1Respone',count);
    }

    public static Object callback1Respone(Object state) {
        HttpResponse response = Continuation.getResponse((String)state);
        Integer statusCode = response.getStatusCode();
        if (statusCode >= 2000) {
            initializeErrorcodes();
            return 'Continuation error: ' + errors.get(statusCode);
        }
        return response.getBody();
    }

    private static Object constructCallout(String callbackMethodName,Integer count){
        Continuation chainedContinuation = null;
        chainedContinuation = new Continuation(60);
        chainedContinuation.continuationMethod=callbackMethodName;
        HttpRequest req = new HttpRequest();
        req.setMethod('GET');
        req.setEndpoint(CALLOUT_URL+count);
        chainedContinuation.state = chainedContinuation.addHttpRequest(req);
        return chainedContinuation;
    } 

}

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