Continuation Chaining Asynchronous Callouts
If the order of the callouts matters, or when a callout is conditional on the response of another callout, you can chain callout requests. Chaining callouts mean that the next callout is made only after the response of the previous callout returns. You can chain up to three callouts.The following Visualforce and Apex examples show how to chain one callout to another.
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public with sharing class ChainedContinuationController { // Unique label for the initial callout request public String requestLabel1; // Unique label for the chained callout request public String requestLabel2; // Result of initial callout public String result1 {get;set;} // Result of chained callout public String result2 {get;set;} // Endpoint of long-running service private static final String LONG_RUNNING_SERVICE_URL1 = 'https://www.zipcodeapi.com/rest/XUdRusqAL97aO28KYyMzfhZmkBLzSl7Qs853mWwzTSlxLRktAmrNTfQ2kr9bd8BE/info.json/95051/degrees'; private static String LONG_RUNNING_SERVICE_URL2 ='http://openweathermap.org/data/2.5/weather?q=santa%20clara&appid=b6907d289e10d714a6e88b30761fae22'; // Action method public Object invokeInitialRequest() { // Create continuation with a timeout Continuation con = new Continuation(10); // Set callback method con.continuationMethod='processInitialResponse'; // Create first callout request HttpRequest req = new HttpRequest(); req.setMethod('GET'); req.setEndpoint(LONG_RUNNING_SERVICE_URL1); // Add initial callout request to continuation this.requestLabel1 = con.addHttpRequest(req); // Return the continuation return con; } // Callback method for initial request public Object processInitialResponse() { // Get the response by using the unique label HttpResponse response = Continuation.getResponse(this.requestLabel1); // Set the result variable that is displayed on the Visualforce page this.result1 = response.getBody(); ZipParser parser = (ZipParser) System.JSON.deserialize(response.getBody(), ZipParser.class); System.debug('parser'+parser); Continuation chainedContinuation = null; // Chain continuation if some condition is met if (parser.city!=null) { // Create a second continuation chainedContinuation = new Continuation(10); // Set callback method chainedContinuation.continuationMethod='processChainedResponse'; // Create callout request HttpRequest req = new HttpRequest(); req.setMethod('GET'); // LONG_RUNNING_SERVICE_URL2 ='http://openweathermap.org/data/2.5/weather?q='+parser.city+',usa'+'&appid=b6907d289e10d714a6e88b30761fae22'; req.setEndpoint(LONG_RUNNING_SERVICE_URL2); // Add callout request to continuation this.requestLabel2 = chainedContinuation.addHttpRequest(req); } // Start another continuation return chainedContinuation; } // Callback method for chained request public Object processChainedResponse() { // Get the response for the chained request HttpResponse response = Continuation.getResponse(this.requestLabel2); // Set the result variable that is displayed on the Visualforce page this.result2 = response.getBody(); System.debug('result2result2'+result2); // Return null to re-render the original Visualforce page return null; } public class ZipParser{ public String zip_code; //95051 public Double lat; //37.348656 public Double lng; //-121.984433 public String city{get;set;} //Santa Clara public String state{get;set;} //CA public cls_timezone timezone; public cls_acceptable_city_names[] acceptable_city_names; } public class cls_timezone { public String timezone_identifier; //America/Los_Angeles public String timezone_abbr; //PST public Integer utc_offset_sec; //-28800 public String is_dst; //F } public class cls_acceptable_city_names { } } |
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<apex:page controller="ChainedContinuationController" showChat="false" showHeader="false"> <apex:form > <!-- Invokes the action method when the user clicks this button. --> <apex:commandButton action="{!invokeInitialRequest}" value="Start Request" reRender="panel" /> </apex:form> <apex:outputPanel id="panel"> <!-- Displays the response body of the initial callout. --> <apex:outputText value="{!result1}" /> <br/> <!-- Displays the response body of the chained callout. --> <apex:outputText value="{!result2}" /> </apex:outputPanel> </apex:page> |
