Work with a Continuation in an Apex Class
To work with a continuation in an Apex class, use the Apex
Before you can call an external service, you must add the remote site to a list of authorized remote sites in the Salesforce user interface. From Setup, in the Quick Find box, enter
Remote Site Settings. Select Remote Site Settings, and then click New Remote Site. Add the callout URL corresponding to
LONG_RUNNING_SERVICE_URL in the Apex Class Continuation example below.
If the callout specifies a named credential as the endpoint, you don’t need to configure remote site settings. A named credential specifies the URL of a callout endpoint and its required authentication parameters in one definition. In your code, specify the named credential URL instead of the long-running service URL.
To make a long-running callout, define an Apex method that returns a
Continuationobject. (Don’t worry about the attributes of the
@AuraEnabledannotation yet. We explain that soon.)
Set an Apex callback method to be invoked after the callout completes in the
continuationMethodproperty of the
Continuationobject. In this example, the callback method is
processResponse. The callback method must be in the same Apex class.
Set the endpoint for a callout by adding an
HttpRequestobject to the
Continuationobject. A single
Continuationobject can contain a maximum of three callouts. Each callout must have a remote site or named credential defined in Setup.
Set data to pass to the callback method in the
stateproperty of the
stateproperty has an
Objecttype so you can pass in any data type that’s supported in Apex.
Code the logic in the Apex callback. When all the callouts set in the
Continuationobject have completed, the Apex callback method,
processResponse, is invoked. The callback method has two parameters that you can access.
labels—A list of labels, one for each request in the continuation. These labels are automatically created.
state—The state that you set in the
stateproperty in your
Get the response for each request in the continuation. For example:
Here’s a complete Apex class that ties together all the earlier steps.