Apex Developer Guide

Apex Developer Guide
Release Notes
Getting Started with Apex
Writing Apex
Running Apex
Invoking Apex
Apex Transactions and Governor Limits
Using Salesforce Features with Apex
Integration and Apex Utilities
Invoking Callouts Using Apex
Adding Remote Site Settings
Named Credentials as Callout Endpoints
SOAP Services: Defining a Class from a WSDL Document
Invoking HTTP Callouts
Using Certificates
Callout Limits and Limitations
Make Long-Running Callouts with Continuations
Process for Using Asynchronous Callouts
Testing Asynchronous Callouts
Asynchronous Callout Limits
Making Multiple Asynchronous Callouts
Chaining Asynchronous Callouts
Making an Asynchronous Callout from an Imported WSDL
JSON Support
XML Support
ZIP Support
Securing Your Data
Encoding Your Data
Using Patterns and Matchers
Debugging, Testing, and Deploying Apex
Apex Reference
Appendices
PDF

Note: This release is in preview. Features described here don’t become generally available until the latest general availability date that Salesforce announces for this release. Before then, and where features are noted as beta, pilot, or developer preview, we can’t guarantee general availability within any particular time frame or at all. Make your purchase decisions only on the basis of generally available products and features.

Making Multiple Asynchronous Callouts

To make multiple callouts to a long-running service simultaneously from a Visualforce page, you can add up to three requests to the Continuation instance. An example of when to make simultaneous callouts is when you’re making independent requests to a service, such as getting inventory statistics for two products.

When you’re making multiple callouts in the same continuation, the callout requests run in parallel and suspend the Visualforce request. Only after all callout responses are returned does the Visualforce process resume.

The following Visualforce and Apex examples show how to make two asynchronous callouts simultaneously by using a single continuation. The Visualforce page is shown first. The Visualforce page contains a button that invokes the action method startRequestsInParallel in the controller. When the Visualforce process resumes, the outputPanel component is rendered again. This panel displays the responses of the two asynchronous callouts.

This example shows the controller class for the Visualforce page. The startRequestsInParallel method adds two requests to the Continuation. After all callout responses are returned, the callback method (processAllResponses) is invoked and processes the responses.