Apex Callouts
A callout is a request made to a system outside of Force.com from within the platform. There are many Web APIs, free and premium, that can be quickly integrated into your Apex code using Apex callouts. This section describes how to work with the two different styles of callouts in Force.com:
1. Calling RESTful services from Apex—Force.com includes classes for issuing HTTP and HTTPS requests, encoding and decoding URLs and Base64 content, and performing cryptographic signing and hashing often needed to comply with the security requirements of external services.
2. Calling SOAP services from Apex—Apex code can be generated directly from WSDL, producing methods for invoking an external Web service and representing the input and output data in native Apex data structures rather than SOAP.
Caution
Force.com tightly controls outbound requests from its platform. Understanding the limits before jumping into development of integrations is important. These limitations apply to both Web service callouts and HTTP requests.
Request and response messages cannot exceed the maximum Apex heap size, normally 6MB. Apex code can make a maximum of ten HTTP requests in a single transaction. By default, a single request cannot run longer than 10 seconds. If a transaction contains more than one request, the total time of all requests cannot exceed 120 seconds.