Introduction
Understanding the difference between SOAP and REST is essential for Salesforce developers integrating external systems, building APIs, or consuming web services. This guide highlights the core distinctions, practical examples, and when to choose one over the other.
High-level comparison
1. Protocol vs architectural style: SOAP (Simple Object Access Protocol) is a protocol with strict standards (XML-based, WSDL). REST (Representational State Transfer) is an architectural style that uses standard HTTP methods and can use multiple formats (JSON, XML).
2. Message format: SOAP uses XML for all messages. REST typically uses JSON (lightweight) but can also use XML, HTML, or plain text.
3. Transport: SOAP commonly uses HTTP, SMTP, or other protocols but wraps payloads in an XML envelope. REST primarily relies on HTTP and uses its verbs (GET, POST, PUT, DELETE).
4. Standards & tooling: SOAP has built-in standards for security (WS-Security), transactions, and reliable messaging. REST relies on HTTPS and custom implementations for advanced features; it is simpler and better supported by modern web frameworks.
Technical differences explained
1. Contracts and discovery: SOAP exposes a WSDL (Web Services Description Language) that defines service contract. REST may provide an OpenAPI/Swagger specification but doesn’t require one.
2. Statefulness: SOAP can be stateful (supports long-running operations with WS-* specs). REST is stateless by design: each request contains all needed information.
3. Caching: REST leverages HTTP caching (ETag, Cache-Control) effectively. SOAP responses are not cache-friendly by default.
4. Error handling: SOAP has a standardized Fault element for errors. REST uses HTTP status codes (4xx, 5xx) and often returns error details in JSON.
When to use SOAP vs REST
Use SOAP when:
– You need formal contracts (WSDL) and strict typing.
– You require advanced WS-* features: message-level security, ACID transactions, reliable messaging.
– You’re integrating with legacy enterprise systems that mandate SOAP.
Use REST when:
– You want lightweight, faster integrations (JSON over HTTP).
– You prioritize scalability, caching, and mobile or web clients.
– You prefer simple CRUD operations using HTTP verbs and resource-based URIs.
Quick examples
SOAP request (simplified):
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:urn="urn:examples:weather"
>
<soapenv:Header/>
<soapenv:Body>
<urn:GetTemperature>
<urn:City>San Francisco</urn:City>
</urn:GetTemperature>
</soapenv:Body>
</soapenv:Envelope>
REST request (GET) example:
curl -X GET "https://api.example.com/weather?city=San%20Francisco" -H "Accept: application/json"
Practical tips for Salesforce developers
– Salesforce supports both: use Apex SOAP callouts (consume WSDL via WSDL2Apex) for SOAP services and HTTPRequest/HTTP for RESTful APIs.
– For SOAP, always validate WSDL compatibility and watch out for large XML payloads (heap limits). For REST, handle JSON parsing and governor limits on callouts and CPU time.
– Consider middleware (Mulesoft, Heroku, or integration layers) when translating between SOAP and REST or when you need protocol bridging and orchestration.
Summary
SOAP and REST serve different integration needs: SOAP for formal enterprise-level contracts and advanced features; REST for simplicity, performance, and web/mobile-friendly APIs. Choose based on security, transaction needs, client types, and existing ecosystem.