SOAP - introduction to SOAP (Simple Object Access Protocol)

1. What is SOAP?

  • SOAP is a protocol used for exchanging structured information in web services over the internet.

  • It relies on XML (Extensible Markup Language) to format the data.

  • SOAP can work over many protocols like HTTP, SMTP, TCP, or even JMS, though HTTP is most common.

2. Key Features

  • Platform and language independent (Java, .NET, Python, etc. can communicate).

  • Uses XML for request and response messages.

  • Extensible – supports security, transactions, etc. via standards (WS-Security, WS-AtomicTransaction).

  • Neutral transport – not tied to a specific network protocol.

3. SOAP Message Structure

A SOAP message is always an XML document with the following parts:

<soap:Envelope>
   <soap:Header> 
      <!-- Optional metadata, e.g., authentication info -->
   </soap:Header>
   <soap:Body>
      <!-- Main message/request/response -->
   </soap:Body>
   <soap:Fault>
      <!-- Error messages (optional) -->
   </soap:Fault>
</soap:Envelope>

  • Envelope: Root element, defines the start and end of the message.

  • Header: Optional, contains metadata (security, routing, etc.).

  • Body: Mandatory, contains actual request or response data.

  • Fault: Optional, used when errors occur.

4. Example SOAP Request

Here’s a simple SOAP request to get the weather for a city:

<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
   <soap:Body>
      <GetWeather>
         <City>New York</City>
      </GetWeather>
   </soap:Body>
</soap:Envelope>

5. SOAP vs REST (basic difference)

  • SOAP: Protocol, uses XML only, more rigid, supports advanced features (security, transactions).

  • REST: Architectural style, usually uses JSON (or XML), simpler and faster, commonly used in modern APIs.