SOAP is a protocol used for exchanging structured information in web services. It allows applications to communicate over the internet using XML-based messages and is designed for secure, reliable, and structured communication between systems.
Key Features of SOAP:
-
Uses XML for Message Formatting
- SOAP messages are structured using XML, which makes them platform-independent but also more verbose than JSON-based REST APIs.
-
Transport Protocol Independence
- While SOAP commonly uses HTTP and HTTPS, it can also work with other protocols like SMTP, FTP, and TCP.
-
Strict Standards & Security
- SOAP follows WS-Security standards, making it a better choice for secure transactions (e.g., in banking and healthcare systems).
-
Built-in Error Handling
- SOAP has a well-defined fault handling mechanism, making it easier to manage errors and exceptions.
-
Supports Statefulness
- Unlike REST (which is stateless), SOAP can maintain state, which is useful for complex transactions.
SOAP Message Structure (Example)
A SOAP request is an XML document with an Envelope, Header, and Body.
Example SOAP Request:
<![CDATA[<span class="pln">
</span><span class="pun"><?</span><span class="pln">xml version</span><span class="pun">=</span><span class="str">"1.0"</span><span class="pln"> encoding</span><span class="pun">=</span><span class="str">"UTF-8"</span><span class="pun">?></span><span class="pln">
</span><span class="tag"><soap:Envelope</span><span class="pln"> </span><span class="atn">xmlns:soap</span><span class="pun">=</span><span class="atv">"http://schemas.xmlsoap.org/soap/envelope/"</span><span class="tag">></span><span class="pln">
</span><span class="tag"><soap:Header></span><span class="pln">
</span><span class="tag"><AuthToken></span><span class="pln">123456</span><span class="tag"></AuthToken></span><span class="pln">
</span><span class="tag"></soap:Header></span><span class="pln">
</span><span class="tag"><soap:Body></span><span class="pln">
</span><span class="tag"><GetUserDetails</span><span class="pln"> </span><span class="atn">xmlns</span><span class="pun">=</span><span class="atv">"http://example.com/user"</span><span class="tag">></span><span class="pln">
</span><span class="tag"><UserID></span><span class="pln">1</span><span class="tag"></UserID></span><span class="pln">
</span><span class="tag"></GetUserDetails></span><span class="pln">
</span><span class="tag"></soap:Body></span><span class="pln">
</span><span class="tag"></soap:Envelope></span><span class="pln">
</span>]]>
Example SOAP Response:
<![CDATA[<span class="pln">
</span><span class="pun"><?</span><span class="pln">xml version</span><span class="pun">=</span><span class="str">"1.0"</span><span class="pln"> encoding</span><span class="pun">=</span><span class="str">"UTF-8"</span><span class="pun">?></span><span class="pln">
</span><span class="tag"><soap:Envelope</span><span class="pln"> </span><span class="atn">xmlns:soap</span><span class="pun">=</span><span class="atv">"http://schemas.xmlsoap.org/soap/envelope/"</span><span class="tag">></span><span class="pln">
</span><span class="tag"><soap:Body></span><span class="pln">
</span><span class="tag"><GetUserDetailsResponse</span><span class="pln"> </span><span class="atn">xmlns</span><span class="pun">=</span><span class="atv">"http://example.com/user"</span><span class="tag">></span><span class="pln">
</span><span class="tag"><User></span><span class="pln">
</span><span class="tag"><ID></span><span class="pln">1</span><span class="tag"></ID></span><span class="pln">
</span><span class="tag"><Name></span><span class="pln">John Doe</span><span class="tag"></Name></span><span class="pln">
</span><span class="tag"><Email></span><span class="pln">john@example.com</span><span class="tag"></Email></span><span class="pln">
</span><span class="tag"></User></span><span class="pln">
</span><span class="tag"></GetUserDetailsResponse></span><span class="pln">
</span><span class="tag"></soap:Body></span><span class="pln">
</span><span class="tag"></soap:Envelope></span><span class="pln">
</span>]]>
SOAP vs. REST: Key Differences
| Feature |
SOAP |
REST |
| Message Format |
XML |
JSON, XML, Plain Text |
| Protocol |
Works with HTTP, SMTP, FTP |
Only HTTP |
| Security |
More secure (WS-Security) |
Uses HTTPS, OAuth, JWT |
| Complexity |
More complex, strict standards |
Simple and flexible |
| Performance |
Slower due to XML overhead |
Faster (lightweight JSON) |
| Use Cases |
Banking, healthcare, enterprise apps |
Web & mobile applications |
There is always a discussion among integration experts with regards to which one is better: SOAP or REST. How do they compare? The following list highlights some of the comparisons between SOAP and REST:
- SOAP is a protocol, while REST is an architectural style.
- SOAP defines standards to be strictly followed, while REST doesn't define too many standards.
- SOAP requires more bandwidth and resources than REST.
- SOAP defines its own security; RESTful web services inherit security measures from the underlying transport layer.
- SOAP permits the XML data format only; REST permits different data formats, such as plain text, HTML, XML, and JSON.
In summary, REST is lighter and simpler for integration, especially with cloud web applications.
When to Use SOAP?
✅ Enterprise Applications (e.g., Banking, Healthcare)
✅ Highly Secure Transactions
✅ Stateful Operations (where maintaining session state is necessary)
✅ Reliable Messaging (ACID Transactions)
SOAP is still widely used in legacy enterprise systems but is less common in modern web and mobile applications, where RESTful APIs are preferred.
No Program Data.
