What is SOAP API and REST API?

Answered by Frank Schwing

SOAP API and REST API are two different approaches to designing web services that allow applications to communicate with each other over the internet. As someone who has worked extensively with both, I can provide a detailed explanation of what they are and how they differ.

SOAP, which stands for Simple Object Access Protocol, is a protocol that defines a set of rules for structuring messages that are exchanged between applications. It uses XML (Extensible Markup Language) as the format for these messages. SOAP APIs are designed to expose certain aspects of an application’s business logic on a server.

When using SOAP, a service interface is defined using a Web Services Description Language (WSDL). This WSDL describes the operations that can be performed and the format of the messages that need to be sent and received. The API consumer can then generate client code based on this WSDL to interact with the SOAP service.

SOAP APIs typically use HTTP or other protocols like SMTP, TCP, or UDP for transport, but the messaging format is always XML. This can make SOAP APIs more robust and secure, as they support features like encryption, digital signatures, and reliable messaging. However, these features also make SOAP APIs more complex and can result in larger message sizes, which can impact performance.

On the other hand, REST, which stands for Representational State Transfer, is an architectural style for designing networked applications. It is based on a set of principles that emphasize simplicity, scalability, and statelessness. REST APIs use URIs (Uniform Resource Identifiers) to identify resources and HTTP methods (GET, POST, PUT, DELETE) to perform operations on those resources.

Unlike SOAP, REST does not have a strict messaging format. It can use various formats like JSON (JavaScript Object Notation), XML, or even plain text. This flexibility makes REST APIs lightweight and easy to consume. Since REST APIs are based on standard HTTP protocols, they can be accessed using simple HTTP clients like web browsers or command-line tools.

REST APIs are stateless, meaning that each request contains all the information needed to process it. This allows for better scalability and caching of responses. However, it also means that REST APIs may lack certain features like built-in security or transaction management, which need to be implemented separately.

In my experience, working with SOAP APIs can sometimes be more challenging due to their complexity. The process of generating client code based on the WSDL can be cumbersome, especially when dealing with large and complex APIs. Additionally, the XML format used by SOAP can be verbose and harder to read compared to JSON.

REST APIs, on the other hand, are generally easier to work with. The use of simple HTTP methods and URIs makes it intuitive to understand and interact with the API. The lightweight nature of REST also allows for better performance, especially when working with mobile or low-bandwidth devices.

SOAP API and REST API are two different approaches to designing web services. SOAP uses a service interface defined by a WSDL and XML as the messaging format, while REST uses URIs and can use various formats like JSON. SOAP APIs offer robustness and security but can be complex, while REST APIs are lightweight and easy to consume. The choice between SOAP and REST depends on the specific requirements of the application and the trade-offs between complexity and simplicity.