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What is a SOAP API

What is SOAP API?

SOAP (Simple Object Access Protocol) is a standard messaging protocol system that was designed for Microsoft in 1998. It permits processes using different operating systems like Linux and Windows to communicate via HTTP and its XML. SOAP APIs are designed to create, recover, update and delete records like accounts, passwords, leads, and custom objects. Currently, it is mostly used to expose web services and transmit data over HTTP/HTTPS. 

SOAP based APIs take advantage of web based protocols such as HTTP  and XML, allowing developers to manipulate web services with great ease and get responses without worrying about language and platforms at all.

Unlike the REST pattern, SOAP only supports the XML data format and strongly follows preset standards such as messaging structure, a set of encoding rules, and a convention for providing procedure requests and responses.

Even though the vast majority of web data exchange happens over REST exchange, SOAP is going to be around for quite a long time. This is because SOAP is highly standardized, allows for automation in certain cases, and is more secure.

Soap API
Source: Jelvix

How does SOAP API work?

The SOAP specification describes a standard, XML-based way to encode requests and responses, including:

  • Requests to invoke a method on a service, including in parameters
  • Responses from a service method, including return value and out parameters
  • Errors from a service

SOAP describes the structure and data types of message payloads by using the emerging W3C XML Schema standard issued by the World Wide Web Consortium (W3C). SOAP is a transport-agnostic messaging system; SOAP requests and responses travel using HTTP, HTTPS, or some other transport mechanism.

In general, a SOAP service remote procedure call (RPC) request/response sequence includes the following steps:

  1. A SOAP client formulates a request for a service. This involves creating a conforming XML document, either explicitly or using Oracle SOAP client API.
  2. A SOAP client sends the XML document to a SOAP server. This SOAP request is posted using HTTP or HTTPS to a SOAP Request Handler running as a servlet on a Web server.
  3. The Web server receives the SOAP message, an XML document, using the SOAP Request Handler Servlet. The server then dispatches the message as a service invocation to an appropriate server-side application providing the requested service.
  4. A response from the service is returned to the SOAP Request Handler Servlet and then to the caller using the standard SOAP XML payload format. 

What is the SOAP structure?

The SOAP structure includes these elements:

  • The Envelope, which is the core element of every message. It begins and concludes messages with its tags, thus enveloping it.
  • The Header, which is optional, and determines the specifics, extra requirements for the message, e.g. authentication.
  • The Body includes the request or response.
  • The Fault, which is optional, displays all the data about errors that could emerge throughout the API request and response.

What is SOAP API used for?

SOAP based APIs are used for the purpose of creating, recovering, updating, and deleting records such as accounts, passwords, leads, and custom objects.

They can make more than twenty different kinds of calls that enable API developers to maintain their accounts, perform accurate searches and much more. You can then use them with all the languages that support web services.

How is SOAP API different from REST API?

The term web API generally refers to both sides of computer systems communicating over a network: the API services offered by a server, as well as the API offered by the client such as a web browser.

The server-side portion of the web API is a programmatic interface to a defined request-response message system, and is typically referred to as the Web Service. There are several design models for web services, but the two most dominant are SOAP and REST.

REST API does not have any official standard at all due to the fact that it is an architectural style. SOAP APIs, on the other hand have an official standard because SOAP is a protocol. REST is also rather different because it makes use of multiple standards like HTTP, JSON, URL, and XML while SOAP APIs is largely based on HTTP and XML. Another difference is that since REST deploys multiple standards it takes up less resources and bandwidth in comparison with SOAP that uses XML for the creation of Payload and results in the large sized file. 

Both these types of APIs even expose the business logics in different ways. REST API makes use of URL exposure like @path("/WeatherService") while SOAP API use of services interfaces like @WebService.

The SOAP API even defines too many standards and its implementer implements the things in a standard way only. Incase there is a miscommunication from service, the result will be an error. REST APIs don’t focus much on too many standards, which may result in a corrupt API in the end.

REST API makes use of the Web Application Description Language, and SOAP API employs the Web Services Description language to describe the functionalities being offered by web services. 

Both REST and SOAP APIs are convenient when used with JavaScript, but while SOAP APIs do not support greater implementation, REST APIs can be implemented with great ease.

SOAP provides the following advantages when compared to REST:

  • Language, platform, and transport independent (REST requires use of HTTP)     
  • Works well in distributed enterprise environments (REST assumes direct point-to-point communication)
  • Standardised
  • Provides significant pre-build extensibility in the form of the WS* standards
  • Built-in error handling
  • Automation when used with certain language products

REST is easier to use for the most part and is more flexible. It has the following advantages when compared to SOAP:

  • Uses easy to understand standards like swagger and OpenAPI Specification 3.0
  • Smaller learning curve
  • Efficient (SOAP uses XML for all messages, REST mostly uses smaller message formats like JSON)
  • Fast (no extensive processing required)
  • Closer to other Web technologies in design philosophy
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