SOAP

SOAP used to stand for Simple Object access protocol. Now it's simply called as SOAP. SOAP is the message format that travels between applications. It was initially developed by Developer Mentor as a platform independent way of communicating. The big success of SOAP is attributed to it's ability to travel on HTTP. (Though that ability has nothing to do with SOAP specification as such). The success of SOAP can also be attributed to it being XML based and as their is wide support for tooling for XML, it helps in dealing with SOAP.

SOAP though is more popular over HTTP however SOAP can be sent over any protocol like ftp, smtp etc. SOAP at this point exists in both 1.1 and 1.2 version. We will outline the differences between the two versions at appropriate location. In Java world, JAX-RPC supports version 1.1 and ((JAX-WS)) supports both version 1.1 and 1.2.

• SOAP message is an ordinary XML document which has following elements
• Envelope (required) – Identifies XML document as SOAP message.
• Header (optional) – Contains header information
• Body (required) – Contains call and response information
• Fault (optional) – Provides error occurred while processing the message

A typical SOAP message looks as follows:

<?xml version="1.0" encoding="UTF-8"?>

<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelop/">

  <soap:Header>

    …

  </soap:Header>

  <soap:body>

   …

  </soap:body>

</soap:Envelope>

Bring soapUI tool up and let's hit a webservice hosted by JavaSE Service endpoint. The SOAP request in this case looks like

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ws="http://ws.lalit.com/">

   <soapenv:Header/>

   <soapenv:Body>

      <ws:celsiusToFarenheitOp>

         <arg0>?</arg0>

      </ws:celsiusToFarenheitOp>

   </soapenv:Body>

</soapenv:Envelope>

In place of ?, the value is send to the server. This the whole SOAP message which travels on the wire. If we put a value of 50 and call the webservice, the response we get is:

<S:Envelope xmlns:S="http://schemas.xmlsoap.org/soap/envelope/">

   <S:Body>

      <ns2:celsiusToFarenheitOpResponse xmlns:ns2="http://ws.lalit.com/">

         <return>122.0</return>

      </ns2:celsiusToFarenheitOpResponse>

   </S:Body>

</S:Envelope>

In essence SOAP represent the message that travels as part of request and response. The popularity of SOAP comes from it being in XML format which makes it language and platform independent. Travelling over HTTP helps it to cross firewalls also. Being a XML, SOAP is amenable to XML processsing tools. SOAP messages are for application to generate and consume. A video explaining the SOAP: