I have read several posts about WSDL and SOAP but still I’m confusing the actual meanings of those terms. Now, I understand that you need to construct a request message in order to consume a webservice, would it be post or get message. When talking about SOAP based webservices, you need to communicate with a webserver via constructed XML documents that are SOAP compliant. So, you need to build that manually or using proper libraries. What about WSDL, when this thing comes in?
Wikipedia states “WSDL is often used in combination with SOAP and an XML Schema to provide Web services over the Internet. A client program connecting to a Web service can read the WSDL file to determine what operations are available on the server.”. So that means that WSDL is just some file describing what services are available on webserver, and I guess, such communication must also be done using SOAP. But if I know all the webservices I use, I mean, if they are hardcoded then that means that I’m not dealing with WSDL at all. IMHO WSDL is just for very smart systems where before using webservices a program needs to read status and determine what to read. Am I right?
WSDL is a means to describe what operations (method) the webservice has as well as the input/output of those methods. In the past, way before the mobile becomes popular, WSDL is used as a means for creating what is known as a stub/proxy classes.
These classes is basically generated by specific Generator (such as WSDL2Java for Java or WSDL.exe for .NET) whose job is to read the WSDL, get the methods along with its input/output and generate a language specific classes to expose those services natively. In effect, it is hiding the SOAP messages from the user and the from the consumer of the webservice point of view, they are dealing with the native classes of their language of choice.
WebService with SOAP thus was heralded as means of integration between heterogeneous systems, allowing a communication that is language independent. For example the language for implementation for the service could be in C# but the consumer of the webservices can be in Java. If the consumer is Java programmer, by using the WSDL to auto generate the classes, the Java programmers don’t even need to know the concept of SOAP or XML. All the programmers know that they are dealing with Java object.
Nowadays, SOAP is more transparent and well known than it was in the past. As a result, by choice programmer can directly code the SOAP message, bypassing the need to generate the code via WSDL