WSDL - Bottom up and Top down

In Java, people used to write an interface first and they stick to the interface before writing the implementation class. The interface will obviously tells us what are all the input arguments, return type and exception if any. In web service the client won’t directly communicate with the implementation class.  The client used to talk with the interface. So we can do any modifications in the implementation class. 

                      

If you want to change anything in the interface like adding new service methods or adding new arguments to the existing service method leads to more problems.  All the clients using your web service would be notified to use the updated one - version 2.0. This might leads to the code change. Solution for this would be sticks to the service interface and do not alter it.

                        

But in the case web service we are writing the Implementation class first!!! Yes we are writing the HelloWorld interface and HelloWorldImpl class first. Then generated the WSDL out of it. (See the blog post How to generate the WSDL from implementation class). So which one should come first? Is it WSDL or implementation class? We can do this in either way. In our case first we have written the implementation class first and generated WSDL out of it. It is known as service first or implementation first approach or bottom up approach.

There are some tools available to generate the WSDL. So we can write a WSDL first and generate classes which are necessary for writing a web service out of it. This is known as contract first or WSDL first approach or Top down approach.