Step 1: Obtain information about Web service resources

To access a remote RESTful Web services server, you must first get information about the services offered by a server from the service provider.

Note: This is in contrast to how you get this information when using the Simple Object Access Protocol (SOAP), where a Web Services Description Language (WSDL) file provides you with the necessary information and you can download the WSDL directly from the Web Service.

In REST, the name of the resources or functions and what query parameters or arguments to use with them are generally all that you require, as this information contains everything the client needs to interact with the required resource.

Add Function

In the code example for the Calculator RESTFul Web services server application, we know that the calculator demo service performs various calculator functions. Our client application simply wants to access the function to add values.

# Calculator Web Service add function
 
FUNCTION add()
  LET add_out.r = add_in.a + add_in.b
  LET add_out.status.code = 0
  LET add_out.status.desc = "OK"
END FUNCTION

The HTTP request must therefore use an URI with a resource name and the required parameters that matches the calculator function defined in the calculator Web service server side. Therefore, Add becomes the resource name part of the URI we need to include in our code.

# Sample request to add two numbers 

GET http://localhost:8090/add?a=1&b=2

In the next step we start to code the client application, Step 2: Import extension packages (com, xml, util)