Step 4: Build the HTTP request

In this step you code the HTTP request and perform the request to the server to add two numbers.

Include code inside a TRY/CATCH block to trap runtime exceptions. Assign two values to fields in the add_in record as operands for the calculation. For details about the add_in record we use in this topic, see Step 3: Define the records. 
TRY                    
    LET add_in.a = 1     
    LET add_in.b = 2      
CATCH
    ...
  
    ...


 END TRY

Recall we defined the variable req as an object of the com.HttpRequest class earlier, see Step 2: Import extension packages (com, xml, util). We instantiate this now by invoking the com.HttpRequest.Create class method to create a URI for our HTTP request; adding to the URI string:

http[s]://host:port/resource-name[?query-params]
  1. host:port is the base URL from the server.
  2. resource-name, the resource name or name of the server function, "add" in our case.
  3. A question mark ("?"), to indicate a query string.
  4. query-params is a query string that contains two key/value pairs in the format "field=value" separated by an ampersand ("&"), for example ("a=1&b=2"). They make up the query parameters or arguments required by the server's "add" function which will be extracted for processing by the Web service. We assign the values for the calculation from the "add_in" record. 
LET req = com.HttpRequest.Create("http://localhost:8090/add?a=" || add_in.a || "&b=" || add_in.b)
In our example, we anticipate the calculator Web server is on the localhost. For a production environment you need to take care of URI parsing: making sure that the URI matches what your service expects.
Set the HTTP method with the "GET" verb to request the service from the calculator Web resource. We do this by calling the com.HttpRequest object's setMethod function referenced by the req variable. 
CALL req.setMethod("GET")
Next we add the Accept and Content-Type headers to the com.HttpRequest object referenced by the req variable by calling the setHeader function. These headers specify to the Web service how we intend to receive and deliver content in the message body's media type, JSON or XML. Our preference is for JSON. 
CALL req.setHeader("Content-Type", "application/json")
CALL req.setHeader("Accept", "application/json")
Finally, we are ready to perform the HTTP request and call the com.HttpRequest object's doRequest function.
CALL req.doRequest()

In the next step we handle the response from the Web service, Step 5: Process the HTTP response.