Step 5: Process the HTTP response

In the final step you process the HTTP response; check for errors, and process the data.

At this stage a response to our request from the Web service has been received and is stored in the variable, resp. We defined the variable resp as an object of the com.HttpResponse class earlier, see Step 2: Import extension packages (com, xml, util). Now it is time to process the response.
LET resp = req.getResponse()
Start checking for errors. First get the HTTP status code returned in the response by calling the com.HttpResponse object's getStatusCode function referenced by the resp variable. Assign the status code to the "status" field of the info record ( for details about this record see Step 3: Define the records).
LET info.status = resp.getStatusCode()
The standard HTTP code of 200 indicates a successful operation, so we check for this before looking at the data.
IF info.status = 200 THEN 
If the HTTP response was good, we save the value for Content-type response header to the "resptype" field of the info record. The Content-type header defines the type associated with the message body's byte sequence. REST APIs commonly use "application/json"or "application/xml" to reveal the format of the message body.
LET info.resptype = resp.getHeader("Content-Type")

Process for XML

IF info.resptype.getIndexOf("/xml",1) THEN
    LET doc = resp.getXmlResponse()                  
    LET node = doc.getDocumentElement()
    CALL xml.Serializer.DomToVariable(node, add_out) 
    LET info.response = node.toString()
ELSE # JSON response processing
If the Content-type indicates XML format, we store the HTTP response as data in the xml.DomDocument object referenced by the doc variable using the getXmlResponse function. We then get a reference to the root node of the doc variable object by instantiating the node variable defined as an object of the xml.DomNode class using the getDocumentElement function.

Recall the doc and node variables were defined earlier, see Step 2: Import extension packages (com, xml, util).

To serialize the XML data into the add_out variable, we pass a reference to the node object variable in a call to the xml.Serializer.DomToVariable function. To convert the data referenced in the node object variable to string, we use the xml.DomNode.toString function to store it in the "response" field of the info record.

Process for JSON

If the Content-type does not indicate XML format, then we process the response for JSON, as we anticipate this as the only other option REST APIs use to format the message body.

We store the HTTP response as a string in the "response" field of the info record with a reference to the resp variable, object of the com.HttpResponse class, using the getTextResponse function. Then we pass a reference to the info record in a call to the util.JSON.parse() function to convert the HTTP response to JSON format into the add_out record.
IF info.resptype.getIndexOf("/xml",1) THEN
   # XML  response processing
ELSE # JSON response processing
     LET info.response = resp.getTextResponse()  
     CALL util.JSON.parse(info.response, add_out)

Outputting to the display

Finally, we output the HTTP response to the display depending on the status code.
IF add_out.status.code = 0 THEN
    DISPLAY add_in.a, "+", add_in.b, "=", add_out.r # Display the response, status and result
    DISPLAY "[", add_out.status.code, "] ", add_out.r

Handling Errors

If the HTTP request failed, we handle the error by formatting the HTTP response status code and description into the "response" field of the info record. Other program errors are caught in the CATCH block and stored in "result" fields of the info record.
    IF info.status = 200 THEN 
        LET info.response = SFMT("[%1] %2",resp.getStatusCode(), resp.getStatusDescription())
    END IF
    # Catch other runtime execution errors from the sqlca diagnostic record
     LET info.result.code = status
     LET info.result.desc = sqlca.sqlerrm

This completes the tutorial for the calculator demo client application. We have seen the basic steps that a RESTful client application must perform in order to carry out a simple request to a Web service. To review the complete source code, see The RESTful calculator demo source.

Each Web services client application will be different in the type of processing that is done. For more examples of Web service applications, see the code samples provided with the package in demo/WebServices.