How can I read the query string parameters in my Mock class?

Question

My requirement is to call an external REST based service from a trigger. This service has been implemented with the GET method. I have finished the code for the trigger and the class.

Now I am creating test classes and a mock in place of the callout. The mock needs to send two separate responses. A success response or a failure response. Here is the mock I am currently writing.

global class RestCalloutMockImpl implements HttpCalloutMock
{
    global HTTPResponse respond(HTTPRequest req) 
    {
        HttpResponse res = new HttpResponse();
        System.Debug('Endpoint contains '+ req.getEndpoint()); //No query string parameters here.
        System.Debug('Method contains '+ req.getMethod()); //GET
        System.Debug('Body contains ' + req.getBody)); //NULL
        res.setHeader('Content-Type','application/json');
        //PSEUDOCODE follows. This is where I want to read the query string paramter values.
        if(check for parameter value here)
        {
            res.setBody('{"ErrorMessage":null,"ResultValue":"Success"}');
            res.setStatusCode(200);
        }
        else
        {   //Simulate Failure here.
            res.setBody('{"ErrorMessage":"Life is Short!","ResultValue":"Failure"}');
            res.setStatusCode(200);            
        }       
        return res;

    }
}

I have been through the documentation on the HttpRequest class. I could not find any method that will output the parameters sent on the query string.

If the calling method is a POST, the getBody() method can be used to see read the contents.

I have tried to use the RestContext class, but the value for that is NULL.

Answer 1

You can use the PageReference class to read the query string, if any, from the URL:

PageReference ref = new PageReference(req.getEndpoint());
System.debug(ref.getParameters());

If the class performing the callout does not specify a query string, then ref.getParameters() will contain no values.