Important Fact
I forgot to mention an important factor in the question. I am running this in a TestCase. I think this issue has something to do with the TestCase not awaiting for async completionHandler to return
Migrated out from Alamofire to SwiftHTTP, since I found this much easier.
On SwiftHHTP there is no way to know what URL got generated, what error it returned. For example, I tried to see the opt.debugDescription variable, it returned something cryptic like description String "<SwiftHTTP.HTTP: 0x60000007e540>"
Steps I have followed
- I have set 
YEStoAllow Arbitrary Loads. - Safari on the iPhone Simulator responds with the correct JSON if I paste 
fullurl ->http://120.0.0.1:8080/myapi/Driver/getDriver?driver=2243&domain=4345&key=asdfasdf. Evencatalina.outon the tomcat server running on my mac responds with a debug message. 
But when I run this in a test case under Xcode the below code prints none of debug print's.
- --1->, --2-->, --3-->, nothing got printed.
 - Debugger breakpoints also dont stop here.
 
CODE
var getData = [String:String]()
       getData = ["domain": "4345",
           "driver" : "2343",
           "key" : "asdfasdf"]
       var urlComponents = URLComponents(string: fullURL)!
       var queryItems = [URLQueryItem]()
       queryItems = self.getData.map{ URLQueryItem(name : $0.0, value : $0.1) }
       urlComponents.queryItems = queryItems
       print("fullurl ->"+(urlComponents.url)!.absoluteString)
       do {
           let opt = try HTTP.GET((urlComponents.url)!.absoluteString)
                      opt.start { response in
               if let err = response.error {
                   print("--1-> error: \(err.localizedDescription)")
                   return //also notify app of failure as needed
               }
               print("--2--> opt finished: \(response.description)")
               self.responseData = response
           }
       } catch let error {
           print("--3--> got an error creating the request: \(error)")
       }    
EDIT
Even after changing the code to https or http://www.google.com, same result.
let testComponents = URLComponents(string: "https://www.google.com")!
        URLSession.shared.dataTask(with: (testComponents.url)!, completionHandler: {
            (data, response, error) in
            if(error != nil){
                print("..1>..")
            }else{
                do{
                    print ("..2>.." )
                    let json = try JSONSerialization.jsonObject(with: data!, options:.allowFragments) as! [String : AnyObject]
                    self.responseData = json
                }catch let error as NSError{
                    print("..3>..")
                }
            }
        }).resume()
EDIT 1 Tried from here @Vivek's answer.
callWebService(url: (urlComponents.url)!.absoluteString)
.
.
func callWebService(url : String) {
.
.
let callURL = URL.init(string: url)
Nothing got printed again, Error / JSON, nothing.