I am trying to map the following
//localhost:8080/user/login/&debug=1
...
//localhost:8080/user/&debug=1
If there is any occurrence of string '&debug=1' then execute some-controller's action.
You could use a URLMapping like this
"/**&debug=1"(controller:"defaultDebug"){
action = [GET: "show"]
}
By using the double wildcard you can catch anything that ends with &debug=1