public function getParam($key)
    {
        if (!isset($this->params[$key])) {
            throw new InvalidArgumentException("The request parameter with key '$key' is invalid."); 
        }
        return $this->params[$key];
    }
public function getParam($key)
    {
        if (!isset($this->params[$key])) {
            throw new InvalidArgumentException("The request parameter with key '$key' is invalid."); 
        }
        return $this->params[$key];
    }
public function getParam ( $ key ) { if ( ! isset ( $ this -> params [ $ key ] ) ) { throw new InvalidArgumentException ( "The request parameter with key '$key' is invalid." ) ; } return $ this -> params [ $ key ] ; }
Get specific parameter.

@return mix
@throws \InvalidArgumentException
Get specific parameter .