Try to dispapch the request and get the matching coroutine.

def _get_coroutine(self, request, start_response):
        '''Try to dispapch the request and get the matching coroutine.'''
        adapter = self.url_map.bind_to_environ(request.environ)
        resource, kwargs = adapter.match()
        callback = self.callback_map[resource]
        inject_extra_args(callback, request, kwargs)
        return callback(request, start_response, **kwargs)