# Custom Request and APIRoute class

In some cases, you may want to override the logic used by the `Request` and `APIRoute` classes.

In particular, this may be a good alternative to logic in a middleware.

For example, if you want to read or manipulate the request body before it is processed by your application.

/// danger

This is an "advanced" feature.

If you are just starting with **FastAPI** you might want to skip this section.

///

    * If you have advanced custom logic to access each route's `route.response_class`, or the `router.default_response_class`, or the `app.default_response_class`: the default value for `response_class` in `APIRoute` and for `default_response_class` in `APIRouter` and `FastAPI` is now a `DefaultPlaceholder` used internally to handle and solve default values and overrides. The actual response class inside the `DefaultPlaceholder` is available at `route.response_class.value`....