Java http servers don't work this way. An exception bubbles up until something catches it; it only crashes the process if there is no handler. Every java http server wraps the request processing loop and catches exceptions so that it can provide a 500 Internal Server Error response.

There are likely a million ways malformed input can make a java server throw an exception; that's typically how java handles malformed input. It just gets caught and returned as an error to the client.