Handler methods that declare the actual return types from:

ServletInputStream ServletRequest.getInputStream()
BufferedReader ServletRequest.getReader()
PrintWriter ServetResponse.getWriter()
ServletOutputStream ServletResponse.getOutputStream()

...fail during invocation, as the method AnnotationMethodHandlerAdapter.ServletHandlerMethodInvoker.resolveStandardArgument() is checking for an exact class match against the supertype:

else if (InputStream.class.equals(parameterType)) {
return request.getInputStream();
}
else if (Reader.class.equals(parameterType)) {
return request.getReader();
}
else if (OutputStream.class.equals(parameterType)) {
this.responseArgumentUsed = true;
return response.getOutputStream();
}
else if (Writer.class.equals(parameterType)) {
this.responseArgumentUsed = true;
return response.getWriter();
}

Attaching a test case demonstrating this.