Output to file

Hi Guys! 

I have a page, i call this page from cron, and i want to save the response (rendered page) html to a file, how can i get the output?

In CI3 Documentation i found Output class, but in CI4 how?

Now i use ob_start-ob_get_clean to get output, but in CI4 has any built in workaround? 

Thanks

Sorry for bad english