How to give data to tomcat?

Question

Java

learning the basics of java ee (servlets, jdbc). I use tomcat for practice.

I created a simple client - I transfer text data from it, I catch it on tomcat without any problems. I'm trying to send a reply and... don't know how! In the docs for HttpServletResponse, I simply do not find any method that looks like what I need. I suffer for five hours. Help me get out of the stupor on how to send a response, or if I chose the wrong approach - show an example (or best practice) of how rest services in java usually do.