Content-Length 질문입니다.

package hello.servlet.basic.response;

import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;
import java.io.PrintWriter;

@WebServlet(name = "responseHeaderServlet", urlPatterns = "/response-header")
public class ResponseHeaderServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //[status-line]
        response.setStatus(HttpServletResponse.SC_OK);

        //[response-headers]
//        response.setHeader("Content-Type", "text/plain;charset=utf-8");
        response.setHeader("Cashe-Control", "no-cache, no-store, must-revalidate");
        response.setHeader("Pragma", "no-cache");
        response.setHeader("my-header", "hello");

        //[Header 편의 메서드]
        content(response);

        //[message body]
        PrintWriter writer = response.getWriter();
        writer.println("ok");
    }

    private void content(HttpServletResponse response) {
        response.setContentType("text/plain");
        response.setCharacterEncoding("utf-8");
    }
}

ok에 println이면 3이 출력되어야하는데 4가 출력됩니다...
print로 바꿔보면 2가 출력되고, println("o") 만 적으면 3이 출력되는데 ln붙였을 때 실제 길이에서 +1 되어야 하지 않나요? 본문이 제거된거라면 아예 0이 나와야할거같은데 이유를 잘 모르겠습니다...

찜찜해서 질문 남깁니다!