服务器输出  字节  数据到浏览器（可用于图片）
    * 步骤：
        1. 获取字节输出流
        2. 输出数据

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

@WebServlet("/ResponseDemo04")
public class ResponseDemo04 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //设置编码
        resp.setContentType("text/html;charset=utf-8");

        //获取字节输出流
        ServletOutputStream sos = resp.getOutputStream();
        sos.write("hello，你好".getBytes("utf-8"));

    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doGet(req,resp);
    }
}