使用servlet使用alter输出中文弹窗是出现乱码

package servlets.task5_2;

import ch5.UserInfo;
import ch5.UserBase;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
import java.io.PrintWriter;

@WebServlet("/RegisterServlet")
public class RegisterServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        PrintWriter out = response.getWriter();
        HttpSession Session=request.getSession();
        ServletContext application = request.getServletContext();
        request.setCharacterEncoding("utf-8");
        response.setContentType("text/html; charset=utf-8");
        response.setCharacterEncoding("UTF-8");
        String referer = request.getHeader("referer");
        if(referer==null ||!referer.endsWith("task5_2input.jsp")){
            response.sendRedirect("task5_2input.jsp");
            return;
        }
        String userid=request.getParameter("userid");
        String password1 =request.getParameter("password1");
        String password2=request.getParameter("password2");
        String username = request.getParameter("username");
        String sex = request.getParameter("sex"); userid = userid.trim();
        if(userid.equals("")){
            out.write("");
            out.write("<script>alert('账号不允许为空!');history.back(-1);</script>");
            return;
        }
        password1 = password1.trim();
        password2 = password2.trim();
        if(password1.equals("")){
            out.write("<script>alert('密码不允许为空!');history,back(-1);</script>");
            return;
        }
        if(!password1.equals(password2)){
            out.write("<script>alert('两次输人的密码不一致!');history.back(-1);</script>");
            return;
        }
        username = username.trim();
        if(username.equals("")){
            out.write("<script>alert('用户名不允许为空!');history,back(-1);</script>");
            return;
        }
        if(sex==null){
            out.write("<script>alert('请选择性别!');history.back(-1);</script>"); return;}
        UserInfo newUser = new UserInfo(); newUser.setUserid(userid);
        newUser.setPassword(password1); newUser.setSex(sex);
        newUser.setUserName(username);
        if(application.getAttribute("userBase")==null){
            UserBase userBase = new UserBase();
            application.setAttribute("userBase",userBase);
        }
        UserBase userBase =(UserBase)(application.getAttribute("userBase"));
        String feedback = userBase.addUser(newUser);
        if(!feedback.equals("OK")){
            out.write("<script>alert('"+feedback+"');history.back(-1);</script>");
            return;
        }
        Session.setAttribute("curUser", newUser);
        response.sendRedirect("task5_2success.jsp");
    }

}

我已经使用

        request.setCharacterEncoding("utf-8");
        response.setContentType("text/html; charset=utf-8");
        response.setCharacterEncoding("UTF-8");

设置了编码格式
可是页面的弹窗还是有乱码