java中，写一个servlet，怎么写一个弹出的消息框？

servlet中 输出 JAVASCRIPT 就是了

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

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class Test extends javax.servlet.http.HttpServlet implements javax.servlet.Servlet {

public Test() {
super();
}

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
PrintWriter pw=response.getWriter();
pw.write("");
}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doGet(request, response);
}
}