servlet配置

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">
<!--    配置servlet标签包含名字（可以自己起名）和继承HttpServlet类路径-->
    <servlet>
        <servlet-name>haha</servlet-name>
        <servlet-class>com.example.demo.First</servlet-class>
    </servlet>
    <!--    配置servlet-mapping标签包含名字（和servlet标签名字一致）和url-pattern（form表单action值一样）-->
    <servlet-mapping>
        <servlet-name>haha</servlet-name>
        <url-pattern>/zhuce</url-pattern>
    </servlet-mapping>
</web-app>

public class First extends HttpServlet {

    @Override
    public void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
     doPost(req,resp);

    }
    
    @Override
    public void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String username = req.getParameter("username");
        String password = req.getParameter("password");
//        UserDao userDao = new UserDao();
//        int t = userDao.save(username,password);
//        System.out.println(t);
        resp.setCharacterEncoding("utf-8");
        req.setCharacterEncoding("utf-8");
        resp.setContentType("text/html");
       PrintWriter writer = resp.getWriter();

        UserDao userDao = new UserDao();
        List<User> list = userDao.selectById(password);
        for (User us : list) {
            writer.println("password:"+"  " + us.getPassword()+"  "+"username:"+"  "+us.getUsername()+"</br>");
        }
    }
}