如何使用jsp+servlet实现增删改查代码功能？

package ceet.ac.cn.dao;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import ceet.ac.cn.model.Admin;
public class AdminDao {
 public List<Admin> getAllAdmin(){ //查询所有信息
 List<Admin> list = new ArrayList<Admin>(); //创建集合
 Connection conn = DbHelper.getConnection();
 String sql = "select * from admin"; //SQL查询语句
 try {
 PreparedStatement pst = conn.prepareStatement(sql);
 ResultSet rst = pst.executeQuery();
 while (rst.next()) {
 Admin admin = new Admin();
 admin.setId(rst.getInt("id")); //得到ID
 admin.setUsername(rst.getString("username"));
 admin.setUserpwd(rst.getString("userpwd"));
 list.add(admin);
 }
 rst.close(); //关闭
 pst.close(); //关闭
 } catch (SQLException e) {
 e.printStackTrace(); //抛出异常
 }
 return list; //返回一个集合
 }
 public boolean addAdmin(Admin admin){ //添加信息
 String sql = "INSERT INTO `admin`(`id`,`username`,`userpwd`) VALUES (?,?,?)"; //添加的SQL语句
 Connection conn = DbHelper.getConnection();
 try {
 PreparedStatement pst = conn.prepareStatement(sql);
 pst.setInt(1, admin.getId());
 pst.setString(2, admin.getUsername());
 pst.setString(3, admin.getUserpwd());
 int count = pst.executeUpdate();
 pst.close();
 return count>0?true:false; //是否添加的判断
 } catch (SQLException e) {
 e.printStackTrace();
 }
 return false;
 }
 public boolean updateAdmin(Admin admin){ //修改
 String sql = "UPDATE `admin` SET `username`=?,`userpwd`=? WHERE `id` = ?"; //修改的SQL语句，根据ID修改
 Connection conn = DbHelper.getConnection();
 try {
 PreparedStatement pst = conn.prepareStatement(sql);
 pst.setString(1, admin.getUsername());
 pst.setString(2, admin.getUserpwd());
 pst.setInt(3, admin.getId()); //根据的ID
 int count = pst.executeUpdate();
 pst.close(); //关闭
 return count>0?true:false; //是否修改的判断
 } catch (SQLException e) {
 e.printStackTrace();
 }
 return false;
 }
 public boolean deleteAdmin(int id){ //删除
 String sql = "delete from admin where id = ?"; //删除的SQL语句，根据ID删除
 Connection conn = DbHelper.getConnection();
 try {
 PreparedStatement pst = conn.prepareStatement(sql);
 pst.setInt(1, id);
 int count = pst.executeUpdate();
 pst.close();
 return count>0?true:false; //是否删除的判断
 } catch (SQLException e) {
 e.printStackTrace();
 }
 return false;
 }
 public Admin selectAdminById(int id){ //根据ID进行查询
 Connection conn = DbHelper.getConnection();
 String sql = "select * from admin where id = "+id;
 Admin admin = null;
 try {
 PreparedStatement pst = conn.prepareStatement(sql);
 ResultSet rst = pst.executeQuery();
 while (rst.next()) {
 admin = new Admin();
 admin.setId(rst.getInt("id"));
 admin.setUsername(rst.getString("username"));
 admin.setUserpwd(rst.getString("userpwd"));
 }
 rst.close();
 pst.close();
 } catch (SQLException e) {
 e.printStackTrace();
 }
 return admin; //返回
 }
}

package ceet.ac.cn.dao;
import java.sql.Connection;
import java.sql.DriverManager;
/**
 * 连接数据库
 * @author 画船听雨眠
 *
 */
public class DbHelper {
 private static String url = "jdbc:mysql://localhost:3306/admin"; //数据库地址
 private static String userName = "root"; //数据库用户名
 private static String passWord = "359129127"; //数据库密码
 private static Connection conn = null;
 private DbHelper(){
 }
 public static Connection getConnection(){
 if(null == conn){
 try {
 Class.forName("com.mysql.jdbc.Driver");
 conn = DriverManager.getConnection(url, userName, passWord);
 } catch (Exception e) {
 e.printStackTrace();
 }
 }
 return conn;
 }
 public static void main(String[] args) { //测试数据库是否连通
 System.err.println(getConnection());
 }
}

package ceet.ac.cn.model;
import java.io.Serializable;
public class Admin implements Serializable{ //数据封装类
 private static final long serialVersionUID = 1L;
 private int id;
 private String username;
 private String userpwd;
 public int getId() {
 return id;
 }
 public void setId(int id) {
 this.id = id;
 }
 public String getUsername() {
 return username;
 }
 public void setUsername(String username) {
 this.username = username;
 }
 public String getUserpwd() {
 return userpwd;
 }
 public void setUserpwd(String userpwd) {
 this.userpwd = userpwd;
 }
}

package ceet.ac.cn.servlet;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import ceet.ac.cn.dao.AdminDao;
import ceet.ac.cn.model.Admin;
public class AddServlet extends HttpServlet{ //添加数据
 private static final long serialVersionUID = 1L;
 protected void doGet(HttpServletRequest req, HttpServletResponse resp)
 throws ServletException, IOException {
 this.doPost(req, resp);
 }
 protected void doPost(HttpServletRequest req, HttpServletResponse resp)
 throws ServletException, IOException {
 String username = req.getParameter("username");
 String userpwd = req.getParameter("userpwd");
 Admin admin = new Admin();
 admin.setUsername(new String(username.getBytes("ISO-8859-1"),"UTF-8")); //转值，中文需要转换为utf-8
 admin.setUserpwd(new String(userpwd.getBytes("ISO-8859-1"),"UTF-8"));
 AdminDao dao = new AdminDao();
 dao.addAdmin(admin);
 req.getRequestDispatcher("ShowServlet").forward(req, resp);
 } 
}

package ceet.ac.cn.servlet;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import ceet.ac.cn.dao.AdminDao;
public class DeleteServlet extends HttpServlet{ //删除数据
 private static final long serialVersionUID = 1L;
 protected void doGet(HttpServletRequest req, HttpServletResponse resp)
 throws ServletException, IOException {
 this.doPost(req, resp);
 }
 protected void doPost(HttpServletRequest req, HttpServletResponse resp)
 throws ServletException, IOException {
 String idStr = req.getParameter("id"); //删除数据的ID，根据ID删除
 if(idStr != null && !idStr.equals("")){
 int id = Integer.valueOf(idStr);
 AdminDao dao = new AdminDao();
 dao.deleteAdmin(id);
 }
 req.getRequestDispatcher("ShowServlet").forward(req, resp);
 }
}

package ceet.ac.cn.servlet;
import java.io.IOException;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import ceet.ac.cn.dao.AdminDao;
import ceet.ac.cn.model.Admin;
public class ShowServlet extends HttpServlet{ //显示全部数据
 private static final long serialVersionUID = 1L;
 protected void doGet(HttpServletRequest req, HttpServletResponse resp)
 throws ServletException, IOException {
 this.doPost(req, resp);
 }
 protected void doPost(HttpServletRequest req, HttpServletResponse resp)
 throws ServletException, IOException {
 AdminDao dao = new AdminDao();
 List<Admin> list = dao.getAllAdmin();
 req.setAttribute("list", list);
 req.getRequestDispatcher("index.jsp").forward(req, resp);
 } 
}

package ceet.ac.cn.servlet;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import ceet.ac.cn.dao.AdminDao;
import ceet.ac.cn.model.Admin;
public class UpdateServlet extends HttpServlet{ //修改
 private static final long serialVersionUID = 1L;
 protected void doGet(HttpServletRequest req, HttpServletResponse resp)
 throws ServletException, IOException { //查询到选中ID的值所对应的数据
 String idStr = req.getParameter("id");
 if(idStr != null && !idStr.equals("")){
 int id = Integer.valueOf(idStr);
 AdminDao dao = new AdminDao();
 Admin admin = dao.selectAdminById(id);
 req.setAttribute("admin", admin);
 }
 req.getRequestDispatcher("update.jsp").forward(req, resp);

 }
 protected void doPost(HttpServletRequest req, HttpServletResponse resp)
 throws ServletException, IOException { //根据此ID对数据的值进行修改
 String username = req.getParameter("username");
 String userpwd = req.getParameter("userpwd");
 String idStr = req.getParameter("id");
 Admin admin = new Admin();
 admin.setId(Integer.valueOf(idStr));
 admin.setUsername(new String(username.getBytes("ISO-8859-1"),"UTF-8"));
 admin.setUserpwd(new String(userpwd.getBytes("ISO-8859-1"),"UTF-8"));
 AdminDao dao = new AdminDao();
 dao.updateAdmin(admin);
 req.getRequestDispatcher("ShowServlet").forward(req, resp);
 }
}

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
 <head> 
 <title>添加</title>
 <link rel="stylesheet" href="css/index.css" type="text/css" />
 </head>
 <body>
 <form action="AddServlet" method="post">
 <table border="1" class="t1">
 <tr>
 <td colspan="2"><h1>添加管理员</h1></td>
 </tr>
 <tr>
 <td>管理员帐号:</td>
 <td><input type="text" name="username"/></td>
 </tr>
 <tr>
 <td>管理员密码:</td>
 <td><input type="password" name="userpwd"/></td>
 </tr>
 <tr>
 <td colspan="2">
 <input type="submit" value="提交"/>
 <input type="reset" value="清空"/>
 </td>
 </tr>
 </table>
 </form>
 </body>
</html>

<%@ page language="java" contentType="text/html; charset=utf-8"
 pageEncoding="utf-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>显示</title>
 <style type="text/css">
 table {
 border: 1px solid pink;
 margin: 0 auto;
 }
 td{
 width: 150px;
 border: 1px solid pink;
 text-align: center;
 }
 </style>
</head>
<body>
 <table>
 <tr>
 <td>编号</td>
 <td>帐号</td>
 <td>密码</td>
 <td>操作</td>
 </tr>
 <c:forEach items="${list}" var="item">
 <tr>
 <td>${item.id }</td>
 <td>${item.username }</td>
 <td>${item.userpwd }</td>
 <td><a href="DeleteServlet?id=${item.id }">删除</a>|<a href="UpdateServlet?id=${item.id }">修改</a></td>
 </tr>
 </c:forEach>
 <tr>
 <td colspan="6" style="text-align: left;"><a href="add.jsp">添加管理员</a></td>
 </tr>
 </table>
</body>
</html>

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
 <head> 
 <title>修改</title>
 <link rel="stylesheet" href="css/index.css" type="text/css" />
 </head>
 <body>
 <form action="UpdateServlet" method="post">
 <table border="1" class="t1">
 <tr>
 <td colspan="2"><h1>修改管理员信息</h1></td>
 </tr>
 <tr>
 <td>编号:</td>
 <td><input type="text" name="id" value="${admin.id}" readonly="readonly"/></td>
 </tr>
 <tr>
 <td>管理员帐号:</td>
 <td><input type="text" name="username" value="${admin.username}"/></td>
 </tr>
 <tr>
 <td>管理员密码:</td>
 <td><input type="text" name="userpwd" value="${admin.userpwd}"/></td>
 </tr>
 <tr>
 <td colspan="2">
 <input type="submit" value="提交"/>
 <input type="button" value="返回" onclick="history.go(-1)"/>
 </td>
 </tr>
 </table>
 </form>
 </body>
</html>

@CHARSET "UTF-8";
 table.t1 {
 margin-top:10px;
 margin-left:20px;
 margin-right:20px;
 margin-bottom:5px;
 #background-color: #FFF;
 #background:#EEF4F9;
 #border: none;
 border: 1;
 #color:#003755;
 border-collapse:collapse;
 font: 14px "宋体";
 text-align: center;
 }
 table.t1 th{
 background:#7CB8E2;
 color:#fff;
 padding:6px 4px;
 text-align:center;
 }
 table.t1 td{
 background:#C7DDEE none repeat-x scroll center left;
 color:#000;
 padding:4px 2px;
 }
 table.t1 a{
 text-decoration:none;
 height:1em;
 }
 table.t1 a:link, table.t1 a:visited{
 color:#3366CC;
 }
 table.t1 a:hover{
 color:#B50000;
 text-decoration:underline;
 }