题外话：该分页显示是用 “表示层-控制层-DAO层-数据库”的设计思想实现的，有什么需要改进的地方大家提出来，共同学习进步。
思路：首先得在 DAO 对象中提供分页查询的方法，在控制层调用该方法查到指定页的数据，在表示层通过 EL 表达式和 JSTL 将该页数据显示出来。
重点：两个方法：（1）计算总的页数。 （2）查询指定页数据。
1.DAO层-数据库
JDBCUtils 类用于打开和关闭数据库，核心代码如下：
1 import java.sql.Connection;
2 import java.sql.DriverManager;
3 import java.sql.PreparedStatement;
4 import java.sql.ResultSet;
5 import java.sql.SQLException;
6
7 public class JDBCUtils {
8 private Connection conn=null;
9 private PreparedStatement pstmt=null;
10
11
12 /**
13 * connect 连接数据库
14 * @return
15 */
16 public Connection connect(){
17 String user="root";
18 String password="1234";
19 String driverClass = "com.mysql.jdbc.Driver";
20 String jdbcUrl = "jdbc:mysql://localhost:3306/book";
21
22 try {
23 Class.forName(driverClass);
24 conn = DriverManager.getConnection(jdbcUrl, user, password);
25 } catch (Exception e) {
26 // TODO Auto-generated catch block
27 e.printStackTrace();
28 }
29 return conn;
30
31 }
32
33 /**
34 * close 关闭数据库
35 * @param conn
36 * @param pstmt
37 * @param resu
38 */
39 public void close(Connection conn,PreparedStatement pstmt,ResultSet result){
40 if(conn != null){
41 try {
42 conn.close();
43 } catch (SQLException e) {
44 // TODO Auto-generated catch block
45 }
46 }
47 if(pstmt != null){
48 try {
49 pstmt.close();
50 } catch (SQLException e) {
51 // TODO Auto-generated catch block
52 e.printStackTrace();
53 }
54 }
55 if(result != null){
56 try {
57 result.close();
58 } catch (SQLException e) {
59 // TODO Auto-generated catch block
60 e.printStackTrace();
61 }
62 }
63 }
64
65 }
UserDao 类中的方法 getPage() 和方法 listUser() 分别用来计算总页数和查询指定页的数据，核心代码如下：
1 import java.sql.Connection;
2 import java.sql.PreparedStatement;
3 import java.sql.ResultSet;
4 import java.sql.SQLException;
5 import java.util.ArrayList;
6 import java.util.List;
7
8 import com.db.JDBCUtils;
9
10 public class UserDao {
11 /**
12 * 计算总的页数
13 * @return
14 */
15 public int getPage(){
16 int recordCount=0,t1=0,t2=0;
17 PreparedStatement pstmt=null;
18 ResultSet result=null;
19 JDBCUtils jdbc=new JDBCUtils();
20 Connection conn=jdbc.connect();
21 String sql="select count(*) from books";
22 try {
23 pstmt=conn.prepareStatement(sql);
24 result=pstmt.executeQuery();
25 result.next();
26 recordCount=result.getInt(1);
27 t1=recordCount%5;
28 t2=recordCount/5;
29 } catch (Exception e) {
30 // TODO Auto-generated catch block
31 e.printStackTrace();
32 }finally{
33 jdbc.close(conn, pstmt, result);
34 }
35 if(t1 != 0){
36 t2=t2+1;
37 }
38
39 return t2;
40 }
41
42 /**
43 * 查询指定页的数据
44 * @param pageNo
45 * @return
46 */
47 public List<User> listUser(int pageNo){
48 PreparedStatement pstmt=null;
49 ResultSet result=null;
50 List<User> list=new ArrayList<User>();
51 int pageSize=5;
52 int page=(pageNo-1)*5;
53 JDBCUtils jdbc=new JDBCUtils();
54 Connection conn=jdbc.connect();
55 String sql="select * from books order by id limit ?,?";
56 try {
57 pstmt=conn.prepareStatement(sql);
58 pstmt.setInt(1, page);
59 pstmt.setInt(2, pageSize);
60 result=pstmt.executeQuery();
61 while(result.next()){
62 User user=new User();
63 user.setId(result.getInt(1));
64 user.setName(result.getString(2));
65 user.setNumber(result.getString(3));
66 list.add(user);
67
68 }
69 } catch (Exception e) {
70 // TODO Auto-generated catch block
71 e.printStackTrace();
72 }finally{
73 jdbc.close(conn, pstmt, result);
74 }
75 return list;
76 }
77
78 }
User 类用于存储查询到的数据，核心代码如下：
1 public class User {
2 private int id;
3 private String name;
4 private String number;
5 public int getId() {
6 return id;
7 }
8 public void setId(int id) {
9 this.id = id;
10 }
11 public String getName() {
12 return name;
13 }
14 public void setName(String name) {
15 this.name = name;
16 }
17 public String getNumber() {
18 return number;
19 }
20 public void setNumber(String number) {
21 this.number = number;
22 }
23 }
2.控制层
ListUser 类内部调用 UserDao 对象查询数据并指派页面显示数据，核心代码如下：
1 import java.io.IOException;
2 import java.io.PrintWriter;
3 import java.util.ArrayList;
4 import java.util.List;
5
6 import javax.servlet.ServletException;
7 import javax.servlet.http.HttpServlet;
8 import javax.servlet.http.HttpServletRequest;
9 import javax.servlet.http.HttpServletResponse;
10
11 import com.dao.User;
12 import com.dao.UserDao;
13
14 public class ListUser extends HttpServlet {
15 public ListUser() {
16 super();
17 }
18
19 public void destroy() {
20 super.destroy(); // Just puts "destroy" string in log
21 // Put your code here
22 }
23
24 public void doGet(HttpServletRequest request, HttpServletResponse response)
25 throws ServletException, IOException {
26
27 doPost(request, response);
28 }
29
30 public void doPost(HttpServletRequest request, HttpServletResponse response)
31 throws ServletException, IOException {
32
33
34 response.setCharacterEncoding("utf-8");
35 int pageNo = 1;
36 UserDao userdao=new UserDao();
37 List<User> lists=new ArrayList<User>();
38 String pageno=request.getParameter("pageNos");
39 if(pageno != null){
40 pageNo=Integer.parseInt(pageno);
41 }
42 lists=userdao.listUser(pageNo);
43 int recordCount=userdao.getPage();
44 request.setAttribute("recordCount", userdao.getPage());
45 request.setAttribute("listss", lists);
46 request.setAttribute("pageNos", pageNo);
47 request.getRequestDispatcher("userlist.jsp").forward(request, response);
48 }
49
50 public void init() throws ServletException {
51 // Put your code here
52 }
53
54 }
3.表示层
输出页面 userlist.jsp ,使用 EL 和 JSTL 输出查询结果，核心代码如下：
1 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
2 <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
3 <%@ taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt"%>
4 <%@ taglib uri="http://java.sun.com/jsp/jstl/functions" prefix="fn"%>
5 <%
6 String path = request.getContextPath();
7 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
8 %>
9
10 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
11 <html>
12 <head>
13 <base href="<%=basePath%>">
14
15 <title>My JSP ‘userlist.jsp‘ starting page</title>
16
17 <meta http-equiv="pragma" content="no-cache">
18 <meta http-equiv="cache-control" content="no-cache">
19 <meta http-equiv="expires" content="0">
20 <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
21 <meta http-equiv="description" content="This is my page">
22 <!--
23 <link rel="stylesheet" type="text/css" href="styles.css">
24 -->
25 <style type="text/css">
26 th,td{width: 150px;border: 2px solid gray;text-align: center;}
27 body{text-align: center;}
28 a{text-decoration: none;}
29 table {border-collapse: collapse;}
30 </style>
31 </head>
32
33 <body>
34 <h2 align="center">图书信息</h2>
35 <table align="center">
36 <tr><td>书号</td><td>书名</td><td>库存量</td></tr>
37 </table>
38 <table align="center">
39 <c:forEach items="${listss}" var="person">
40 <tr>
41 <td class="hidden-480">${person.id}</td>
42 <td class="hidden-480">${person.name }</td>
43 <td class="hidden-480">${person.number }</td>
44 </tr>
45 </c:forEach>
46 </table>
47 <br>
48
49 <c:if test="${pageNos>1 }">
50 <a href="ListUser?pageNos=1" >首页</a>
51 <a href="ListUser?pageNos=${pageNos-1 }">上一页</a>
52 </c:if>
53
54 <c:if test="${pageNos <recordCount }">
55 <a href="ListUser?pageNos=${pageNos+1 }">下一页</a>
56 <a href="ListUser?pageNos=${recordCount }">末页</a>
57 </c:if>
58
59 <form action="ListUser">
60 <h4 align="center">共${recordCount}页  
61 <input type="text" value="${pageNos}" name="pageNos" size="1">页
62 <input type="submit" value="到达">
63 </h4>
64 </form>
65 </body>
66 </html>
4.效果图
时间： 2024-10-09 10:36:48