java web 简单的分页显示

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：

 import java.sql.Connection;
 import java.sql.DriverManager;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;
 import java.sql.SQLException;

 public class JDBCUtils {
     private Connection conn=null;
     private PreparedStatement pstmt=null; 

     /**
      * connect 连接数据库
      * @return
      */
     public Connection connect(){
         String user="root";
         String password="1234";
         String driverClass = "com.mysql.jdbc.Driver";
         String jdbcUrl = "jdbc:mysql://localhost:3306/book";

         try {
             Class.forName(driverClass);
             conn = DriverManager.getConnection(jdbcUrl, user, password);
         } catch (Exception e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }
         return conn;

     }

     /**
      * close 关闭数据库
      * @param conn
      * @param pstmt
      * @param resu
      */
     public void close(Connection conn,PreparedStatement pstmt,ResultSet result){
         if(conn != null){
             try {
                 conn.close();
             } catch (SQLException e) {
                 // TODO Auto-generated catch block
             }
         }
         if(pstmt != null){
             try {
                 pstmt.close();
             } catch (SQLException e) {
                 // TODO Auto-generated catch block
                 e.printStackTrace();
             }
         }
         if(result != null){
             try {
                 result.close();
             } catch (SQLException e) {
                 // TODO Auto-generated catch block
                 e.printStackTrace();
             }
         }
     }

 }

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：

 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 com.db.JDBCUtils;

 public class UserDao {
     /**
      * 计算总的页数
      * @return
      */
     public int getPage(){
         int recordCount=0,t1=0,t2=0;
         PreparedStatement pstmt=null;
         ResultSet result=null;
         JDBCUtils jdbc=new JDBCUtils();
         Connection conn=jdbc.connect();
         String sql="select count(*) from books";
         try {
             pstmt=conn.prepareStatement(sql);
             result=pstmt.executeQuery();
             result.next();
             recordCount=result.getInt(1);
             t1=recordCount%5;
             t2=recordCount/5;
         } catch (Exception e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }finally{
             jdbc.close(conn, pstmt, result);
         }
         if(t1 != 0){
             t2=t2+1;
         }

         return t2;
     }

     /**
      * 查询指定页的数据
      * @param pageNo
      * @return
      */
     public List<User> listUser(int pageNo){
         PreparedStatement pstmt=null;
         ResultSet result=null;
         List<User> list=new ArrayList<User>();
         int pageSize=5;
         int page=(pageNo-1)*5;
         JDBCUtils jdbc=new JDBCUtils();
         Connection conn=jdbc.connect();
         String sql="select * from books order by id limit ?,?";
         try {
             pstmt=conn.prepareStatement(sql);
             pstmt.setInt(1, page);
             pstmt.setInt(2, pageSize);
             result=pstmt.executeQuery();
             while(result.next()){
                 User user=new User();
                 user.setId(result.getInt(1));
                 user.setName(result.getString(2));
                 user.setNumber(result.getString(3));
                 list.add(user);

             }
         } catch (Exception e) {
             // TODO Auto-generated catch block
             e.printStackTrace();
         }finally{
             jdbc.close(conn, pstmt, result);
         }
         return list;
     }

 }

User 类用于存储查询到的数据，核心代码如下：

 public class User {
     private int id;
     private String name;
     private String number;
     public int getId() {
         return id;
     }
     public void setId(int id) {
         this.id = id;
     }
     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }
     public String getNumber() {
         return number;
     }
     public void setNumber(String number) {
         this.number = number;
     }
 }

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：

 import java.io.IOException;
 import java.io.PrintWriter;
 import java.util.ArrayList;
 import java.util.List;

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

 import com.dao.User;
 import com.dao.UserDao;

 public class ListUser extends HttpServlet {
     public ListUser() {
         super();
     }

     public void destroy() {
         super.destroy(); // Just puts "destroy" string in log
         // Put your code here
     }

     public void doGet(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {

         doPost(request, response);
     }

     public void doPost(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {

         response.setCharacterEncoding("utf-8");
         int pageNo = 1;
         UserDao userdao=new UserDao();
         List<User> lists=new ArrayList<User>();
         String pageno=request.getParameter("pageNos");
         if(pageno != null){
             pageNo=Integer.parseInt(pageno);
         }
         lists=userdao.listUser(pageNo);
         int recordCount=userdao.getPage();
         request.setAttribute("recordCount", userdao.getPage());
         request.setAttribute("listss", lists);
         request.setAttribute("pageNos", pageNo);
         request.getRequestDispatcher("userlist.jsp").forward(request, response);
     }

     public void init() throws ServletException {
         // Put your code here
     }

 }

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：

 <%@ page language="java" import="java.util.*"  pageEncoding="UTF-8"%>
 <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
 <%@ taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt"%>
 <%@ taglib uri="http://java.sun.com/jsp/jstl/functions" prefix="fn"%>
 <%
 String path = request.getContextPath();
 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
 %>

 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
 <html>
   <head>
     <base href="<%=basePath%>">

     <title>My JSP 'userlist.jsp' starting page</title>

     <meta http-equiv="pragma" content="no-cache">
     <meta http-equiv="cache-control" content="no-cache">
     <meta http-equiv="expires" content="0">
     <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
     <meta http-equiv="description" content="This is my page">
     <!--
     <link rel="stylesheet" type="text/css" href="styles.css">
     -->
 <style type="text/css">
 th,td{width: 150px;border: 2px solid gray;text-align: center;}
 body{text-align: center;}
 a{text-decoration: none;}
 table {border-collapse: collapse;}
 </style>
   </head>

   <body>
     <h2 align="center">图书信息</h2>
     <table align="center">
         <tr><td>书号</td><td>书名</td><td>库存量</td></tr>
     </table>
      <table align="center">
          <c:forEach items="${listss}" var="person">
          <tr>
          <td class="hidden-480">${person.id}</td>
          <td class="hidden-480">${person.name }</td>
          <td class="hidden-480">${person.number }</td>
          </tr>
         </c:forEach>
     </table>
      <br>

      <c:if test="${pageNos>1 }">
          <a href="ListUser?pageNos=1" >首页</a>
          <a href="ListUser?pageNos=${pageNos-1 }">上一页</a>
      </c:if>

       <c:if test="${pageNos <recordCount }">
          <a href="ListUser?pageNos=${pageNos+1 }">下一页</a>
          <a href="ListUser?pageNos=${recordCount }">末页</a>
      </c:if>

     <form action="ListUser">
     <h4 align="center">共${recordCount}页 &nbsp
     <input type="text" value="${pageNos}" name="pageNos" size="1">页
     <input type="submit" value="到达">
     </h4>
      </form>
   </body>
 </html>

4.效果图