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{ 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