分页探究--Filter+JSTL

时间：2022-05-28 17:06:00

　　最近卡了一个功能就是分页，查了很多资料，分页大概是两种类型：一种是把数据库的东西全部查出来然后放在session里，用list一页一页传到页面，这样的消耗比较大;另一种就是使用sql语句的limit来进行数据库分页查询。我使用的是后者。

　　大致逻辑： (1)需要currentPage，count属性。

　　　　　　 　(2)需要注意current不能点击。

　　　　　　　 (3)全使用a标签进行页面跳转。并附上请求页码。

　　　　　　　 (4)初始化查询0页，并用filter装入list中，在页面显示的时候方便遍历。

　　　　　　　 (5)过程：页面加载->filter查询初始数据装入request->页面遍历并计算出页码请求附带在url后->请求发出后filter使用getParameter获得页码对数据库进行查询，并装入list中->页面加载的时候遍历list出现新数据。

　　页面如下：

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>

<%@page contentType="text/html; charset=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>分页列表</title>

</head>

<body>

<center>

    <%

        int currenPage=((Integer)request.getAttribute("currenPage")).intValue();

        int count=((Integer)request.getAttribute("count")).intValue();

    %>

    <table border="1px">

        <tr>

            <td>ID</td>

            <td>用户名</td>

            <td>性别</td>

            <td>年龄</td>

        </tr>

        <c:forEach var="usr" items="${list}">

        <tr>

            <td>${usr.id}</td>

            <td>${usr.name}</td>

            <td>${usr.sex}</td>

            <td>${usr.age}</td>

        </tr>

        </c:forEach>

    </table>

    <%

        int prePage=currenPage-1;

        if(currenPage==1)

            prePage=currenPage;

    %>

    <a href="Demo2.jsp?<%="curren="+prePage%>">上一页</a>

    <%

        int i=1;

        int end=currenPage+5;

        if(currenPage>5){

            i=currenPage-5;

        }

        if(end>count/10){

            end=count/10;

            System.out.println("end="+end);

        }

        for(;i<=end;i++)

        {

            System.out.println("i="+i);

            if(i == (currenPage)){

        %>

        [<%=currenPage%>]

        <%

            }else{

        %>

            <a href="Demo2.jsp?<%="curren="+i%>"><%=i%></a>

        <%

            }

        }

        %>

        <%

            int nextPage=currenPage+1;

            if(nextPage>count/10)

                nextPage--;

        %>

    <a href="Demo2.jsp?<%="curren="+nextPage%>">下一页</a> 

</center>

</body>

</html>

　　Filter如下

package filter;

import java.io.IOException;

import java.util.List;

import javax.servlet.Filter;

import javax.servlet.FilterChain;

import javax.servlet.FilterConfig;

import javax.servlet.ServletException;

import javax.servlet.ServletRequest;

import javax.servlet.ServletResponse;

import javax.servlet.annotation.WebFilter;

import dividedpage.SelectService;

import model.test_u;

/**

 * Servlet Filter implementation class divideFilter

 */

@WebFilter("/Demo2.jsp")

public class divideFilter implements Filter {

    private static final long serialVersionUID = 1L;

    private int start=0;

    private int size=10;

    private SelectService ss;

    private List<test_u> list;

    /**

     * Default constructor.

     */

    public divideFilter() {

        // TODO Auto-generated constructor stub

        ss = new SelectService();

    }

    /**

     * @see Filter#destroy()

     */

    public void destroy() {

        // TODO Auto-generated method stub

    }

    /**

     * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)

     */

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {

        // TODO Auto-generated method stub

        // place your code here

        String cu=request.getParameter("curren");

        if(cu!=null){

            start=Integer.parseInt(cu);

        }

        System.out.println(start);

        list = ss.selectLimit((start-1)*size, size);

        int count = ss.getConut();

        request.setAttribute("list", list);

        request.setAttribute("count", count);

        request.setAttribute("currenPage", start);

        // pass the request along the filter chain

        System.out.println("执行过滤");

        chain.doFilter(request, response);

    }

    /**

     * @see Filter#init(FilterConfig)

     */

    public void init(FilterConfig fConfig) throws ServletException {

        // TODO Auto-generated method stub

    }

}

　　JDBC如下

package DAO;

import java.sql.*;

public class Connect2DB {

    String  driver="com.mysql.jdbc.Driver";

    Connection con;

    String url="jdbc:mysql://localhost:3306/MyData";

    String user="root";

    String pwd="qwert123";

    public Connect2DB(){

        connection2MYSQL() ;

    }

    public void connection2MYSQL()

    {

        try {

            Class.forName(driver);  

            con=DriverManager.getConnection(url,user,pwd);  

            if(!con.isClosed())

                System.out.println("连接成功");  

        } catch (Exception e) {

            e.printStackTrace();

        }                  

    }

    public Connection getConn(){

        return con;

    }

}
package 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 model.test_u;

public class OperatorDB {

    private Connection con;

    public OperatorDB(){

        con=new Connect2DB().getConn();

    }

    public void addUser(test_u u){

        String sql="insert into test_u(id,name,sex,age) values(?,?,?,?)";

        PreparedStatement ps;

        try {

            ps=con.prepareStatement(sql);

            ps.setInt(1, u.getId());

            ps.setString(2, u.getName());

            ps.setString(3, u.getSex());

            ps.setString(4, u.getAge());

            ps.executeUpdate();

        } catch (SQLException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }

    }

    public void delUserById(int id){

        String sql="delete from test_u where stu_id = ?";

        PreparedStatement ps;

        try {

            ps=con.prepareStatement(sql);

            ps.setInt(1, id);

            ps.executeUpdate();

        } catch (SQLException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }

    }

    public List<test_u> selectLimit(int start,int size){

         String sql = "select * from test_u limit ?,?";

         List<test_u> result=new ArrayList<test_u>();

         PreparedStatement ps;

        try {

            ps = con.prepareStatement(sql);

            ps.setInt(1, start);

            ps.setInt(2, size);

            ResultSet rs = ps.executeQuery();

            while(rs.next()){

                int id=rs.getInt("id");

                String name=rs.getString("name");

                String sex=rs.getString("sex");

                String age=rs.getString("age");

                test_u t=new test_u(id,name,sex,age);

                result.add(t);

            }

        } catch (SQLException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }

         return result;

    }

    public int getCount(){

        String sql="SELECT COUNT(*) FROM test_u";

        int rowCount = 0;

        try {

            PreparedStatement ps;

            ps = con.prepareStatement(sql);

            ResultSet rs = ps.executeQuery(sql);

            rs.next();

            rowCount = rs.getInt(1);

        } catch (SQLException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }      

        return rowCount;

    }

    public void close(){

        try {

            if(!con.isClosed())

                con.close();

        } catch (SQLException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }

    }

}

　　Service如下

package dividedpage;

import java.util.List;

import DAO.OperatorDB;

import model.test_u;

public class SelectService {

    public List<test_u> selectLimit(int start,int size){

        OperatorDB odb=new OperatorDB();

        List<test_u> list=odb.selectLimit(start, size);

        odb.close();

        return list;

    }

    public int getConut(){

        OperatorDB odb=new OperatorDB();

        int count = odb.getCount();

        odb.close();

        return count;

    }

}

　　Bean如下

package model;

public class test_u {

    private int id;

    private String name;

    private String sex;

    private String age;

    public test_u(){

    }

    public test_u(int id, String name, String sex, String age) {

        super();

        this.id = id;

        this.name = name;

        this.sex = sex;

        this.age = age;

    }

    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 getSex() {

        return sex;

    }

    public void setSex(String sex) {

        this.sex = sex;

    }

    public String getAge() {

        return age;

    }

    public void setAge(String age) {

        this.age = age;

    }

}

　　数据表如下，插入100条记录

分页探究--Filter+JSTL

　　感觉代码很冗余，页面不够干净，不过也训练了分页的思想。

分页探究--Filter+JSTL

　　下列标签栏全是a标签，上一页current-1，下一页current+1；需要注意页面边界（最大，最小页）。查询limit大概是（（current-1）*size，size）这样的公式。

　　目录树如下：

分页探究--Filter+JSTL

　　JSTL需要下载个jar包，很容易找到，添加他们进path就好。

分页探究--Filter+JSTL

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