分页探究--Filter+JSTL

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2024-08-11 11:37:07 211人阅读

　　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;    }    }