分页探究--Filter+JSTL

　　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 stubss = 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 hereString 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 chainSystem.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;}}