分页器，根据过来的参数计算当着页应当从哪一条记录开始显示，并且显示到哪。
PageUtils [pageSize=5, currIndex=1, totalCount=166, totalPage=34, startPosition=0]
PageUtils [pageSize=5, currIndex=5, totalCount=166, totalPage=34, startPosition=20]
PageUtils [pageSize=5, currIndex=34, totalCount=166, totalPage=34, startPosition=165]
PageUtils [pageSize=5, currIndex=1, totalCount=166, totalPage=34, startPosition=0]
PageUtils [pageSize=5, currIndex=9, totalCount=166, totalPage=34, startPosition=40]
PageUtils [pageSize=10, currIndex=9, totalCount=166, totalPage=17, startPosition=80]
package src;
public class TestPageUtils {
public static void main(String[] args) {
// TODO Auto-generated method stub
//假设一页显示5条，现在有166条
int pageSize = 5;
int totalCount = 166;
PageUtils pageUtils= new PageUtils(pageSize, totalCount);
System.out.println(pageUtils);
pageUtils.setCurrIndex(5);
System.out.println(pageUtils);
pageUtils.setCurrIndex(35);
System.out.println(pageUtils);
pageUtils.setCurrIndex(-1);
System.out.println(pageUtils);
pageUtils.setCurrIndex(9);
System.out.println(pageUtils);
pageUtils.setCurrIndex(9);
pageUtils.setPageSize(10);
System.out.println(pageUtils);
}
}
package src;
/**
*
* @lwd
* 分页工具类
*
*/
public class PageUtils {
//相关成员变量
// 页大小，每页显示多少条记录
private int pageSize;
//当前页
private int currIndex;
//总记录数
private int totalCount;
//总页数
private int totalPage;
//开始的记录开始的位置
private int startPosition;
//一页显示多少条和一共有多少条记录
public PageUtils(int pageSize, int totalCount) {
this.pageSize = pageSize;
this.totalCount = totalCount;
currIndex = 1;//默认显示第一页
startPosition = 0;//默认从第一条记录开始显示
int pages=totalCount/pageSize;
totalPage=totalCount%pageSize==0?pages:pages+1;
}
public int getPageSize() {
return pageSize;
}
public void setPageSize(int pageSize) {
this.pageSize = pageSize;
int pages=totalCount/pageSize;
totalPage=totalCount%this.pageSize==0?pages:pages+1;
startPosition=(currIndex-1)*pageSize;
}
public int getCurrIndex() {
return currIndex;
}
public void setCurrIndex(int currIndex) {
if(currIndex<1)
currIndex=1;
else if(currIndex>totalPage)
currIndex=totalPage;
this.currIndex = currIndex;
startPosition=(currIndex-1)*pageSize;
}
public int getTotalPage() {
return totalPage;
}
public int getStartPosition() {
return startPosition;
}
@Override
public String toString() {
return "PageUtils [pageSize=" + pageSize + ", currIndex=" + currIndex + ", totalCount=" + totalCount
+ ", totalPage=" + totalPage + ", startPosition=" + startPosition + "]";
}
}
JSP中调用。
<%@page import="src.PageUtils"%>
<%@page import="java.text.SimpleDateFormat"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%@ page import="
java.util.Date,
java.io.IOException,
java.io.PrintWriter,
java.sql.*
" %>
<%@ page import="src.User,src.Message"
%>
<%
Date date= new Date();
SimpleDateFormat df= new SimpleDateFormat("yyyy年MM月dd日 HH:mm:ss");
%>
<%!
//留言表共有多少条记录
int getTotalCount() throws Exception{
Class.forName("com.mysql.cj.jdbc.Driver");
Connection con = DriverManager.getConnection("jdbc:mysql://mysql.sqlpub.com:3306/huangjin","laocooon","fc12f7a5215e8e0a");
String sql = "SELECT COUNT(*) FROM message";
PreparedStatement pstmt = con.prepareStatement(sql);
//5.执行sql语句，并且接收结果
ResultSet rs = pstmt.executeQuery();
rs.next();
int res = rs.getInt(1);
rs.close();
pstmt.close();
con.close();
return res;
}
%>
<%
//获取page
String pages=request.getParameter("pages");
if(pages==null)
pages = "1";
int currIndex = Integer.parseInt(pages);
PageUtils pageUtils = new PageUtils(10,getTotalCount());//需要提供总记录数
pageUtils.setCurrIndex(currIndex);
out.println(pageUtils);
%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<link href="./css/1102.css" rel="stylesheet" type="text/css" />
<title>访客留言板</title>
</head>
<body>
<p>访客留言板</p>
<p><%="使用的浏览器是:<span style='font-size:16px;'>"+request.getHeader("User-Agent")+"</span>" %></p>
<p><%="使用的ip是:"+request.getRemoteAddr() %></p>
<p><%="现在时间是:"+ df.format(date) %></p>
<p><a href=./index.jsp?#form>我要留言</a></p>
<p>
<%
//读取message表中的所有记录
//1.导入jar包
//2.注册驱动
//Class.forName("com.mysql.jdbc.Driver");
Class.forName("com.mysql.cj.jdbc.Driver");
//3.获取连接
Connection con = DriverManager.getConnection("jdbc:mysql://mysql.sqlpub.com:3306/huangjin","laocooon","fc12f7a5215e8e0a");
//4.获取执行者对象
String sql = "SELECT * FROM message ORDER BY id DESC LIMIT ?,?";
PreparedStatement pstmt = con.prepareStatement(sql);
pstmt.setInt(1,pageUtils.getStartPosition());
pstmt.setInt(2,pageUtils.getPageSize());
//5.执行sql语句，并且接收结果
ResultSet rs = pstmt.executeQuery();
int i=pageUtils.getStartPosition()+1;
while(rs.next()){
String author=rs.getString(3);
String id=""+rs.getInt(1);
String message=rs.getString(2);
String posttime=rs.getString(4);
out.println("<div class='div1'>");
out.println("<p id='p1'>作者:" + author + "</p>");
out.println("<p id='p2'>#" + i++ + "</p>");
out.println("<p id='p3'>" + message + "</p>");
out.println("<p id='p4'>发布日期:" + posttime + "</p>");
out.println("<p id='p5'><a href='./index.jsp?id=" + id + "#form'>回复</a></p> ");
out.println("</div>");
out.println("<br><br> ");
}
rs.close();
pstmt.close();
con.close();
%>
<br>
<div style="text-align: right;">
[一页<%=pageUtils.getPageSize() %>个]
<a href="index.jsp?pages=1">第一页</a>
<a href="index.jsp?pages=<%=pageUtils.getCurrIndex()-1%>">上一页</a>
<a href="index.jsp?pages=<%=pageUtils.getCurrIndex()+1%>">下一页</a>
<a href="index.jsp?pages=<%=pageUtils.getTotalPage()%>">最后页</a>
</div>
<br>
<form action='doadd.jsp' method='get'>
<a id="form"> 用 户 名:</a>
<input type=text required name=you placeholder=请输入你的姓名 /><br><br>
<%
String id=request.getParameter("id");
if(id==null){
out.println("留言信息:<textarea rows=4 cols=60 required name=text placeholder=留言处></textarea><br>");
}
else{
out.println("留言信息:<textarea rows=4 cols=60 required name=text placeholder=留言处>回复#"+ id +":</textarea><br>");
}
%>
<input type='submit'> <input type='reset'>
</form>
</body>
</html>
