①分页效果：
②分页PageBean模型设计
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package com.cn.utils;
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import java.util.List;
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public class PageBean<T> {
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/**
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* 供外界调用，只能传入一下参数
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* @param currentPageNumber 要显示的当前页码
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* @param totalRecordCounts 总记录条数
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* @param pageSize 每页显示条数
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*/
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public PageBean(int currentPageNumber, int totalRecordCounts, int pageSize){
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this.currentPageNumber = currentPageNumber;
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this.totalRecordCounts = totalRecordCounts;
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this.pageSize = pageSize;
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//计算总页数
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totalPageCounts = totalRecordCounts%pageSize==0?totalRecordCounts/pageSize:(totalRecordCounts/pageSize+1);
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//计算每页开始的索引值
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startIndex = (currentPageNumber-1)*pageSize;
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/**
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* 计算显示的开始页码和显示的结束页码
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*/
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/**
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* 注意设置变量，设置分页显示时显示的最大页码数量，这个数字必须为奇数，为了让当前页居中
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*/
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int maxShowPageNum = 5;//可自由设置（为奇数即可）
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if(totalPageCounts <= maxShowPageNum){//总页数<=maxShowPageNum
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beginPageNumber = 1;
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endPageNumber = totalPageCounts;
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}else{//总页数>=maxShowPageNum
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beginPageNumber = currentPageNumber-maxShowPageNum/2;//假如maxShowPageNum=5，这是候当前页居中，则左右两边为当前页+maxShowPageNum/2
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endPageNumber = currentPageNumber+maxShowPageNum/2;
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if(beginPageNumber < 1){
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beginPageNumber = 1;
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endPageNumber = maxShowPageNum;
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}
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if(endPageNumber > totalPageCounts){
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beginPageNumber = totalPageCounts-(maxShowPageNum-1);
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endPageNumber = totalPageCounts;
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}
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}
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}
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/**
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* 要显示的当前页码
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*/
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private int currentPageNumber;
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/**
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* 记录总条数
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*/
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private int totalRecordCounts;
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/**
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* 每页显示数据条数
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*/
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private int pageSize;
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/**
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* 总页数
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*/
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private int totalPageCounts;
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/**
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* 每页开始的索引
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*/
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private int startIndex;
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/**
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* 分页查询的数据
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*/
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private List<T> pageList;
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/**
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* 页码显示的起始页
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*/
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private int beginPageNumber;
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/**
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* 页码显示的结束码
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*/
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private int endPageNumber;
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/**
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* 设置分页跳转路径
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*/
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private String pageUri;
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public String getPageUri() {
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return pageUri;
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}
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public void setPageUri(String pageUri) {
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this.pageUri = pageUri;
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}
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public int getBeginPageNumber() {
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return beginPageNumber;
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}
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public void setBeginPageNumber(int beginPageNumber) {
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this.beginPageNumber = beginPageNumber;
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}
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public int getEndPageNumber() {
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return endPageNumber;
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}
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public void setEndPageNumber(int endPageNumber) {
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this.endPageNumber = endPageNumber;
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}
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public int getCurrentPageNumber() {
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return currentPageNumber;
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}
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public void setCurrentPageNumber(int currentPageNumber) {
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this.currentPageNumber = currentPageNumber;
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}
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public int getTotalRecordCounts() {
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return totalRecordCounts;
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}
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public void setTotalRecordCounts(int totalRecordCounts) {
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this.totalRecordCounts = totalRecordCounts;
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}
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public int getPageSize() {
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return pageSize;
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}
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public void setPageSize(int pageSize) {
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this.pageSize = pageSize;
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}
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public int getTotalPageCounts() {
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return totalPageCounts;
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}
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public void setTotalPageCounts(int totalPageCounts) {
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this.totalPageCounts = totalPageCounts;
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}
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public int getStartIndex() {
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return startIndex;
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}
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public void setStartIndex(int startIndex) {
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this.startIndex = startIndex;
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}
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public List<T> getPageList() {
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return pageList;
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}
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public void setPageList(List<T> pageList) {
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this.pageList = pageList;
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}
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}
③Page.jsp公用分页页面
（使用方法：在要分页的页面利用<%@ include file" " %>静态包含此页面，注意此分页跳转链接中带了“分页条件，根据自己“分页条件需求”作出更改即可）
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<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
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<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
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<!-- 如果查询出的数据总条数为0，则不显示分页 -->
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<c:if test="${not empty pb.totalPageCounts }">
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<!-- 如果当前页为1，则不显示首页，否则显示首页 -->
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<a href="${pageContext.request.contextPath }${pb.pageUri }¤tPageNumber=1&categoryId=${sessionScope.categoryId}">${pb.currentPageNumber==1?"":"首页" }</a>
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<!-- 如果当前页为1，则不显示上一页，否则显示上一页 -->
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<a href="${pageContext.request.contextPath }${pb.pageUri }¤tPageNumber=${(pb.currentPageNumber-1)<=0?1:pb.currentPageNumber-1}&categoryId=${sessionScope.categoryId}">${pb.currentPageNumber==1?'':'上一页' }</a>
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<!-- 若左端还有页码，则显示省略号，有上一页功能 -->
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<c:if test="${pb.beginPageNumber>1 }">
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<a href="${pageContext.request.contextPath }${pb.pageUri }¤tPageNumber=${pb.currentPageNumber-1}&categoryId=${sessionScope.categoryId}" style="text-decoration: none;"><strong>... </strong></a>
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</c:if>
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<!-- 显示数字页码，当前页数字显示红色 -->
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<c:forEach begin="${pb.beginPageNumber }" end="${pb.endPageNumber }" var="count">
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<a href="${pageContext.request.contextPath }${pb.pageUri }¤tPageNumber=${count}&categoryId=${sessionScope.categoryId}"><span style="${pb.currentPageNumber==count?'color:red':''}">${count }</span></a>
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</c:forEach>
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<!-- 若右端还有页码，则显示省略号 ，有下一页功能 -->
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<c:if test="${pb.endPageNumber<pb.totalPageCounts }">
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<a href="${pageContext.request.contextPath }${pb.pageUri }¤tPageNumber=${pb.currentPageNumber+1}&categoryId=${sessionScope.categoryId}" style="text-decoration: none;"><strong>... </strong></a>
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</c:if>
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<!-- 如果当前页为总页数，则不显示下一页，否则显示下一页 -->
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<a href="${pageContext.request.contextPath }${pb.pageUri }¤tPageNumber=${(pb.currentPageNumber+1)>pb.totalPageCounts?pb.totalPageCounts:pb.currentPageNumber+1}&categoryId=${sessionScope.categoryId}">${pb.currentPageNumber==pb.totalPageCounts?'':'下一页' }</a>
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<!-- 如果当前页为总页数，则不显示尾页，否则显示尾页 -->
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<a href="${pageContext.request.contextPath }${pb.pageUri }¤tPageNumber=${pb.totalPageCounts }&categoryId=${sessionScope.categoryId}">${pb.currentPageNumber==pb.totalPageCounts?'':'尾页' }</a>
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<!-- 输入框只能输入不为0的数字，为空或者为不存在的页码则还是显示当前页 -->
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<input type="text" id="jumpPageNum" size="1" onkeyup="if(this.value.length==1){this.value=this.value.replace(/[^1-9]/g,'')}else{this.value=this.value.replace(/\D/g,'')}" onafterpaste="if(this.value.length==1){this.value=this.value.replace(/[^1-9]/g,'')}else{this.value=this.value.replace(/\D/g,'')}"/> <a href="#" onclick="jumpPageNum(this);">跳转</a>
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当前第<span style="color:red">${pb.currentPageNumber }</span>页/共<span style="color:red">${pb.totalPageCounts }</span>页 <span style="color:red">${pb.totalRecordCounts }</span>条数据
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<!-- 改变每页显示的数据条数 -->
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每页显示<select name="pageSize" onchange="changePageSize(this)">
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<option value="5" ${sessionScope.pageSize==5?"selected='selected'":"" }>5</option>
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<option value="10" ${sessionScope.pageSize==10?"selected='selected'":"" }>10</option>
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<option value="15" ${sessionScope.pageSize==15?"selected='selected'":"" }>15</option>
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</select>条数据
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</c:if>
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<script type="text/javascript">
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//跳转框输入数字，跳转时调用
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function jumpPageNum(node){
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var jumpPageNum = document.getElementById("jumpPageNum").value;
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if(jumpPageNum==null || jumpPageNum==""){//如果没有输入跳转页
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jumpPageNum = "${pb.currentPageNumber}";//保持当前页
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}
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var totalPageCounts = "${pb.totalPageCounts}";
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if(jumpPageNum<=0){
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jumpPageNum = "${pb.currentPageNumber}";//保持当前页
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}
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/*注意js中
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①数字和字符串比较：javascript都会把字符串转换成数字，然后按照数字顺序比较它们。
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②字符串与字符串的比较：
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情况1：能找到对应位置上的不同字符，那么就比较第一个不同字符的大小。
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情况2：不能找到对应位置上的不同字符，这时候比较的是两个字符串的长度。
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*/
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if(parseInt(jumpPageNum)>parseInt(totalPageCounts)){//这里需要将字符串转换成数字，才能正确比较
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jumpPageNum = "${pb.currentPageNumber}";//保持当前页
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}
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node.href = "${pageContext.request.contextPath }${pb.pageUri }&categoryId=${sessionScope.categoryId}¤tPageNumber="+jumpPageNum;
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}
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//改变每页显示的数据条数
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function changePageSize(node){
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var pageSize = node.value;
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//注意每次改变每页显示数据条数，当前页不能作为参数代入，只要更改了每页显示条数，就必须从第一页查起，因为假如之前当前页是第5页，这样数据库查询时起始索引为（当前页-1）*每页显示条数，若结果过大，这样很可能查询不到数据。
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window.location.href="${pageContext.request.contextPath }${pb.pageUri }&categoryId=${sessionScope.categoryId}&pageSize="+pageSize;
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}
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</script>
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④分页Servlet
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/**
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* 根据图书种类分页查询图书
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* @param request
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* @param response
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* @return
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*/
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public Object showBooksByCategory(HttpServletRequest request, HttpServletResponse response){
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//获取请求参数分类id
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String categoryId = request.getParameter("categoryId");
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String categoryIdSession = (String)request.getSession().getAttribute("categoryId");
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if(categoryId == null || categoryId == "" || categoryId.hashCode()==0){//说明是首页进入
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categoryIdSession = null;//注意这里必须清空，当session中有categoryId时，categoryIdSession!=null, 页面点击首页时，categoryId==null，但是下面传入的是categoryIdSession的不为空值按分类查询
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request.getSession().removeAttribute("categoryId");
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}else{//说明是处在分类
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categoryIdSession = categoryId;
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request.getSession().setAttribute("categoryId", categoryIdSession);//更改session中的值
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}
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//获取页面传递过来的要显示的当前页码
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String currentPageNumber = request.getParameter("currentPageNumber");
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//获取页面传递过来的要每页显示的条数
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String pageSize = request.getParameter("pageSize");
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//获取session中pageSize的值
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String pageSizeSession = (String)request.getSession().getAttribute("pageSize");
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/**
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* 首先判Session中是否有pageSize，没有则创建，默认值10
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* 再判断页面传递过来的pageSize是否为null
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* 1.如果为null 说明页面没有更改每页显示条数的需求
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* 分页时，取session中的pageSize值，供分页使用
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* 2.如果不为null 说明需要更改每页显示条数
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* 则把session中的pageSize改为页面传递过来的值大小，供分页使用
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*/
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if(pageSizeSession == null){
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pageSizeSession = "10";//设置session中pageSize值为10，即默认每页显示10条
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request.getSession().setAttribute("pageSize", pageSizeSession);
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}
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if(pageSize != null){
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pageSizeSession = pageSize;
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request.getSession().setAttribute("pageSize", pageSizeSession);//更改session中的值
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}
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//调用service查询所有的图书
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PageBean<Book> pb = bs.findPageBooksByCategory(currentPageNumber, categoryIdSession, pageSizeSession);
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//设置分页页码跳转时的uri
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pb.setPageUri("/servlet/AppServlet?method=showBooksByCategory");
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request.setAttribute("pb", pb);
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return request.getRequestDispatcher("/app/welcome.jsp");
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}
⑤分页Service
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@Override
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public PageBean<Book> findPageBooksByCategory(String currentPageNumber,
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String categoryId, String pageSize) {
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/**
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* 设置当前页页码
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*/
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int number = 1;//默认为第一页
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//判断要显示的当前页码
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if(currentPageNumber!=null && !"".equals(currentPageNumber)){
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number = Integer.valueOf(currentPageNumber);
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}
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int totalRecordCounts = 0;
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if(categoryId==null || categoryId=="" || categoryId.hashCode()==0){//不按分类
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//根据获取所有书总记录数
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totalRecordCounts = bDao.getTotalRecordCounts();
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}else{
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//根据图书种类，获取记录数
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totalRecordCounts = bDao.getTotalRecordCounts(categoryId);
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}
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//创建PageBean对象
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PageBean<Book> pb = new PageBean<Book>(number, totalRecordCounts, Integer.valueOf(pageSize));
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//调用dao,按图书种类获取图书
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List<Book> bs = null;
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//TODO 分析 == null || =="" 和 ！=null && !=""
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if(categoryId==null || categoryId=="" || categoryId.hashCode()==0){//不按分类
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bs = bDao.findPageBooks(pb.getStartIndex(), pb.getPageSize());
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}else{
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bs = bDao.findPageBooksByCategory(pb.getStartIndex(), pb.getPageSize(), categoryId);
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}
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//封装到PageBean对象中
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pb.setPageList(bs);
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return pb;
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}
⑥分页Dao
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@Override
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public int getTotalRecordCounts(String categoryId) {
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try{
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//sql语句
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String sql = "select count(*) from book where category_id = ?";
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return qr.query(sql, new ScalarHandler<Long>(), categoryId).intValue();
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}catch(Exception e){
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throw new DaoRuntimeException(e);
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}
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}
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@Override
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public List<Book> findPageBooksByCategory(int startIndex, int pageSize,
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String categoryId) {
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try{
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//sql语句
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String sql = "select id, bName, author, price, image, bDescription, category_id from book where category_id = ? limit ?, ?";
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return qr.query(sql, new BeanListHandler<Book>(Book.class), categoryId, startIndex, pageSize);
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}catch(Exception e){
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throw new DaoRuntimeException(e);
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}
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}