数据的分页处理

当页面中要显示的内容过多需要分多页显示、或是数据量过大内存吃不消时，需要分页处理。

原理：每次从数据库中取出一定量的数据，通过jsp页面显示

实现：

①写一个类封装分页的页面

②从数据库中取出一个页面的数据，将信息封装到分页页面对象中

③根据情况，将分页的页面对象设置到request对象、session对象或servletContext对象属性中，供jsp页面调用

④在jsp页面中显示分页数据、分页页码、上一页下一页、跳转页面等

下面看具体代码:

分页页面Page类：

package cn.wzbrilliant.domain;

import java.util.List;

//界面上所有与分页有关的都找此类要
public class Page {
    private List records;
    private int pagesize = 10;//每页显示的记录条数
    private int pagenum;//用户要看的页码即当前页码
    private int totalpage;//总页数
    private int startIndex;//每页开始记录的索引
    private int totalrecords;//总记录条数

    //显示的页码
    private int startPage;
    private int endPage;

    public Page(int pagenum,int totalrecords){
        this.pagenum = pagenum;
        this.totalrecords = totalrecords;

        //计算每页开始记录的索引
        startIndex = (pagenum-1)*pagesize;
        //计算总页数
        totalpage = totalrecords%pagesize==0?totalrecords/pagesize:(totalrecords/pagesize+1);

        //显示的页码
        if(totalpage<=9){
            startPage = 1;
            endPage = totalpage;
        }else{
            startPage = pagenum-4;
            endPage = pagenum+4;
            if(startPage<1){
                startPage = 1;
                endPage = 9;
            }
            if(endPage>totalpage){
                endPage = totalpage;
                startPage = totalpage-8;
            }
        }
    }

    public List getRecords() {
        return records;
    }

    public void setRecords(List records) {
        this.records = records;
    }

    public int getPagesize() {
        return pagesize;
    }

    public void setPagesize(int pagesize) {
        this.pagesize = pagesize;
    }
    public int getPagenum() {
        return pagenum;
    }

    public void setPagenum(int pagenum) {
        this.pagenum = pagenum;
    }

    public int getTotalpage() {
        return totalpage;
    }

    public void setTotalpage(int totalpage) {
        this.totalpage = totalpage;
    }

    public int getStartIndex() {
        return startIndex;
    }
    public void setStartIndex(int startIndex) {
        this.startIndex = startIndex;
    }

    public int getTotalrecords() {
        return totalrecords;
    }

    public void setTotalrecords(int totalrecords) {
        this.totalrecords = totalrecords;
    }

    public int getStartPage() {
        return startPage;
    }

    public void setStartPage(int startPage) {
        this.startPage = startPage;
    }

    public int getEndPage() {
        return endPage;
    }

    public void setEndPage(int endPage) {
        this.endPage = endPage;
    }

}

从数据库中取出一定条数的记录，此处以mysql为例，sql语句为 select * from 表名 limit ?,? 两个问号分别为起始位置和结束位置

在jsp页面中显示分页页码、上一页下一页、跳转页面等的实现代码：

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!-- 分页的部分 -->
 第${page.pagenum}页/共${page.totalpage}页  
 <a href="${pageContext.request.contextPath}/servlet/ShowAllMessageServlet">首页</a>  
 <a href="${pageContext.request.contextPath}/servlet/ShowAllMessageServlet?pagenum=${page.pagenum-1==0?1:page.pagenum-1}">上一页</a>  
      <c:forEach begin="${page.startPage}" end="${page.endPage}" var="num">
            <a href="${pageContext.request.contextPath}/servlet/ShowAllMessageServlet?pagenum=${num}">${num }</a>
      </c:forEach>

    <a href="${pageContext.request.contextPath}/servlet/ShowAllMessageServlet?pagenum=${page.pagenum+1>page.totalpage?page.totalpage:page.pagenum+1}">下一页</a>  
    <a href="${pageContext.request.contextPath}/servlet/ShowAllMessageServlet?pagenum=${page.totalpage}">尾页</a>
    <select id="s1">
          <c:forEach begin="1" end="${page.totalpage}" var="num">
                 <option value="${num}" ${page.pagenum==num?'selected="selected"':''}>${num}</option>
          </c:forEach>
     </select>
     <a href="javascript:jump()">跳转</a>

<script type="text/javascript">
      function jump(){
            var num = document.getElementById("s1").value;
            window.location.href="${pageContext.request.contextPath}/servlet/ShowAllMessageServlet?pagenum="+num;
      }
</script>

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