在進(jìn)行web應(yīng)用開發(fā)的時(shí)候經(jīng)常要進(jìn)行分頁處理，經(jīng)常看到一些人在問分頁處理的問題，現(xiàn)在我把自己的處理方法寫在這兒，希望能對(duì)需要進(jìn)行分頁處理的朋友有所幫助。
一、在struts中分頁有兩種結(jié)構(gòu)：
??? 1. 在Action中通過DAO查詢出所有的記錄，然后加到session或request對(duì)象中，傳到客戶端，由JSP進(jìn)行分頁。這種方法對(duì)于在數(shù)據(jù)量少的時(shí)候很方便，也不影響速度。
??? 2.在Action中每次通過DAO只查詢出一頁的記錄，再傳給JSP頁面。這種結(jié)構(gòu)對(duì)于數(shù)據(jù)量大的程序很好，但對(duì)于數(shù)據(jù)量小的情況，會(huì)增加對(duì)服務(wù)器的請(qǐng)求，加大服務(wù)器的負(fù)載。
?????
二、Hibernate查詢
??? 由于在Hibernate中直接提供了對(duì)數(shù)據(jù)庫定點(diǎn)定量的查詢方法，所以我采用的是第2種方法。
如：
從第1萬條開始取出100條記錄
Query q = session.createQuery("from Cat as c");
q.setFirstResult(10000);
q.setMaxResults(100);
List l = q.list();
三、具體實(shí)現(xiàn)
?1.Pager類
package com.jpcf.db.helper;
import java.math.*;
public class Pager {
? private int totalRows; //總行數(shù)
? private int pageSize = 10; //每頁顯示的行數(shù)
? private int currentPage; //當(dāng)前頁號(hào)
? private int totalPages; //總頁數(shù)
? private int startRow; //當(dāng)前頁在數(shù)據(jù)庫中的起始行
? public Pager() {
? }
? public Pager(int _totalRows) {
??? totalRows = _totalRows;
??? totalPages=totalRows/pageSize;
??? int mod=totalRows%pageSize;
??? if(mod>0){
????? totalPages++;
??? }
??? currentPage = 1;
??? startRow = 0;
? }
? public int getStartRow() {
??? return startRow;
? }
? public int getTotalPages() {
??? return totalPages;
? }
? public int getCurrentPage() {
??? return currentPage;
? }
? public int getPageSize() {
??? return pageSize;
? }
? public void setTotalRows(int totalRows) {
??? this.totalRows = totalRows;
? }
? public void setStartRow(int startRow) {
??? this.startRow = startRow;
? }
? public void setTotalPages(int totalPages) {
??? this.totalPages = totalPages;
? }
? public void setCurrentPage(int currentPage) {
??? this.currentPage = currentPage;
? }
? public void setPageSize(int pageSize) {
??? this.pageSize = pageSize;
? }
? public int getTotalRows() {
??? return totalRows;
? }
? public void first() {
??? currentPage = 1;
??? startRow = 0;
? }
? public void previous() {
??? if (currentPage == 1) {
????? return;
??? }
??? currentPage--;
??? startRow = (currentPage - 1) * pageSize;
? }
? public void next() {
??? if (currentPage < totalPages) {
????? currentPage++;
??? }
??? startRow = (currentPage - 1) * pageSize;
? }
? public void last() {
??? currentPage = totalPages;
??? startRow = (currentPage - 1) * pageSize;
? }
? public void refresh(int _currentPage) {
??? currentPage = _currentPage;
??? if (currentPage > totalPages) {
????? last();
??? }
? }
}
Pager類用于計(jì)算首頁、前一頁、下一頁、尾頁的在數(shù)據(jù)庫中的起始行，當(dāng)前的頁碼。
2.PagerHelp類
package com.jpcf.db.helper;
import javax.servlet.http.*;
public class PagerHelper {
? public static Pager getPager(HttpServletRequest httpServletRequest,int totalRows) {
??? //定義pager對(duì)象，用于傳到頁面
??? Pager pager = new Pager(totalRows);
??? //從Request對(duì)象中獲取當(dāng)前頁號(hào)
??? String currentPage = httpServletRequest.getParameter("currentPage");
??? //如果當(dāng)前頁號(hào)為空，表示為首次查詢?cè)擁?
??? //如果不為空，則刷新pager對(duì)象，輸入當(dāng)前頁號(hào)等信息
??? if (currentPage != null) {
????? pager.refresh(Integer.parseInt(currentPage));
??? }
??? //獲取當(dāng)前執(zhí)行的方法，首頁，前一頁，后一頁，尾頁。
??? String pagerMethod = httpServletRequest.getParameter("pageMethod");
??? if (pagerMethod != null) {
????? if (pagerMethod.equals("first")) {
??????? pager.first();
????? } else if (pagerMethod.equals("previous")) {
??????? pager.previous();
????? } else if (pagerMethod.equals("next")) {
??????? pager.next();
????? } else if (pagerMethod.equals("last")) {
??????? pager.last();
????? }
??? }
??? return pager;
? }
}
PageHelper這個(gè)類，我不用說應(yīng)該也知道用來干嘛了
3.DAO類
package com.jpcf.db.dao;
import com.jpcf.db.model.*;
import com.jpcf.db.helper.HibernateUtil;
import net.sf.hibernate.*;
import java.util.*;
import com.jpcf.db.controller.*;
public class VehiclePropertyDAO {
? public Collection findWithPage(int pageSize, int startRow) throws HibernateException {
??? Collection vehicleList = null;
??? Transaction tx = null;
??? try {
????? Session session = HibernateUtil.currentSession();
????? tx = session.beginTransaction();
????? Query q = session.createQuery("from VehicleProperty vp");
????? q.setFirstResult(startRow);
????? q.setMaxResults(pageSize);
????? vehicleList = q.list();
????? tx.commit();
??? } catch (HibernateException he) {
????? if (tx != null) {
??????? tx.rollback();
????? }
????? throw he;
??? } finally {
????? HibernateUtil.closeSession();
??? }
??? return vehicleList;
? }
? public int getRows(String query) throws HibernateException {
??? int totalRows = 0;
??? Transaction tx = null;
??? try {
????? Session session = HibernateUtil.currentSession();
????? tx = session.beginTransaction();
????? totalRows = ((Integer) session.iterate(query).next()).intValue();
????? tx.commit();
??? } catch (HibernateException he) {
????? if (tx != null) {
??????? tx.rollback();
????? }
????? throw he;
??? } finally {
????? HibernateUtil.closeSession();
??? }
??? return totalRows;
? }
}
DAO類我就貼這些分頁需要的代碼了。
“from VehicleProperty vp”也可以用一個(gè)參數(shù)傳進(jìn)來，有興趣的自己改一下吧
4.Action
下面是在Action中用到的代碼：
? public ActionForward execute(ActionMapping actionMapping,
???????????????????????????????????? ActionForm actionForm,
???????????????????????????????????? HttpServletRequest httpServletRequest,
???????????????????????????????????? HttpServletResponse httpServletresponse) {
???? Collection clInfos = null;//用于輸出到頁面的記錄集合
???? int totalRows;//記錄總行數(shù)
???? VehiclePropertyDAO vehicleDAO = new VehiclePropertyDAO();
??? //取得當(dāng)前表中的總行數(shù)
??? try {
????? totalRows = vehicleDAO.getRows("select count(*) from VehicleProperty");
??? } catch (Exception ex) {
????? servlet.log(ex.toString());
????? return actionMapping.findForward(Constants.FAILURE);
??? }
??? //通過PagerHelper類來獲取用于輸出到頁面的pager對(duì)象
??? Pager pager=PagerHelper.getPager(httpServletRequest,totalRows);
??? //取出從startRow開始的pageSize行記錄
??? try {
????? clInfos = vehicleDAO.findWithPage(pager.getPageSize(), pager.getStartRow());
??? } catch (Exception ex) {
????? servlet.log(ex.toString());
????? return actionMapping.findForward(Constants.FAILURE);
??? }
??? //把輸出的記錄集和pager對(duì)象保存到request對(duì)象中
??? httpServletRequest.setAttribute("CLINFOS", clInfos);
??? httpServletRequest.setAttribute("PAGER", pager);
??? return actionMapping.findForward(Constants.SUCCESS);
? }
?? 查詢語句select count(*) from VehicleProperty 也可以換成你需要的任意的條件（select count(*)?
from VehicleProperty where ..)
5.JSP頁面使用
下面就是在JSP中的應(yīng)用了：
<td colspan="8" align="right" class="head">
?? 第<bean:write name="PAGER" property="currentPage"/>頁?
?? 共<bean:write name="PAGER" property="totalPages"/>頁?
?? <html:link action="/bussiness/clInfo/queryWithPage.do?method=queryWithPage&pageMethod=first"?
paramName="PAGER" paramProperty="currentPage" paramId="currentPage">首頁</html:link>
?? <html:link action="/bussiness/clInfo/queryWithPage.do?method=queryWithPage&pageMethod=previous"?
paramName="PAGER" paramProperty="currentPage" paramId="currentPage">上一頁</html:link>
?? <html:link action="/bussiness/clInfo/queryWithPage.do?method=queryWithPage&pageMethod=next"?
paramName="PAGER" paramProperty="currentPage" paramId="currentPage">下一頁</html:link>
?? <html:link action="/bussiness/clInfo/queryWithPage.do?method=queryWithPage&pageMethod=last"?
paramName="PAGER" paramProperty="currentPage" paramId="currentPage">尾頁</html:link>
</td>
?? 解釋一下這一行:"/bussiness/clInfo/queryWithPage.do?method=queryWithPage&pageMethod=first
method=queryWithPage 是由于我的Action繼承的是DispatchAction,需要一個(gè)method參數(shù)
pageMethod=first 是用來在PageHelper類中判斷執(zhí)行哪個(gè)操作
四、總結(jié)
??? 我做的這個(gè)也只是一個(gè)借鑒，還有很多沒有實(shí)現(xiàn)的，比如還可以加一下 go 直接到第n頁的功能。
??? 其實(shí)最關(guān)鍵的是把當(dāng)前頁號(hào)和要執(zhí)行的是功能(上一頁，下一頁)的參數(shù)從頁面?zhèn)鬟M(jìn)來，在Action中就可以根據(jù)這兩個(gè)參數(shù)去取下一個(gè)頁面上要顯示的記錄集了。