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在網(wǎng)上看了幾個(gè)Structs分頁(yè)，感覺(jué)不是很完善，于是根據自己的經(jīng)驗，寫(xiě)了一個(gè)相對高效簡(jiǎn)潔的分頁(yè)方法。由于本人水平有限，如果大家有什么更好的想法，歡迎不吝賜教。

一、 開(kāi)發(fā)環(huán)境
我的開(kāi)發(fā)環(huán)境是：JBuilder x + Weblogic 8.1 + Oracle 9i + Windows 2003 ，如果朋友們的開(kāi)發(fā)環(huán)境不一樣亦無(wú)妨。

二、開(kāi)發(fā)思路
既然講的是Struts，那自然離不了MVC，分頁(yè)顯示也是如此。
1、 建立數據庫和對應的表，本例的表是TCertificate。
2、 建立適當的模型組件，對應你要查詢(xún)數據庫中的表。這部分由DAO數據訪(fǎng)問(wèn)層來(lái)實(shí)現，如果有的朋友對DAO不熟悉可以查詢(xún)一下相關(guān)資料。本例由CertificateDAO.java來(lái)實(shí)現。
3 、建立分頁(yè)所需要的模型組件，由javaBean來(lái)充當，并與CertificateDAO實(shí)現分離。網(wǎng)上介紹的很多方法，都存在著(zhù)數據與分頁(yè)組件藕合的現象，這也是本方法與其它分頁(yè)方法的主要不同之處。

4、建立控制器組件，這部分由Struts 中的Action來(lái)實(shí)現。主要負責將實(shí)例化CertificateDAO，只取要顯示的數據記錄，存入ArrayList對象然后返回，并放到request中。而分頁(yè)部分則根據分頁(yè)條件，單獨進(jìn)行構造，避免了與DAO混在一起的情況發(fā)生。網(wǎng)上其它介紹的一些分頁(yè)方法中，基本上都是一次性讀出所有查詢(xún)的數據，然后再由分頁(yè)相關(guān)組件進(jìn)行構造。這樣，如果數據量大的話(huà)，很容易形成瓶頸。在本例中由于不是一次性地讀出查詢(xún)的所有數據，而只是讀出一個(gè)頁(yè)面要顯示的數據記錄，這就節省了很多不必要的數據傳輸，提高了效率。本例中為CertificateAction.java。

5、建立視圖組件，這部分由jsp來(lái)充當，為了不出現java 代碼，我們使用Struts提供的標簽庫，主要負責從request中取出剛剛放入的對象，通過(guò)反復調用CertificateAction以及action參數，而實(shí)現分頁(yè)顯示。本例中為listcertificate.jsp。
6、 建立并配置struts-config.xml。

三、實(shí)例代碼
確定好上面的開(kāi)發(fā)思路后，代碼的實(shí)現就有單可循了。
1、建數據庫和相應的表。
2、數據邏輯層的相關(guān)代碼。
1）、通用的DAO類(lèi)：CommonDAO.java
這是一個(gè)很多DAO都要繼承到的通用DAO類(lèi)，是我根據實(shí)踐總結出來(lái)的，為了減少篇幅，這里只顯示和本例相關(guān)的代碼。

java代碼: 

package com.xindeco.business ;
import java.io.*;
import java.sql.*;
import java.util.*;
import javax.sql.*;
import java.lang.IllegalAccessException;
import java.lang.reflect.InvocationTargetException;
import org.apache.commons.beanutils.BeanUtils;
public class DAO
{
  protected DataSource ds;
/**
  * 說(shuō)明:取得當前查詢(xún)的總記錄數
  */
public int getRows ()
{
  return this.count;
}
  public void rsHandler (ResultSet rs, int offset, int limit)
  {
   try
   {
    count = 0;
    rs.absolute ( -1) ;
    count = rs.getRow () ;
    if (offset <= 0)
    {
     rs.beforeFirst () ;
    }
    else
    {
     rs.absolute (offset) ;
    }
   }
   catch (Exception e)
   {
    e.printStackTrace () ;
   }
  }
  public DAO(DataSource ds) {
          this.ds = ds;
  }

  public void setDataSource(DataSource ds) {
    this.ds = ds;
  }

  protected void close(ResultSet rs) {
    if (rs != null) {
            try {
                    rs.close();
            } catch (SQLException e) {
            }
            rs = null;
    }
  }

  protected void close(PreparedStatement pstmt) {
    if (pstmt != null) {
            try {
                    pstmt.close();
            } catch (SQLException e) {
            }
            pstmt = null;
    }
  }
  protected void close(Connection conn) {
    if (conn != null) {
            try {
                    conn.close();
            } catch (SQLException e) {
                    e.printStackTrace();
            }
            conn = null;
    }
  }

  protected void rollback(Connection conn) {
    if (conn != null) {
            try {
                    conn.rollback();
            } catch (SQLException e) {
                    e.printStackTrace();
            }
            conn = null;
    }
  }
}

這個(gè)類(lèi)主要是通過(guò)子類(lèi)傳進(jìn)來(lái)的先進(jìn)結果集，取得查詢(xún)的記錄總數，并對數據庫連接進(jìn)行簡(jiǎn)單的管理。
2）、對數據庫進(jìn)行訪(fǎng)問(wèn)：CertificateDAO.java

java代碼: 

package com.xindeco.business;

import java.io.*;
import java.sql.*;
import java.util.*;
import javax.sql.*;

import com.xindeco.common.dbconn.DbConn;

public class CertificateDAO extends DAO
{

  public NationDAO(DataSource ds) {
    super(ds);
  }

public List findCertificateList(int offset,int limit) throws SQLException
        {
        int countRows = 0 ;
        ArrayList list = null ;
    Connection conn = null;
    PreparedStatement pstmt = null;
ResultSet rs = null;
try
        {
             conn = ds.getConnection();
                String sql =
                                "SELECT certificateID, certificateCode,certificateName,photoURL,"
                                + "description,graduateID FROM TCertificate " ;
      pstmt = conn.prepareStatement(sql);
      rs = pstmt.executeQuery();
                        /*對游標進(jìn)行處理，rsHandler 方法在父類(lèi)DAO中*/
                        this.rsHandler(rs,offset,limit);
                        if (rs != null && rs.next ())
                        {
                                list = new ArrayList () ;
                                do
                                {
                                        countRows++ ;
                                        list.add (rs2VO (rs)) ;
                                }
                                while ( (countRows++ < limit) && rs.next ()) ;
                        }
      close(rs);
      close(pstmt);
          } catch (SQLException e) {
      close(rs);
      close(pstmt);
      rollback(conn);
                e.printStackTrace();
                  }
finally {
            close(conn);
    }
        return list ;
        }

        private CertificateVO rs2VO (ResultSet rs)
        {
                try
                {
                        CertificateVO certificateVO = new CertificateVO () ;
                        certificateVO.setCertificateID (rs.getInt ("certificateID")) ;
                        certificateVO.setCertificateCode (rs.getString ("certificateCode")) ;
                        certificateVO.setCertificateName (rs.getString ("certificateName")) ;
                        certificateVO.setPhotoURL (rs.getString ("photoURL")) ;
                        certificateVO.setDescription (rs.getString ("description")) ;
                        certificateVO.setGraduateID (rs.getInt ("graduateID")) ;
                        return certificateVO ;
                }
                catch (Exception ex)
                {
                        ex.printStackTrace () ;
                        return null ;
                }
        }
}

findCertificateList(int offset,int limit)是查得所有要顯示的數據，并放入ArrayList中?？催^(guò)網(wǎng)上有些例子，把數據記錄放入ArrayList的動(dòng)作過(guò)程直接在while循環(huán)體里完成，如果字段多的話(huà)，會(huì )造成方法過(guò)于寵大，又不美觀(guān)。 這里，數據記錄放入ArrayList的動(dòng)作過(guò)程由rs2VO方法完成，就比較整潔了。另外，if (rs != null && rs.next ()) 配合while ( (countRows++ < limit) && rs.next ()) 是為了程序的健壯性考慮的，稍分析一下不難得出結論。

3、建立控制器組件：CertificateAction.java

java代碼: 

package com.xindeco.presentation;

import javax.sql.* ;
import java.util.* ;

import javax.servlet.http.* ;
import javax.servlet.* ;

import org.apache.struts.action.* ;
import org.apache.struts.util.* ;

import com.xindeco.common.Pager;
import com.xindeco.business.graduatedata.CertificateDAO ;

public class CertificateAction
        extends Action
{
        private static final int PAGE_LENGTH = 5 ; //每頁(yè)顯示5條記錄
        public ActionForward execute (ActionMapping mapping, ActionForm form,
                                                                  HttpServletRequest request,
                                                                  HttpServletResponse response)
        {
                ActionForward myforward = null ;
                String myaction = mapping.getParameter () ;

                if (isCancelled (request))
                {
                        return mapping.findForward ("failure") ;
                }
                if ("".equalsIgnoreCase (myaction))
                {
                        myforward = mapping.findForward ("failure") ;
                }
                else if        ("LIST".equalsIgnoreCase (myaction))
                {
                        myforward = performList (mapping, form, request, response) ;
                }
                else
                {
                        myforward = mapping.findForward ("failure") ;
                }
                return myforward ;
        }

        private ActionForward performList (ActionMapping mapping,
                                                                           ActionForm actionForm,
                                                                           HttpServletRequest request,
                                                                           HttpServletResponse response)
        {
                     try
                {
        DataSource ds = (DataSource) servlet.getServletContext().getAttribute(Action.DATA_SOURCE_KEY);

                CertificateDAO   certificateDAO  = new CertificateDAO  (ds) ;

                        int offset = 0;   //翻頁(yè)時(shí)的起始記錄所在游標
                        int length = PAGE_LENGTH; 
                        String pageOffset = request.getParameter("pager.offset");
                if (pageOffset == null || pageOffset.equals("")) {
        offset = 0;
      } else {
        offset = Integer.parseInt(pageOffset);
      }
                        List certificateList = certificateDAO .findCertificateList (offset,length) ;
                        int size = certificateDAO.getRows(); //  取得總記錄數
                        String url = request.getContextPath()+"/"+mapping.getPath()+".do";
                        String pagerHeader = Pager.generate(offset, size, length, url); //分頁(yè)處理

                        request.setAttribute ("pager", pagerHeader) ;
                        request.setAttribute ("list", certificateList) ;
                }
                catch (Exception e)
                {
                        e.printStackTrace();
                        return mapping.findForward ("error") ;
                }
                return mapping.findForward ("success") ;
        }
}

CertificateAction.java主要是把數據從DAO中取出，并放入一個(gè)ArrayList 中，然后通過(guò)配置文件再軟件View的JSP頁(yè)。

5、建立視圖listcertificate.jsp文件。

java代碼: 

<%@ page contentType="text/html; charset=GBK" %>
<%@ taglib uri="/WEB-INF/struts-template.tld" prefix="template" %>
<%@ taglib uri="/WEB-INF/struts-html.tld" prefix="html" %>
<%@ taglib uri="/WEB-INF/struts-bean.tld" prefix="bean" %>
<%@ taglib uri="/WEB-INF/struts-logic.tld" prefix="logic" %>

<table bgcolor="#666666" cellpadding="1" cellspacing="0" border="0" width="500">
<tr>
<td>
<table cellpadding="0" cellspacing="0" border="0" width="500">
<tr>
<td bgcolor="#fecc51">&</td>
</tr>
</table>
</td>
</tr>
<tr>
<td>
<table cellpadding="0" cellspacing="0" border="0" width="500">
  <tr>
<td bgcolor="#d6e0ed">
    &&<bean:message key="label.list4certificate"/>
  </td>
</tr>
<tr bgcolor="#FFFFFF">
<td width="5%"></td><td width="19%"></td><td width="76%"></td>
</tr>
    <tr>
<td>
<table bgcolor="#f2f2f2" width="500" cellspacing="0" border="0">
      <tr bgcolor="#bacce1">
        <td><b><bean:message key="Certificate.select"/> </b></td>
        <td><b><bean:message key="Certificate.certificateID"/> </b></td>
        <td><b><bean:message key="Certificate.certificateCode"/></b></td>
        <td><b><bean:message key="Certificate.certificateName"/></b></td>
        <td><b><bean:message key="Certificate.view"/></b></td>
    /tr>

<bean:write name="pager" property="description"/>
  <logic:equal name="pager" property="hasPrevious" value="true">
              <a href="/graduatedata/list.do?viewPage=<bean:write name="pager" property="previousPage"/>" class="a02">
           Previous
        </a>
  </logic:equal>
  <logic:equal name="pager" property="hasNext" value="true">
    a href="/graduatedata/list.do?viewPage=<bean:write name="pager" property="nextPage"/>" class="a02">
     Next
    /a>
  </logic:equal>

<logic:notEmpty name="list" scope="request">
<logic:iterate id="certificate" name="list" type="com.xindeco.business.graduatedata.CertificateVO"scope="request">
<tr bgcolor="#FFFFFF">
    td><html:text property="name" value="<bean:write name="certificate" property="certificateID" scope="page"/>"/>
                </td>
    td> <bean:write name="certificate" property="certificateID" scope="page"/></td>
    td> <bean:write name="certificate" property="certificateCode" scope="page"/></td>
    td> <bean:write name="certificate" property="certificateName" scope="page"/></td>
    td> <bean:write name="certificate" property="photoURL" scope="page"/></td>
</tr>
</logic:iterate>
</logic:notEmpty>
</table>
</td>
</tr>
</table>
</td>
</tr>
</table>

6、對應的配置文件struts-config.xml。

java代碼: 

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE struts-config PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 1.1//EN" "<struts-config>
  <form-beans>
    <form-bean name="certificateForm" type="com.xindeco.presentation.graduatedata.CertificateForm" />
  </form-beans>
  <global-forwards>
    <forward name="error" path="/error/error.jsp" />
  </global-forwards>
  <action-mappings>
      <action name="certificateForm" parameter="LIST" path="/graduatedata/list" scope="request" type="com.xindeco.presentation.graduatedata.CertificateAction" validate="true">
      <forward name="success" path="/graduatedata/listcertificate.jsp" />
    </action>
  </action-mappings>
……
</struts-config>

7、最后當然是最重要的分頁(yè)代碼了：Pager.java

java代碼: 

package com.xindeco.common;

import java.util.* ;
public class Pager {
  private static int MAX_PAGE_INDEX = 10; //頁(yè)腳顯示多少頁(yè)
  private static String HEADER = "Result page";
 
  public static String generate(int offset, int length, int size, String url) {
        if (length > size) {
          String pref;
          if (url.indexOf("?") > -1) {
                pref = "&";
          } else {
                pref = "?";
          }
          String header = "<font face=‘Helvetica‘ size=‘-1‘>"+HEADER+": ";
          if (offset > 0) {
                header += "&<a href=\""+url+pref+"pager.offset="+(offset-size)+"\">[<< Prev]</a>\n";
          }
          int start;
          int radius = MAX_PAGE_INDEX/2*size;
          if (offset < radius) {
                start = 0;
          } else if(offset < length-radius) {
                start = offset - radius;
          } else {
                start = (length/size-MAX_PAGE_INDEX)*size;
          }
          for(int i=start;i<length && i < start + MAX_PAGE_INDEX*size;i+=size) {
                if (i == offset) {
                  header += "<b>"+(i/size+1)+"</b>\n";
                } else {
                  header += "&<a href=\""+url+pref+"pager.offset="+i+"\">"+(i/size+1)+"</a>\n";
                }
          }
          if(offset < length - size) {
                header += "&<a href=\""+url+pref+"pager.offset="+((int)offset+(int)size)+"\">[Next >>]</a>\n";
          }
          header += "</font>";
          return header;
        } else {
          return "";
        }
  }
}

這部分代碼的實(shí)現相當簡(jiǎn)潔，但已經(jīng)足夠完成所需了。