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一个高效简洁的Struts分页方法(原创)

作者：未知 来源：月光软件站 加入时间：2005-2-28　月光软件站

    在网上看了几个Structs分页，感觉不是很完善，于是根据自己的经验，写了一个相对高效简洁的分页方法。由于本人水平有限，如果大家有什么更好的想法，欢迎不吝赐教。

一、 开发环境
我的开发环境是：JBuilder x + Weblogic 8.1 + Oracle 9i + Windows 2003 ，如果朋友们的开发环境不一样亦无妨。

二、开发思路
既然讲的是Struts，那自然离不了MVC，分页显示也是如此。
1、 建立数据库和对应的表，本例的表是TCertificate。
2、 建立适当的模型组件，对应你要查询数据库中的表。这部分由DAO数据访问层来实现，如果有的朋友对DAO不熟悉可以查询一下相关资料。本例由CertificateDAO.java来实现。
3 、建立分页所需要的模型组件，由javaBean来充当，并与CertificateDAO实现分离。网上介绍的很多方法，都存在着数据与分页组件藕合的现象，这也是本方法与其它分页方法的主要不同之处。

4、建立控制器组件，这部分由Struts 中的Action来实现。主要负责将实例化CertificateDAO，只取要显示的数据记录，存入ArrayList对象然后返回，并放到request中。而分页部分则根据分页条件，单独进行构造，避免了与DAO混在一起的情况发生。网上其它介绍的一些分页方法中，基本上都是一次性读出所有查询的数据，然后再由分页相关组件进行构造。这样，如果数据量大的话，很容易形成瓶颈。在本例中由于不是一次性地读出查询的所有数据，而只是读出一个页面要显示的数据记录，这就节省了很多不必要的数据传输，提高了效率。本例中为CertificateAction.java。

5、建立视图组件，这部分由jsp来充当，为了不出现java 代码，我们使用Struts提供的标签库，主要负责从request中取出刚刚放入的对象，通过反复调用CertificateAction以及action参数，而实现分页显示。本例中为listcertificate.jsp。
6、 建立并配置struts-config.xml。

三、实例代码
确定好上面的开发思路后，代码的实现就有单可循了。
1、建数据库和相应的表。
2、数据逻辑层的相关代码。
1）、通用的DAO类：CommonDAO.java
这是一个很多DAO都要继承到的通用DAO类，是我根据实践总结出来的，为了减少篇幅，这里只显示和本例相关的代码。


java代码:

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;
/**
  * 说明:取得当前查询的总记录数
  */
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;
    }
  }
}


这个类主要是通过子类传进来的先进结果集，取得查询的记录总数，并对数据库连接进行简单的管理。
2）、对数据库进行访问：CertificateDAO.java


java代码:

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();
                        /*对游标进行处理，rsHandler 方法在父类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)是查得所有要显示的数据，并放入ArrayList中。看过网上有些例子，把数据记录放入ArrayList的动作过程直接在while循环体里完成，如果字段多的话，会造成方法过于宠大，又不美观。 这里，数据记录放入ArrayList的动作过程由rs2VO方法完成，就比较整洁了。另外，if (rs != null && rs.next ()) 配合while ( (countRows++ < limit) && rs.next ()) 是为了程序的健壮性考虑的，稍分析一下不难得出结论。

3、建立控制器组件：CertificateAction.java


java代码:

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 ; //每页显示5条记录
        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;   //翻页时的起始记录所在游标
                        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(); //  取得总记录数
                        String url = request.getContextPath()+"/"+mapping.getPath()+".do";
                        String pagerHeader = Pager.generate(offset, size, length, url); //分页处理

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


CertificateAction.java主要是把数据从DAO中取出，并放入一个ArrayList 中，然后通过配置文件再软件View的JSP页。

5、建立视图listcertificate.jsp文件。

java代码:

<%@ 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、对应的配置文件struts-config.xml。

java代码:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE struts-config PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 1.1//EN" "http://jakarta.apache.org/struts/dtds/struts-config_1_1.dtd">
<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、最后当然是最重要的分页代码了：Pager.java

java代码:

package com.xindeco.common;

import java.util.* ;
public class Pager {
  private static int MAX_PAGE_INDEX = 10; //页脚显示多少页
  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 "";
        }
  }
}

这部分代码的实现相当简洁，但已经足够完成所需了。

 

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