紧接着上篇―分页技术原理与实现之分页的意义及方法（一） ，本篇继续分析分页技术。上篇讲的是分页技术的简单原理与介绍，这篇深入分析一下分页技术的代码实现。
上篇最后讲到了分页的最佳实现是在数据库层进行分页，而且不同的数据库有不同的分页实现，比如Oracle是用三层sql嵌套实现分页的、MySQL是用limit关键字实现的(上篇已讲到)。
这篇以Java+Oracle为基础，讲解代码层的实现。
就如平时我们很在分页中看到的，分页的时候返回的不仅包括查询的结果集(List)，而且还包括总的页数(pageNum)、当前第几页(pageNo)等等信息，所以我们封装一个查询结果PageModel类，代码如下：
package kane;import java.util.List;public class PageModel<E> { private List<E> list; private int pageNo; private int pageSize; private int totalNum; private int totalPage; public List<E> getList() { return list; } public void setList(List<E> list) { this.list = list; } public int getPageNo() { return pageNo; } public void setPageNo(int pageNo) { this.pageNo = pageNo; } public int getPageSize() { return pageSize; } public void setPageSize(int pageSize) { this.pageSize = pageSize; } public int getTotalNum() { return totalNum; } public void setTotalNum(int totalNum) { this.totalNum = totalNum; setTotalPage((getTotalNum() % pageSize) == 0 ? (getTotalNum() / pageSize) : (getTotalNum() / pageSize + 1)); } public int getTotalPage() { return totalPage; } public void setTotalPage(int totalPage) { this.totalPage = totalPage; } // 获取第一页 public int getFirstPage() { return 1; } // 获取最后页 public int getLastPage() { return totalPage; } // 获取前页 public int getPrePage() { if (pageNo > 1) return pageNo - 1; return 1; } // 获取后页 public int getBackPage() { if (pageNo < totalPage) return pageNo + 1; return totalPage; } // 判断'首页'及‘前页'是否可用 public String isPreable() { if (pageNo == 1) return "disabled"; return ""; } // 判断'尾页'及‘下页'是否可用 public String isBackable() { if (pageNo == totalPage) return "disabled"; return ""; }}其中使用泛型是为了能使的该分页类能进行重用，比如在查询用户时可以封装User对象、在查询财务中的流向单时可以封装流向单FlowCard类。
我们以查询用户为例，用户选择查询条件，首先调用Servlet获取查询参数，然后请求业务逻辑层取得分页封装结果类。业务逻辑调用Dao层取得结果集、取得中记录数封装成分页类。最后Servlet将结果设置到jsp页面显示。
首先来讲解Servlet，代码如下：
package kane;import java.io.*;import java.util.*;import javax.servlet.ServletConfig;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import kane.UserInfo;import kane.UserInfoManage;import kane.PageModel;public class UserBasicSearchServlet extends HttpServlet { private static final long serialVersionUID = 1L; private int pageSize = 0; @Override public void init(ServletConfig config) throws ServletException { pageSize = Integer.parseInt(config.getInitParameter("pageSize")); } @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doPost(req, resp); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { // 1.取得页面参数并构造参数对象 int pageNo = Integer.parseInt(req.getParameter("pageNo")); String sex = req.getParameter("gender"); String home = req.getParameter("newlocation"); String colleage = req.getParameter("colleage"); String comingyear = req.getParameter("ComingYear"); UserInfo u = new UserInfo(); u.setSex(sex); u.setHome(home); u.setColleage(colleage); u.setCy(comingyear); // 2.调用业务逻辑取得结果集 UserInfoManage userInfoManage = new UserInfoManage(); PageModel<UserInfo> pagination = userInfoManage.userBasicSearch(u, pageNo, pageSize); List<UserInfo> userList = pagination.getList(); // 3.封装返回结果 StringBuffer resultXML = new StringBuffer(); try { resultXML.append("<?xml version='1.0' encoding='gb18030'?>/n"); resultXML.append("<root>/n"); for (Iterator<UserInfo> iterator = userList.iterator(); iterator .hasNext();) { UserInfo userInfo = iterator.next(); resultXML.append("<data>/n"); resultXML.append("/t<id>" + userInfo.getId() + "</id>/n"); resultXML.append("/t<truename>" + userInfo.getTruename() + "</ truename >/n"); resultXML.append("/t<sex>" + userInfo.getSex() + "</sex>/n"); resultXML.append("/t<home>" + userInfo.getHome() + "</home>/n"); resultXML.append("</data>/n"); } resultXML.append("<pagination>/n"); resultXML.append("/t<total>" + pagination.getTotalPage() + "</total>/n"); resultXML.append("/t<start>" + pagination.getFirstPage() + "</start>/n"); resultXML.append("/t<end>" + pagination.getLastPage() + "</end>/n"); resultXML.append("/t<pageno>" + pagination.getPageNo() + "</pageno>/n"); resultXML.append("</pagination>/n"); resultXML.append("</root>/n"); } catch (Exception e) { e.printStackTrace(); } writeResponse(req, resp, resultXML.toString()); } public void writeResponse(HttpServletRequest request, HttpServletResponse response, String result) throws IOException { response.setContentType("text/xml"); response.setHeader("Cache-Control", "no-cache"); response.setHeader("Content-Type", "text/xml; charset=gb18030"); PrintWriter pw = response.getWriter(); pw.write(result); pw.close(); }}其中User对象代码如下：
package kane;import java.util.Date;public class UserInfo { private int id; private String username; private String password; private String truename; private String sex; private Date birthday; private String home; private String colleage; private String comingYear; public int getId() { return id; } public void setId(int id) { this.id = id; } public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } public String getPassword() { return password; } public void setPassword(String password) { this.password = password; } public String getTruename() { return truename; } public void setTruename(String truename) { this.truename = truename; } public String getSex() { return sex; } public void setSex(String sex) { this.sex = sex; } public Date getBirthday() { return birthday; } public void setBirthday(Date birthday) { this.birthday = birthday; } public String getHome() { return home; } public void setHome(String home) { this.home = home; } public String getColleage() { return colleage; } public void setColleage(String colleage) { this.colleage = colleage; } public String getCy() { return comingYear; } public void setCy(String cy) { this. comingYear= cy; }}接着是业务逻辑层代码，代码如下：
package kane;import java.sql.Connection;import kane.DBUtility;import kane.PageModel;public class UserInfoManage { private UserInfoDao userInfoDao = null; public UserInfoManage () { userInfoDao = new UserInfoDao(); } public PageModel<UserInfo> userBasicSearch(UserInfo u, int pageNo, int pageSize) throws Exception { Connection connection = null; PageModel<UserInfo> pagination = new PageModel<UserInfo>(); try { connection = DBUtility.getConnection(); DBUtility.setAutoCommit(connection, false); pagination.setList(userInfoDao.getUserList(u, pageNo, pageSize)); pagination.setPageNo(pageNo); pagination.setPageSize(pageSize); pagination.setTotalNum(userInfoDao.getTotalNum(u)); DBUtility.commit(connection); } catch (Exception e) { DBUtility.rollBack(connection); e.printStackTrace(); throw new Exception(); } finally { DBUtility.closeConnection(); } return pagination; }}其中DBUtility为数据库的连接封装类。
最后是Dao层代码实现，代码如下：
package kane;import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;import java.util.ArrayList;import java.util.List;import kane.UserInfo;import kane.DBUtility;public class UserInfoDao { public List<UserInfo> getUserList(UserInfo userInfo, int pageNo, int pageSize) throws Exception { PreparedStatement pstmt = null; ResultSet rs = null; List<UserInfo> userList = null; try { String sql = "select * from(select rownum num,u.* from(select * from user_info where sex = ? and home like '" + userInfo.getHome() + "%" + "' and colleage like '" + userInfo.getColleage() + "%" + "' and comingyear like '" + userInfo.getCy() + "%" + "' order by id) u where rownum<=?) where num>=?"; userList = new ArrayList<UserInfo>(); Connection conn = DBUtility.getConnection(); pstmt = conn.prepareStatement(sql); pstmt.setString(1, userInfo.getSex()); pstmt.setInt(2, pageNo * pageSize); pstmt.setInt(3, (pageNo - 1) * pageSize + 1); rs = pstmt.executeQuery(); while (rs.next()) { UserInfo user = new UserInfo(); user.setId(rs.getInt("id")); user.setTruename(rs.getString("truename")); user.setSex(rs.getString("sex")); user.setHome(rs.getString("home")); userList.add(user); } } catch (SQLException e) { e.printStackTrace(); throw new Exception(e); } finally { DBUtility.closeResultSet(rs); DBUtility.closePreparedStatement(pstmt); } return userList; } public int getTotalNum(UserInfo userInfo) throws Exception { PreparedStatement pstmt = null; ResultSet rs = null; int count = 0; try { String sql = "select count(*) from user_info where sex=? and home like '" + userInfo.getHome() + "%" + "' and colleage like '" + userInfo.getColleage() + "%" + "' and comingyear like '" + userInfo.getCy()+ "%" + "'"; Connection conn = DBUtility.getConnection(); pstmt = conn.prepareStatement(sql); pstmt.setString(1, userInfo.getSex()); rs = pstmt.executeQuery(); if (rs.next()) { count = rs.getInt(1); } } catch (SQLException e) { e.printStackTrace(); throw new Exception(e); } finally { DBUtility.closeResultSet(rs); DBUtility.closePreparedStatement(pstmt); } return count; }}最后就是servlet将得到的结果返回给jsp页面显示出来。
注：其中DBUtility代码是封装数据库连接操作的代码，如下：
package kane;import java.sql.Connection;import java.sql.DriverManager;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;public class DBUtility { private static ThreadLocal<Connection> threadLocal = new ThreadLocal<Connection>(); public static Connection getConnection() { Connection conn = null; conn = threadLocal.get(); if (conn == null) { try { Class.forName("oracle.jdbc.driver.OracleDriver"); conn = DriverManager.getConnection( "jdbc:oracle:thin:@localhost:1521:oracle", "admin", "admin"); threadLocal.set(conn); } catch (ClassNotFoundException e) { e.printStackTrace(); } catch (SQLException e) { e.printStackTrace(); } } return conn; } // 封装设置Connection自动提交 public static void setAutoCommit(Connection conn, Boolean flag) { try { conn.setAutoCommit(flag); } catch (SQLException e) { e.printStackTrace(); } } // 设置事务提交 public static void commit(Connection conn) { try { conn.commit(); } catch (SQLException e) { e.printStackTrace(); } } // 封装设置Connection回滚 public static void rollBack(Connection conn) { try { conn.rollback(); } catch (SQLException e) { e.printStackTrace(); } } // 封装关闭Connection、PreparedStatement、ResultSet的函数 public static void closeConnection() { Connection conn = threadLocal.get(); try { if (conn != null) { conn.close(); conn = null; threadLocal.remove(); } } catch (SQLException e) { e.printStackTrace(); } } public static void closePreparedStatement(PreparedStatement pstmt) { try { if (pstmt != null) { pstmt.close(); pstmt = null; } } catch (SQLException e) { e.printStackTrace(); } } public static void closeResultSet(ResultSet rs) { try { if (rs != null) { rs.close(); rs = null; } } catch (SQLException e) { e.printStackTrace(); } }}使用ThreadLocal是为了保证事务的一致，使得同一个线程的所有数据库操作使用同一个Connection。
到此一个简单的代码实现就完成了。
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