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。
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持phpstudy。