大家好，欢迎来到雄雄的小课堂，昨天分享了关于分页查询的理论知识，今天我们就来结合代码和案例实际的应用一下，方便大家理解。
前言：我们都知道，实现分页需要三个步骤。第一，确定页大小（每页显示的数据量）。第二，计算显示的总页数。第三，写分页的sql语句。这三步已经在昨天的推文中详细说明，需要的可以点击这里快速浏览：javaweb中实现分页，持续更新……
01
开发环境
Myeclipse 10.5
Mysql 5.5
Tomcat 7.0
JDK 1.7
Chrome浏览器
02
数据库和表结构：
下面是表中的测试数据，需要说明的是saddress这一列，本来是当做地址的，现在有其他的需求，就当成了角色使用，但是并不影响分页。
03
Javaweb代码
Java代码是以分层开发的思想来实现的，其中有实体类：Student，Dao类和接口：BaseDaoNew,IStudentDao，Dao层实现类StudentDaoImpl：Service接口和实现类IStudentService，StudentService以及最后的工具类PageUtils
代码如下
实体类：Student
package org.entity;
/**
*
* @author 24519
* 学生的实体类
*
*/
public class Student {
private int sid;
private String sname;
private String sphone;
private String spass;
private String saddress;
private int sage;
//封装
public int getSid() {
return sid;
}
public void setSid(int sid) {
this.sid = sid;
}
public String getSname() {
return sname;
}
public void setSname(String sname) {
this.sname = sname;
}
public String getSphone() {
return sphone;
}
public void setSphone(String sphone) {
this.sphone = sphone;
}
public String getSpass() {
return spass;
}
public void setSpass(String spass) {
this.spass = spass;
}
public String getSaddress() {
return saddress;
}
public void setSaddress(String saddress) {
this.saddress = saddress;
}
public int getSage() {
return sage;
}
public void setSage(int sage) {
this.sage = sage;
}
}BaseDaoNew：
package org.dao;
import java.sql.*;
import java.util.List;
import com.sun.org.glassfish.external.statistics.annotations.Reset;
/**
*
* @author 24519
* 连接数据库的工作类
*
*/
public class BaseDaoNew {
private Connection conn = null;
private PreparedStatement pre;
private ResultSet rs;
//连接数据库
public Connection getConn(){
try{
//加载驱动
Class.forName("com.mysql.jdbc.Driver");
//数据库连接字符串
String url
= "jdbc:mysql://localhost:3306/schooldb?user=root&password=root";
//连接数据库
conn = DriverManager.getConnection(url);
}catch(Exception ex){
ex.printStackTrace();
}
return conn;
}
//增删改
public int ExecuteUpdate(String sql,List params) throws SQLException{
int rel = 0;
conn = getConn();
pre = conn.prepareStatement(sql);
if(params!=null){
for(int i = 0;i<params.size();i++){
pre.setObject(i+1, params.get(i));
}
}
rel = pre.executeUpdate();
return rel;
}
//查询
public ResultSet ExecuteQuerty(String sql,List params) throws SQLException{
conn = getConn();
pre = conn.prepareStatement(sql);
if(params!=null){
for(int i = 0;i<params.size();i++){
pre.setObject(i+1, params.get(i));
}
}
return pre.executeQuery();
}
//关闭连接
public void closeConn(Connection conn,
PreparedStatement pre,ResultSet rs){
try {
if(rs!=null){
rs.close();
}
if(pre!=null){
pre.close();
}
if(conn!=null){
conn.close();
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}IStudentDao：
package org.dao;
import java.util.List;
import org.entity.Student;
//学生信息的接口
public interface IStudentDao {
//增加学生信息
public int addStudent(Student stu);
//修改学生信息
public int updateStudent(Student stu);
//删除学生信息
public int delStudent(int sid);
//根据编号查询学生信息
public Student findStudentById(int sid);
//查询全部学生信息
public List<Student> findStudentAll();
//登录
public Student login(String name,String pass);
//总记录数
public int findAllStudentCount();
//分页查询
public List<Student> findStudentByPage(int currIndex,int pageSize);
}StudentDaoImpl：
package org.dao.impl;
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 org.dao.BaseDao;
import org.dao.BaseDaoNew;
import org.dao.IStudentDao;
import org.entity.Student;
import com.sun.xml.internal.ws.Closeable;
/**
*
* @author 24519
* 学生信息的实现类
*
*/
public class StudentDaoImpl implements IStudentDao {
BaseDao base = new BaseDao();
private Connection conn = base.getConn();
PreparedStatement pre = null;
ResultSet rs = null;
@Override
public int addStudent(Student stu) {
int rel = 0;
String sql = "insert into Student values(?,?,?,?,?,?);";
try {
List<Object> params = new ArrayList<Object>();
params.add(stu.getSid());
params.add(stu.getSname());
params.add(stu.getSphone());
params.add(stu.getSpass());
params.add(stu.getSaddress());
params.add(stu.getSage());
rel = base.ExecuteUpdate(sql, params);
} catch (SQLException e) {
e.printStackTrace();
}finally{
base.closeConn(conn, pre, rs);
}
return rel;
}
@Override
public int updateStudent(Student stu) {
String sql = "update student set sname = ?," +
"sphone = ?,spass=?,saddress=?,sage=? where sid = ?";
int rel = 0;
try {
List<Object> params = new ArrayList<Object>();
params.add(stu.getSname());
params.add(stu.getSphone());
params.add(stu.getSpass());
params.add(stu.getSaddress());
params.add(stu.getSage());
params.add(stu.getSid());
rel = base.ExecuteUpdate(sql, params);
} catch (SQLException e) {
e.printStackTrace();
}finally{
base.closeConn(conn, pre, rs);
}
return rel;
}
@Override
public int delStudent(int sid) {
String sql = "delete from Student where sid = ?";
int rel = 0;
try {
List<Object> params = new ArrayList<Object>();
params.add(sid);
rel = base.ExecuteUpdate(sql, params);
} catch (SQLException e) {
e.printStackTrace();
}finally{
base.closeConn(conn, pre, rs);
}
return rel;
}
@Override
public Student findStudentById(int sid) {
Student student = new Student();
String sql = "select * from student where sid = ?";
try {
List<Object> params = new ArrayList<Object>();
params.add(sid);
rs = base.ExecuteQuery(sql, params);
while(rs.next()){
student.setSid(rs.getInt(1));
student.setSname(rs.getString(2));
student.setSphone(rs.getString(3));
student.setSpass(rs.getString(4));
student.setSaddress(rs.getString("saddress"));
student.setSage(rs.getInt(6));
}
} catch (SQLException e) {
e.printStackTrace();
}finally{
base.closeConn(conn, pre, rs);
}
return student;
}
@Override
public List<Student> findStudentAll() {
List<Student> stus = new ArrayList<Student>();
String sql = "select * from Student";
try {
rs = base.ExecuteQuery(sql, null);
while(rs.next()){
Student student = new Student();
student.setSid(rs.getInt(1));
student.setSname(rs.getString(2));
student.setSphone(rs.getString(3));
student.setSpass(rs.getString(4));
student.setSaddress(rs.getString(5));
student.setSage(rs.getInt(6));
stus.add(student);//将信息放入集合中
}
} catch (SQLException e) {
e.printStackTrace();
}finally{
base.closeConn(conn, pre, rs);
}
return stus;
}
//登陆
@Override
public Student login(String name, String pass) {
Student student = new Student();
String sql = "select * from student where sname = ? and spass = ?;";
try {
List<Object> params = new ArrayList<Object>();
params.add(name);
params.add(pass);
rs = base.ExecuteQuery(sql, params);
while(rs.next()){
student.setSid(rs.getInt(1));
student.setSname(rs.getString(2));
student.setSphone(rs.getString(3));
student.setSpass(rs.getString(4));
student.setSaddress(rs.getString(5));
student.setSage(rs.getInt(6));
}
} catch (SQLException e) {
e.printStackTrace();
}
return student;
}
//查询总记录数
@Override
public int findAllStudentCount() {
String sql = "select count(*) from student";
int count = 0;
try {
rs = base.ExecuteQuery(sql, null);
rs.next();
count = rs.getInt(1);
} catch (SQLException e) {
e.printStackTrace();
}finally{
base.closeConn(conn, pre, rs);
}
return count;
}
//分页查询
@Override
public List<Student> findStudentByPage(int currIndex, int pageSize) {
String sql = "select * from student limit ? ,?";
int one = (currIndex-1)*pageSize;
List<Object> params = new ArrayList<Object>();
params.add(one);
params.add(pageSize);
List<Student> sList = new ArrayList<Student>();
try {
rs = base.ExecuteQuery(sql, params);
while(rs.next()){
Student stu = new Student();
stu.setSid(rs.getInt(1));
stu.setSname(rs.getString(2));
stu.setSphone(rs.getString(3));
stu.setSpass(rs.getString(4));
stu.setSaddress(rs.getString(5));
stu.setSage(rs.getInt(6));
sList.add(stu);
}
} catch (SQLException e) {
e.printStackTrace();
}finally{
base.closeConn(conn, pre, rs);
}
return sList;
}
}IStudentService：
package org.service;
import java.util.List;
import org.entity.Student;
public interface IStudentService {
//增加学生信息
public int addStudent(Student stu);
//修改学生信息
public int updateStudent(Student stu);
//删除学生信息
public int delStudent(int sid);
//根据编号查询学生信息
public Student findStudentById(int sid);
//查询全部学生信息
public List<Student> findStudentAll();
//登录
public Student login(String name,String pass);
//计算总记录数
public int findAllStudentCount();
//分页查询
public List<Student> findStudentByPage(int currIndex,int pageSize);
}StudentService：
package org.service.impl;
import java.util.List;
import org.dao.IStudentDao;
import org.dao.impl.StudentDaoImpl;
import org.entity.Student;
import org.service.IStudentService;
public class StudentServiceImpl implements IStudentService {
//创建Dao层的对象
private IStudentDao sDao = new StudentDaoImpl();
@Override
public int addStudent(Student stu) {
return sDao.addStudent(stu);
}
@Override
public int updateStudent(Student stu) {
return sDao.updateStudent(stu);
}
@Override
public int delStudent(int sid) {
return sDao.delStudent(sid);
}
@Override
public Student findStudentById(int sid) {
return sDao.findStudentById(sid);
}
@Override
public List<Student> findStudentAll() {
return sDao.findStudentAll();
}
@Override
public Student login(String name, String pass) {
return sDao.login(name, pass);
}
@Override
public int findAllStudentCount() {
return sDao.findAllStudentCount();
}
//分页查询
@Override
public List<Student> findStudentByPage(int currIndex, int pageSize) {
return sDao.findStudentByPage(currIndex, pageSize);
}
}PageUtils:
package org.utils;
import java.util.List;
import org.entity.Student;
/**
*
* @author 24519
* 分页的工具类
*
*/
public class PageUtils {
//页大小（每页显示多少条记录）
private int pageSize;
//当前页
private int currIndex;
//总记录数
private int totalCount;
//总页数
private int totalPage;
//每页显示的数据
List<Student> sList;
public int getPageSize() {
return pageSize;
}
public void setPageSize(int pageSize) {
this.pageSize = pageSize;
}
public int getCurrIndex() {
return currIndex;
}
//设置当前页
public void setCurrIndex(int currIndex) {
//判断当前页是否小于0，如果是，则默认第一页
if(currIndex<=0){
this.currIndex = 1;
}else{
this.currIndex = currIndex;
}
}
public int getTotalCount() {
return totalCount;
}
//计算总页数
public void setTotalCount(int totalCount) {
this.totalCount = totalCount;
int pages = totalCount%pageSize==0
?totalCount/pageSize
:totalCount/pageSize+1;
totalPage = pages;
}
public int getTotalPage() {
return totalPage;
}
public void setTotalPage(int totalPage) {
this.totalPage = totalPage;
}
public List<Student> getsList() {
return sList;
}
public void setsList(List<Student> sList) {
this.sList = sList;
}
}代码解析:我们可以看到，在IStudentDao中，除了有增删改和登录的接口外，还有两个接口，一个是查询总记录数，另一个为分页查询数据.
//总记录数
public int findAllStudentCount();
//分页查询
public List<Student> findStudentByPage(int currIndex,int pageSize);总记录数的作用就是对总页数进行计算，公式为，总页数=总记录数%页大小==0？总记录数/页大小:总记录数/页大小+1；
分页查询的数据，由于是多条，即返回List<Student>集合，每页显示5条数据，那我们就查询5条，即参数pageSize的值为5。currIndex的作用是用来记录当前页。
实现类对于这两个接口的关键代码如下：
//查询总记录数
@Override
public int findAllStudentCount() {
String sql = "select count(*) from student";
int count = 0;
try {
rs = base.ExecuteQuery(sql, null);
rs.next();
count = rs.getInt(1);
} catch (SQLException e) {
e.printStackTrace();
}finally{
base.closeConn(conn, pre, rs);
}
return count;
}
//分页查询
@Override
public List<Student> findStudentByPage(int currIndex, int pageSize) {
String sql = "select * from student limit ? ,?";
int one = (currIndex-1)*pageSize;
List<Object> params = new ArrayList<Object>();
params.add(one);
params.add(pageSize);
List<Student> sList = new ArrayList<Student>();
try {
rs = base.ExecuteQuery(sql, params);
while(rs.next()){
Student stu = new Student();
stu.setSid(rs.getInt(1));
stu.setSname(rs.getString(2));
stu.setSphone(rs.getString(3));
stu.setSpass(rs.getString(4));
stu.setSaddress(rs.getString(5));
stu.setSage(rs.getInt(6));
sList.add(stu);
}
} catch (SQLException e) {
e.printStackTrace();
}finally{
base.closeConn(conn, pre, rs);
}
return sList;
}PageUtils类的我们需要注意，在设置当前页currIndex的值时，要对齐进行判断，因为当前页永远永远的不可能小于0 或者大于总页数，设置的关键代码如下：
//设置当前页
public void setCurrIndex(int currIndex) {
//判断当前页是否小于0，如果是，则默认第一页
if(currIndex<=0){
this.currIndex = 1;
}else{
this.currIndex = currIndex;
}
}设置总记录数的关键代码如下：顺便对总页数进行计算
//计算总页数
public void setTotalCount(int totalCount) {
this.totalCount = totalCount;
int pages = totalCount%pageSize==0
?totalCount/pageSize
:totalCount/pageSize+1;
totalPage = pages;
}接下来就可以在表现层进行分页，我们在进分页查询的页面之前，先进doPage.jsp对数据进行处理，将所有需要用到的分页数据全部封装至PageUtils类中，完整实现代码如下：各个关键步骤均有注释
<%@page import="org.entity.Student"%>
<%@page import="org.service.impl.StudentServiceImpl"%>
<%@page import="org.service.IStudentService"%>
<%@page import="org.utils.PageUtils"%>
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
Student stu = (Student) request.getAttribute("student");
//判断是否是管理员
if (stu.getSaddress().equals("管理员")) {
//获取当前页，
//如果是空，默认是1
String curr = request.getParameter("currIndex");
if (curr == null) {
curr = "1";
}
Integer currIndex = Integer.parseInt(curr);
PageUtils p = new PageUtils();
p.setPageSize(5);
//计算总记录数
IStudentService s = new StudentServiceImpl();
//从数据库中查询总记录数
p.setTotalCount(s.findAllStudentCount());
//如果当前页大于等于总页数，那当前页就是总页数
if (currIndex >= p.getTotalPage()) {
currIndex = p.getTotalPage();
} else if (currIndex <= 0) {
//如果当前页小于等于0，则当前页等于1
currIndex = 1;
}
p.setCurrIndex(currIndex);
//从数据库中查询每页显示的数据放在集合中
List<Student> sList = s.findStudentByPage(currIndex, 5);
p.setsList(sList);
//将p对象放在request作用域中，在请求的页面中获取
request.setAttribute("p", p);
//跳转到分页的页面
request.getRequestDispatcher("findStudentPage.jsp").forward(
request, response);
} else {
//普通员工
//跳转到查询自己信息的页面
request.setAttribute("stu", stu);
request.getRequestDispatcher("shouInfo.jsp").forward(request,
response);
}
%>注意看这一行代码，当我们将一切处理完之后，通过这行代码转发至分页显示信息的页面，
request.getRequestDispatcher("findStudentPage.jsp").forward(request, response);
下面就是分页显示数据的页面了：
<%@page import="org.utils.PageUtils"%>
<%@page import="org.entity.Student"%>
<%@page import="org.service.impl.StudentServiceImpl"%>
<%@page import="org.service.IStudentService"%>
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP 'FindStudentPage.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
<%
//获取所有的数据
PageUtils p = (PageUtils)request.getAttribute("p");
//从工具类中获取每页显示的数据
List<Student> sList =p.getsList() ;
%>
<table border="1">
<tr>
<td>编号</td>
<td>姓名</td>
<td>电话</td>
<td>密码</td>
<td>地址</td>
<td>年龄</td>
</tr>
<%
for(Student stu :sList){
%>
<tr>
<td><%=stu.getSid() %></td>
<td><%=stu.getSname() %></td>
<td><%=stu.getSphone() %></td>
<td><%=stu.getSpass() %></td>
<td><%=stu.getSaddress()%></td>
<td><%=stu.getSage() %></td>
</tr>
<%
}
%>
</table>
<a href="doPage.jsp?currIndex=1">首页</a>
<a href="doPage.jsp?currIndex=<%=p.getCurrIndex()-1%>">上一页</a>
<%=p.getCurrIndex()%> / <%=p.getTotalPage()%>
<a href="doPage.jsp?currIndex=<%=p.getCurrIndex()+1%>">下一页</a>
<a href="doPage.jsp?currIndex=<%=p.getTotalPage()%>">末页</a>
<br/>
<form action="doPage.jsp" method="post">
至
<input type="number" max="<%=p.getTotalPage() %>" min="1" value="<%=p.getCurrIndex() %>" style="display:inline-block; 50px" name="currIndex"/>
页
<input type="submit" value="跳转">
</form>
</body>
</html>代码解析：
先从request中获取doPage.jsp中放入的数据，然后以表格的形式展示出来。
04
翻页解析
首页，很简单，当前页码必定是1，所以直接写currIndex=1即可。
上一页，假如当前也是2，那么上一页就是当前也减去1，所以上一页就是currIndex-1。
下一页，正好和上一页相反，即currIndex+1。
尾页，假如一共有5页，那么尾页就是5，即currIndex=5。
当前页和总页数由于我们在doPage都放在了PageUtils中，所以直接从PageUtils中获取即可。
注意我们无论是点击上一页还是下一页，或者首页尾页，均是跳转至doPage.jsp中操作，在doPage.jsp中，直接获取currIndex的值，然后在调用Service里面的方法进行分页查询。
运行结果如下：
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