在设计信息浏览页面时,如果信息量很大,则经常需要分页显示信息。在这种情况下,分页技术就可以很好的帮助到我们。
目录
1.分页技术的设计思想
按照“表示层--控制层--DAO层--数据层”的分层设计思想:首先DAO对象提供分页查询的方法;在控制层调用DAO中的方法完成指定页数据的查询;然后在表示层通过EL表达式和JSTL将该页数据显示出来。
2.分页的具体实现
①在DAO对象中提供两个方法用来计算总页数和查询指定页数据。
②控制层提供一个servlet类,调用DAO对象查询数据并指派页面显示数据。
③输出页面使用EL和JSTL显示查询结果
3.分页实例
User.java--暂时记录信息
package bean2;
public class User {
private String id;
private String name;
private String sex;
public User() {
super();
// TODO Auto-generated constructor stub
}
public User(String id, String name, String sex) {
super();
this.id = id;
this.name = name;
this.sex = sex;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
}
JdbcUtil.java--连接数据库
package bean2;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;
public class JdbcUtil {
private static String driver;
private static String url;
private static String user;
private static String password;
private static Properties pr=new Properties();
public JdbcUtil(){
super();
}
static
{
try {
pr.load(JdbcUtil.class.getClassLoader().getResourceAsStream("db.properties"));
driver=pr.getProperty("driver");
url=pr.getProperty("url");
user=pr.getProperty("user");
password=pr.getProperty("password");
try {
Class.forName(driver);
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public static Connection getConnection() throws SQLException
{
return DriverManager.getConnection(url,user,password);
}
public static void free(Connection conn,Statement pstmt,ResultSet rs) throws Exception
{
if(conn!=null){conn.close();}
if(pstmt!=null){pstmt.close();}
if(rs!=null){rs.close();}
}
}
db.properties--记录数据库信息
driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/ccc?useUnicode=true&characterEncoding=UTF-8
user=root
password=2411030483
UserDao.java--定义功能
package bean2;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;
public class UserDao {
public int getPageCount() throws Exception{
int recordCount=0,t1=0,t2=0;
Connection conn=JdbcUtil.getConnection();
String sql="select count(*) from student";
PreparedStatement pstmt=conn.prepareStatement(sql);
ResultSet rs=pstmt.executeQuery();
rs.next();
recordCount=rs.getInt(1);
t1=recordCount%5;
t2=recordCount/5;
JdbcUtil.free(conn, pstmt, rs);
return t1==0?t2:t2+1;
}
public List<User> listUser(int pageNo) throws Exception{
int pageSize=5;
int startRecno=(pageNo-1)*pageSize;
ArrayList<User> userList=new ArrayList<User>();
Connection conn=JdbcUtil.getConnection();
String sql="select * from student order by id limit ?,?";
PreparedStatement pstmt=conn.prepareStatement(sql);
pstmt.setInt(1,startRecno);
pstmt.setInt(2, pageSize);
ResultSet rs=pstmt.executeQuery();
while(rs.next()){
User user=new User();
user.setId(rs.getString(1));
user.setName(rs.getString(2));
user.setSex(rs.getString(3));
userList.add(user);
}
JdbcUtil.free(conn, pstmt, rs);
return userList;
}
}
page.java--servlet类,用以完成最终的功能调用
package bean2;
import java.io.IOException;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class page
*/
@WebServlet("/page")
public class page extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public page() {
super();
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
int pageNo=1;
int pagesize=1;
String strPageNo=request.getParameter("pageNo");
if(strPageNo!=null){
pageNo=Integer.parseInt(strPageNo);
}
UserDao userDao=new UserDao();
try {
List<User> userlist=userDao.listUser(pageNo);
request.setAttribute("userlist", userlist);
Integer pageCount=new Integer(userDao.getPageCount());
request.setAttribute("pageCount", pageCount);
request.setAttribute("pageNo", pageNo);
request.getRequestDispatcher("userlist.jsp").forward(request, response);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
tiaozhuan.jsp--跳转页面,可以不使用,如果不使用的话,需要直接运行servlet类,来获取页面
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>跳转页面</title>
</head>
<body>
<p>跳转页面</p>
<hr>
<form action="page" method="post">
<table><tr><td>
<input type="submit" value="发送"></td><td>
<input type="reset" value="取消">
</td></tr>
</table>
</form>
</body>
</html>
userlist.jsp--显示页面
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>用户列表</title>
<style>
th,td{width:150px;border:2px solid gray;text-align:center;padding:2px 10px;}
table{border-collapse:collapse;}
body{text-align:center;}
a{text-decoration:none;}
</style>
</head>
<body>
<c:if test="${pageCount>0}">
<h2>所有用户信息</h2>
共有${pageCount}页,这是第${pageNo}页
<c:if test="${pageNo>1}">
<a href="page?pageNo=1">第一页</a>
<a href="page?pageNo=${pageNo-1}">上一页</a>
</c:if>
<c:if test="${pageNo!=pageCount}">
<a href="page?pageNo=${pageNo+1}">下一页</a>
<a href="page?pageNo=${pageCount}">最后一页</a>
</c:if>
<table align="center">
<tr><th>用户编号</th><th>用户名</th><th>性别</th></tr>
<c:forEach items="${userlist }" var="user">
<tr><td>${user.id }</td><td>${user.name }</td><td>${user.sex }</td></tr>
</c:forEach>
</table>
<br>
</c:if>
<c:if test="${pageCount==0}">
<p>目前没有记录</p>
</c:if>
</body>
</html>