本文通过两个方法:(1)计算总的页数。 (2)查询指定页数据,实现简单的分页效果。
思路:首先得在 DAO 对象中提供分页查询的方法,在控制层调用该方法查到指定页的数据,在表示层通过 EL 表达式和 JSTL 将该页数据显示出来。
先给大家展示下效果图:
题外话:该分页显示是用 “表示层-控制层-DAO层-数据库”的设计思想实现的,有什么需要改进的地方大家提出来,共同学习进步。废话不多说了,开始进入主题,详细步骤如下所示:
1.DAO层-数据库
JDBCUtils 类用于打开和关闭数据库,核心代码如下:
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import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
public class JDBCUtils {
private Connection conn= null ;
private PreparedStatement pstmt= null ;
/**
* connect 连接数据库
* @return
*/
public Connection connect(){
String user= "root" ;
String password= "1234" ;
String driverClass = "com.mysql.jdbc.Driver" ;
String jdbcUrl = "jdbc:mysql://localhost:3306/book" ;
try {
Class.forName(driverClass);
conn = DriverManager.getConnection(jdbcUrl, user, password);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return conn;
}
/**
* close 关闭数据库
* @param conn
* @param pstmt
* @param resu
*/
public void close(Connection conn,PreparedStatement pstmt,ResultSet result){
if (conn != null ){
try {
conn.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
}
}
if (pstmt != null ){
try {
pstmt.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if (result != null ){
try {
result.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
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UserDao 类中的方法 getPage() 和方法 listUser() 分别用来计算总页数和查询指定页的数据,核心代码如下:
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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 com.db.JDBCUtils;
public class UserDao {
/**
* 计算总的页数
* @return
*/
public int getPage(){
int recordCount= 0 ,t1= 0 ,t2= 0 ;
PreparedStatement pstmt= null ;
ResultSet result= null ;
JDBCUtils jdbc= new JDBCUtils();
Connection conn=jdbc.connect();
String sql= "select count(*) from books" ;
try {
pstmt=conn.prepareStatement(sql);
result=pstmt.executeQuery();
result.next();
recordCount=result.getInt( 1 );
t1=recordCount% 5 ;
t2=recordCount/ 5 ;
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
jdbc.close(conn, pstmt, result);
}
if (t1 != 0 ){
t2=t2+ 1 ;
}
return t2;
}
/**
* 查询指定页的数据
* @param pageNo
* @return
*/
public List<User> listUser( int pageNo){
PreparedStatement pstmt= null ;
ResultSet result= null ;
List<User> list= new ArrayList<User>();
int pageSize= 5 ;
int page=(pageNo- 1 )* 5 ;
JDBCUtils jdbc= new JDBCUtils();
Connection conn=jdbc.connect();
String sql= "select * from books order by id limit ?,?" ;
try {
pstmt=conn.prepareStatement(sql);
pstmt.setInt( 1 , page);
pstmt.setInt( 2 , pageSize);
result=pstmt.executeQuery();
while (result.next()){
User user= new User();
user.setId(result.getInt( 1 ));
user.setName(result.getString( 2 ));
user.setNumber(result.getString( 3 ));
list.add(user);
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
jdbc.close(conn, pstmt, result);
}
return list;
}
}
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User 类用于存储查询到的数据,核心代码如下:
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public class User {
private int id;
private String name;
private String number;
public int getId() {
return id;
}
public void setId( int id) {
this .id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this .name = name;
}
public String getNumber() {
return number;
}
public void setNumber(String number) {
this .number = number;
}
}
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2.控制层
ListUser 类内部调用 UserDao 对象查询数据并指派页面显示数据,核心代码如下:
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import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.dao.User;
import com.dao.UserDao;
public class ListUser extends HttpServlet {
public ListUser() {
super ();
}
public void destroy() {
super .destroy(); // Just puts "destroy" string in log
// Put your code here
}
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doPost(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setCharacterEncoding( "utf-8" );
int pageNo = 1 ;
UserDao userdao= new UserDao();
List<User> lists= new ArrayList<User>();
String pageno=request.getParameter( "pageNos" );
if (pageno != null ){
pageNo=Integer.parseInt(pageno);
}
lists=userdao.listUser(pageNo);
int recordCount=userdao.getPage();
request.setAttribute( "recordCount" , userdao.getPage());
request.setAttribute( "listss" , lists);
request.setAttribute( "pageNos" , pageNo);
request.getRequestDispatcher( "userlist.jsp" ).forward(request, response);
}
public void init() throws ServletException {
// Put your code here
}
}
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3.表示层
输出页面 userlist.jsp ,使用 EL 和 JSTL 输出查询结果,核心代码如下:
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<%@ page language= "java" import = "java.util.*" pageEncoding= "UTF-8" %>
<%@ taglib prefix= "c" uri= "http://java.sun.com/jsp/jstl/core" %>
<%@ taglib uri= "http://java.sun.com/jsp/jstl/fmt" prefix= "fmt" %>
<%@ taglib uri= "http://java.sun.com/jsp/jstl/functions" prefix= "fn" %>
<%
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 'userlist.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" >
-->
<style type= "text/css" >
th,td{width: 150px;border: 2px solid gray;text-align: center;}
body{text-align: center;}
a{text-decoration: none;}
table {border-collapse: collapse;}
</style>
</head>
<body>
<h2 align= "center" >图书信息</h2>
<table align= "center" >
<tr><td>书号</td><td>书名</td><td>库存量</td></tr>
</table>
<table align= "center" >
<c:forEach items= "${listss}" var= "person" >
<tr>
<td class = "hidden-480" >${person.id}</td>
<td class = "hidden-480" >${person.name }</td>
<td class = "hidden-480" >${person.number }</td>
</tr>
</c:forEach>
</table>
<br>
<c: if test= "${pageNos>1 }" >
<a href= "ListUser?pageNos=1" >首页</a>
<a href= "ListUser?pageNos=${pageNos-1 }" >上一页</a>
</c: if >
<c: if test= "${pageNos <recordCount }" >
<a href= "ListUser?pageNos=${pageNos+1 }" >下一页</a>
<a href= "ListUser?pageNos=${recordCount }" >末页</a>
</c: if >
<form action= "ListUser" >
<h4 align= "center" >共${recordCount}页
<input type= "text" value= "${pageNos}" name= "pageNos" size= "1" >页
<input type= "submit" value= "到达" >
</h4>
</form>
</body>
</html>
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以上所述是小编给大家介绍的Java Web 简单的分页显示实例代码,希望对大家有所帮助,如果大家有任何疑问请给我留言,小编会及时回复大家的。在此也非常感谢大家对服务器之家网站的支持!