Java理论和实践：了解泛型和实例

技术2022-05-20 59

单态模式实现分页

步骤如下

首先，创建一个web项目例如：2011firstweb

其次，创建包命

创建所需包命如：

1.cn.csdn.domain(主要封装bean)

2.cn.csdn.util(工具类)

3，cn.csdn.web.dao(主要写dao方法)

4，cn.csdn.web.serivice(主要连接服务)

5.cn.csdn.web.servlet(主要封装请求)

三，进入编程阶段

1，创建一个连接数据库类如：DBConn

package cn.csdn.util;

import java.sql.DriverManager;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;

import com.mysql.jdbc.Connection;

public class DBConn { private static Connection conn; private DBConn(){} public static Connection getConn(){ if(conn==null){ try { Class.forName("com.mysql.jdbc.Driver"); try { conn=(Connection) DriverManager.getConnection("jdbc:mysql://localhost:3306/db?user=root&password=123&useUnicode=true&characterEncoding=utf8"); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } } catch (ClassNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } } return conn; } //关闭 public static void coles(ResultSet rs,PreparedStatement pstmt){ if(rs!=null){ try { rs.close(); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } } if(pstmt!=null){ try { pstmt.close(); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } } } public static void main(String[] args) { DBConn.getConn(); }

} 2.封装数据

package cn.csdn.domain;

public class Student { public Student() { }

public Student(String name, int age, String email) { this.name=name; this.age=age; this.email=email; }

private int id; private String name; private String email; private int age; 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 getEmail() { return email; }

public void setEmail(String email) { this.email = email; }

public int getAge() { return age; }

public void setAge(int age) { this.age = age; }

}

3.写DAO方法

接口类

package cn.csdn.web.dao;

import java.util.List;

import cn.csdn.domain.Student;

public interface StudentDao { int getCountRecord(); int getCountPage(); List<Student> getNowPageInfo(int nowpage);

} 方法

package cn.csdn.web.dao;

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 cn.csdn.domain.Student;import cn.csdn.util.DBConn;

public class StudentDaoImpl implements StudentDao { private Connection conn; private PreparedStatement pstmt; private ResultSet rs; private static final int PAGESIZE = 5;

// 获取总页数 public int getCountPage() {

return getCountRecord() % PAGESIZE == 0 ? getCountRecord() / PAGESIZE : getCountRecord() / PAGESIZE + 1; }

// 获取总信息 public int getCountRecord() { // 定义返回变量 int countrecord = 0; // 创建数据库连接 conn = DBConn.getConn(); // String sql = "select count(*) from student"; try { pstmt = conn.prepareStatement(sql); rs = pstmt.executeQuery(); if (rs.next()) { countrecord = rs.getInt(1);

} } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } finally {

DBConn.coles(rs, pstmt); }

return countrecord; }

public List<Student> getNowPageInfo(int nowpage) { List<Student> allentities = new ArrayList<Student>(); conn = DBConn.getConn(); String sql = "select id,name,age,email from student limit ?,?"; try { pstmt = conn.prepareStatement(sql); int index = 1; pstmt.setInt(index++, (nowpage-1)*PAGESIZE); pstmt.setInt(index++, PAGESIZE); rs = pstmt.executeQuery(); while (rs.next()) { Student entity = new Student(); entity.setId(rs.getInt("id")); entity.setAge(rs.getInt("age")); entity.setName(rs.getString("name")); entity.setEmail(rs.getString("email")); allentities.add(entity);

} } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); }finally{ DBConn.coles(rs, pstmt); } return allentities; } public static void main(String[] args) { StudentDaoImpl sdi = new StudentDaoImpl(); /* int countecord=sdi.getCountRecord(); System.out.println(countecord); System.out.println(sdi.getCountPage());*/ List<Student> allentities=sdi.getNowPageInfo(2); for(Student entity:allentities){ System.out.println(entity.getAge()); } }} 4，连接服务

服务接口

package cn.csdn.web.service;

import java.util.List;

import cn.csdn.domain.Student;

public interface StudentService { int getCountRecord(); //获取总页数 int getCountPage(); //获取当前页的信息 List<Student> getNowPageInfo(int nowpage);} 方法

package cn.csdn.web.service;

import java.util.List;

import cn.csdn.domain.Student;import cn.csdn.web.dao.StudentDaoImpl;

public class StudentServiceImpl implements StudentService { private StudentDaoImpl sdi = new StudentDaoImpl();

public int getCountPage() { // TODO Auto-generated method stub System.out.println("-----"); return sdi.getCountPage(); }

public int getCountRecord() { // TODO Auto-generated method stub return sdi.getCountRecord(); }

public List<Student> getNowPageInfo(int nowpage) { // TODO Auto-generated method stub return sdi.getNowPageInfo(nowpage); }

public static void main(String[] args) { StudentServiceImpl ass=new StudentServiceImpl(); ass.getCountPage(); }}5，封装请求

package cn.csdn.web.servlet;

import java.io.IOException;import java.util.List;

import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;

import cn.csdn.domain.Student;import cn.csdn.web.service.StudentServiceImpl;

public class ListStudentsServlet extends HttpServlet {

/** * */ private static final long serialVersionUID = 4438133059395214446L;

@Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { this.doPost(req, resp); }

@Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { //1、设置编码 req.setCharacterEncoding("UTF-8"); //2、获取当前页 //定义当前页的变量 int nowpage =1; String npage = req.getParameter("nowpage"); if(npage!=null){ nowpage = Integer.parseInt(npage); } //3、创业业务操作的实现类的对象 StudentServiceImpl ssi = new StudentServiceImpl(); int lastpage = ssi.getCountPage(); List<Student> allentities = ssi.getNowPageInfo(nowpage); //存入当前页最后一页当前页的记录信息 req.setAttribute("nowpage", nowpage); req.setAttribute("lastpage", lastpage); req.setAttribute("allentities", allentities); req.getRequestDispatcher("fend.jsp").forward(req, resp); }

}

6，创建JSP/HTML

<%@ 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 'index.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">  </head> <body> <h1><a href="listStudents.do">查询所有学生信息</a></h1> </body></html>

跳转页面

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %><%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 'sc.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">

</head> <body> <div align="center"> <h1>显示所有的学员信息</h1> <table border="1px" cellpadding="0" cellspacing="0"> <caption>学员信息</caption> <tr> <th>全选</th> <th>序列</th> <th>姓名</th> <th>年龄</th> <th>邮箱</th> <th>操作</th> </tr> <c:forEach items="${allentities}" var="entity"> <tr> <td><input type="checkbox" name="chk"/></td> <td>${entity.id}</td> <td>${entity.name}</td> <td>${entity.age}</td> <td>${entity.email}</td> <td>编辑|删除</td> </tr> </c:forEach> </table> <div> <span><a href="./listStudents.do?nowpage=1">首页</a></span> <span><a href="./listStudents.do?nowpage=${nowpage-1}">上一页</a></span> <span><a href="./listStudents.do?nowpage=${nowpage+1}">下一页</a></span> <span><a href="./listStudents.do?nowpage=${lastpage}">最后一页</a></span> </div> </div> </body></html>

创建数据库

/*Column Information For - db.student*/---------------------------------------

Field Type Collation Null Key Default Extra Privileges Comment------ ----------- --------------- ------ ------ ------- -------------- ------------------------------- -------id int(11) (NULL) NO PRI (NULL) auto_increment select,insert,update,references name varchar(40) utf8_general_ci YES (NULL) select,insert,update,references age int(11) (NULL) YES (NULL) select,insert,update,references email varchar(50) utf8_general_ci YES (NULL) select,insert,update,references

/*Index Information For - db.student*/--------------------------------------

Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Null Index_type Comment------- ---------- -------- ------------ ----------- --------- ----------- -------- ------ ------ ---------- -------student 0 PRIMARY 1 id A 19 (NULL) (NULL) BTREE

/*DDL Information For - db.student*/------------------------------------

Table Create Table ------- -----------------------------------------student CREATE TABLE `student` ( `id` int(11) NOT NULL auto_increment, `name` varchar(40) default NULL, `age` int(11) default NULL, `email` varchar(50) default NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8

7，发布启动服务

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