2020年11月4日Java学习日记

课程管理系统的增删改查

1、连接数据库

要连接数据库，首先得建立一个数据库表，建立表头信息。然后在eclipse里进行操作。

在util 层下建立 DBUtil.java 文件，将数据库连接。主要分为四步：

  • 加载驱动程序
  • 数据库连接字符串
  • 数据库登录名和密码
  • 关闭数据库
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package util;

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

public class DBUtil {

    public  static  Connection getConnection() {
        try {
            Class.forName("com.mysql.jdbc.Driver").newInstance();
        } catch (InstantiationException | IllegalAccessException | ClassNotFoundException e) {
            e.printStackTrace();
        }
        String user = "root";
        String password = "liutianwen0613";
        String url = "jdbc:mysql://localhost:3306/login? ?characterEncoding=utf-8&useSSL=true";
        Connection connection = null;
        try {
             connection = DriverManager.getConnection(url,user,password);
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return connection;
    }

    public static void close(Connection connection ) {
        try {
            if (connection != null) {
                connection.close();
            }

        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    public static void close(PreparedStatement preparedStatement ) {
        try {
            if (preparedStatement != null) {
                preparedStatement.close();
            }

        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    public static void close(ResultSet resultSet ) {
        try {
            if (resultSet != null) {
                resultSet.close();
            }

        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

}
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2、在 bean 层下建 infor.java 文件,里面创建对象，属性为 private。然后分别建立 set 和 get 函数，属性为 public（可通过右击--源码快速生成）

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package bean;

public class infor{
    private String name;
    private String teacher;
    private String address;
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getTeacher() {
        return teacher;
    }
    public void setTeacher(String teacher) {
        this.teacher = teacher;
    }
    public String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    }

    public infor() {}

    public infor(String name,String teacher,String address) {
        this.name = name;
        this.teacher = teacher;
        this.address = address;
    }

}
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注意：必须要有一个空的构造函数

3、在dao层下建立studentdao.java文件，专门写对数据库的操作，在里面写增删改查的函数，根据功能来写不同的函数，每个函数都得调用数据库的连接语句：

Connection connection = DBUtil.getConnection();　

用到对数据库操作的语句：

    String sql = "select count(*) from class1 where name = ?";//选择语句

    sql = "insert into class1(name,teacher,address) value (?,?,?)";//插入语句

语句有很多种，基本用法也不尽相同。

同时还得新定义这两个语句:

    PreparedStatement preparedStatement = null;

    ResultSet resultSet = null;

然后就是写函数体。根据不同的要求写不同的函数。

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package dao;
 
import javax.swing.*;
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 util.DBUtil;
import bean.infor;
 
 
public class studentdao {
 
    public void add1(String name, String teacher,String address) {
 
        Connection connection = DBUtil.getConnection();
 
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        try {
            String sql = "insert into class1(name,teacher,addess) value (?,?,?)";
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1, name);
            preparedStatement.setString(2, teacher);
            preparedStatement.setString(3, address);
            preparedStatement.executeUpdate();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            DBUtil.close(resultSet);
            DBUtil.close(preparedStatement);
            DBUtil.close(connection);
        }
 
    }
 
 
    public void update(String name, String newname,String newteacher,String newaddress) {
        Connection connection = DBUtil.getConnection();
 
        String sql = "select count(*) from class1 where name = ?";
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        try {
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1, name);
            resultSet = preparedStatement.executeQuery();
            while (resultSet.next()) {
                if (resultSet.getInt(1) > 0)
                {
                    System.out.println("开始修改");
                    sql = "update class1 set name=?,teacher=?,address=?  where name=?";
                    preparedStatement = connection.prepareStatement(sql);
                    preparedStatement.setString(1, newname);
                    preparedStatement.setString(2, newteacher);
                    preparedStatement.setString(3, newaddress);
                    preparedStatement.setString(4, name);
                } preparedStatement.executeUpdate();
        }
            } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            DBUtil.close(resultSet);
            DBUtil.close(preparedStatement);
            DBUtil.close(connection);
        }
 
    }
 
    public void delete(String username) {
        Connection connection = DBUtil.getConnection();
        String sql = "delete from class1 where name = ?";
        PreparedStatement preparedStatement = null;
 
        try {
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1, username);
            preparedStatement.executeUpdate();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            DBUtil.close(preparedStatement);
            DBUtil.close(connection);
        }
 
    }
 
    public int add(String name,String teacher,String address) {
 
        Connection connection = DBUtil.getConnection();
 
        String sql = "select count(*) from class1 where name = ?";
 
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        try {
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1, name);
 
            resultSet = preparedStatement.executeQuery();
 
            System.out.println("hello");
            while(resultSet.next()) {
                if (resultSet.getInt(1) > 0)
                {
 
                    return 0;
                }
 
                else
                {
                    sql = "insert into class1(name,teacher,address) value (?,?,?)";
                    preparedStatement = connection.prepareStatement(sql);
                    preparedStatement.setString(1, name);
                    preparedStatement.setString(2, teacher);
                    preparedStatement.setString(3, address);
                    preparedStatement.executeUpdate();
                    return 1;
                }
                }
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            //e.printStackTrace();
            e.getMessage();
        }finally {
 
            DBUtil.close(resultSet);
            DBUtil.close(preparedStatement);
            DBUtil.close(connection);
        }
        return 0;
 
    }
 
    public int load(String name) {
        // TODO Auto-generated method stub
 
        Connection connection = DBUtil.getConnection();
        String sql = "select * from class1 where name = ?";
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        try {
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1, name);
            resultSet = preparedStatement.executeQuery();
            while (resultSet.next()) {
                System.out.println("课程名称：" + resultSet.getString("name"));
                System.out.println("任课教师：" + resultSet.getString("teacher"));
                System.out.println("上课地点：" + resultSet.getString("address"));
                return 1;
            }
 
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            DBUtil.close(resultSet);
            DBUtil.close(preparedStatement);
            DBUtil.close(connection);
        }
        return 0;
    }
    public String load_del(String name) {
        // TODO Auto-generated method stub
        Connection connection = DBUtil.getConnection();
        String sql = "select * from class1 where name = ?";
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        try {
 
            preparedStatement = connection.prepareStatement(sql);
            preparedStatement.setString(1, name);
            resultSet = preparedStatement.executeQuery();
            while (resultSet.next()) {
                System.out.println("课程名称：" + resultSet.getString("name"));
                System.out.println("任课教师：" + resultSet.getString("teacher"));
                System.out.println("上课地点：" + resultSet.getString("address"));
                return ("课程名称：" + resultSet.getString("name")+"      任课教师：" + resultSet.getString("teacher")+"        上课地点：" + resultSet.getString("address"));
            }
 
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            DBUtil.close(resultSet);
            DBUtil.close(preparedStatement);
            DBUtil.close(connection);
        }
        return "课程不存在！";
    }
 
    public String load_delete(String name) {
        // TODO Auto-generated method stub
        Connection connection = DBUtil.getConnection();
        //System.out.println(111);
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        try {
            String sql = "select * from class1 where name like '%"+name+"%'";
            preparedStatement = connection.prepareStatement(sql);
            resultSet = preparedStatement.executeQuery();
            while (resultSet.next()) {
                System.out.println("课程名称：" + resultSet.getString("name"));
                System.out.println("任课教师：" + resultSet.getString("teacher"));
                System.out.println("上课地点：" + resultSet.getString("address"));
                return ("课程名称：" + resultSet.getString("name")+"      任课教师：" + resultSet.getString("teacher")+"        上课地点：" + resultSet.getString("address"));
            }
 
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            DBUtil.close(resultSet);
            DBUtil.close(preparedStatement);
            DBUtil.close(connection);
        }
        return "课程不存在！";
    }
 
 
    public List<infor> loadlist(String name,String teacher,String address) {
        // TODO Auto-generated method stub
        String sql = "select * from class1 where ";
        if (name != "") {
            sql += "name like '%" + name + "%'";
        }
        if (teacher != "") {
            sql += "teacher like '%" + teacher + "%'";
        }
        if (address != "") {
            sql += "classroom like '%" + address + "%'";
        }
        List<infor> list = new ArrayList<>();
        Connection connection = DBUtil.getConnection();
        //System.out.println(111);
        infor bean = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        try {
            //String sql = "select * from class1 where name like '%"+name+"%'";
            preparedStatement = connection.prepareStatement(sql);
            resultSet = preparedStatement.executeQuery();
            while (resultSet.next()) {
                String name2 = resultSet.getString("name");
                String teacher2 = resultSet.getString("teacher");
                String address2 = resultSet.getString("address");
                bean = new infor(name2,teacher2,address2);
                list.add(bean);
                System.out.println("课程名称：" + resultSet.getString("name"));
                System.out.println("任课教师：" + resultSet.getString("teacher"));
                System.out.println("上课地点：" + resultSet.getString("address"));
                //return ("课程名称：" + resultSet.getString("name")+"      任课教师：" + resultSet.getString("teacher")+"        上课地点：" + resultSet.getString("address"));
            }
 
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            DBUtil.close(resultSet);
            DBUtil.close(preparedStatement);
            DBUtil.close(connection);
        }
        return list;
    }
}

4、搭建界面

主要用的是jsp，先建立一个主页，展示操作，再分别建立增删改查的jsp：

然后在jsp里面进行传值，调用Java文件的函数，进而操作数据库。

这些jsp文件里并不是都是显示页面，有一些只是进行判断的页面，调用函数进行操作数据库。

这是主页面，分成了上左右三块，左边菜单栏，上边是名称，右边是各种操作界面及结果显示。

代码：

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 1 <%@ page language="java" contentType="text/html; charset=utf-8"
 2     pageEncoding="utf-8"%>
 3 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 4 <html>
 5 <head>
 6 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
 7 <title>主页</title>
 8 <link rel="stylesheet" href="css/page.css" />
 9 <script type="text/javascript" src="js/jquery.min.js"></script>
10 <script type="text/javascript" src="js/index.js"></script>
11 </head>
12 
13 <frameset rows="20%,*">
14 <frame class="top" src="top.jsp">
15 <frameset cols="20%,*">
16 <frame src="main_left.jsp">
17 <frame src="main_right.jsp" name="main_right">
18 </frameset>
19 </frameset>
20 <body>
21 
22 </body>
23 </html>
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其他分界面以添加为例

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 1 <%@ page language="java" contentType="text/html; charset=utf-8"
 2     pageEncoding="utf-8"%>
 3     <%@ page import="com.jaovo.msg.dao.*" %>
 4 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 5 <html>
 6 <head>
 7 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
 8 <title>Insert title here</title>
 9 </head>
10 <body>
11 <form method="post" action="inputstuinfo_result.jsp">
12 
13 <div align="center">
14 <h5>课程名称：<input name="input_name" type="text" placeholder="请输课程名称"></h5>
15 <h5>任课教师：<input name="input_teacher" type="text" placeholder="请输任课教师"></h5>
16 <h5>上课地点：<input name="input_address" type="text" placeholder="请输上课地点"></h5>
17 <input name="submit" type="submit" >
18 </div>
19 </form>
20 </body>
21 </html>
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原文地址：https://www.cnblogs.com/9635741zly/p/14176463.html