JDBC——用Java在数据库中创建一个Student表

一、Studnet表：

属性：sno int(20)、cno int(4)、grade int(4)。即学号、课程号、成绩。

二、Java中的类

用到的类: DBUtil(连接、关闭数据库)、Student(学生信息)、Userdemo(接口：实现Student表的增删该查)、UserdemoImpl(实现Userdemo接口里的方法)、Test(测试台)；

1、Student

//Student表
public class Student
{
	private int sno;
	private int cno;
	private int grade;
	
	public Student(int sno, int cno, int grade)
	{
		this.sno = sno;
		this.cno = cno;
		this.grade = grade;
	}

	public Student()
	{
		
	}
	
	public String toString()
	{
		return this.sno+","+this.cno+","+this.grade;
	}

	public int getSno()
	{
		return sno;
	}

	public void setSno(int sno)
	{
		this.sno = sno;
	}

	public int getCno()
	{
		return cno;
	}

	public void setCno(int cno)
	{
		this.cno = cno;
	}

	public int getGrade()
	{
		return grade;
	}

	public void setGrade(int grade)
	{
		this.grade = grade;
	}
	
}

2、DBUtil

import java.io.*;
import java.util.*;
import java.sql.*;

public class DBUtil
{
	
	private static String driver = "com.mysql.cj.jdbc.Driver";   //用于加载驱动
	private static String url = "jdbc:mysql://localhost:3306/sc3?serverTimezone=UTC";  //数据库地址
	private static String username = "root";  //用户名
	private static String password = "123456";   //密码
	
	//连接数据库
	public static Connection open()
	{
		try
		{
			Class.forName(driver);    //加载驱动
			return DriverManager.getConnection(url, username, password);
		} catch (Exception e)
		{
			e.printStackTrace();
		}
		return null;
	}
	
	//关闭数据库
	public static void close(Connection conn)
	{
		if(conn!=null)
		{
			try
			{
				conn.close();
			} catch (SQLException e)
			{
				e.printStackTrace();
			}
		}
	}

}

3、Userdemo

import java.util.ArrayList;

//实现对数据库中sc表的增、删、改、查
public interface Userdemo
{
	public void Insert(Student s);
	
	public void Delete(int sno,int cno);
	
	public void Update(Student s);
	
	public Student Get(int sno,int cno);
	
	public ArrayList<Student> SelectAll();

}

4、UserdemoImpl

import java.util.*;
import java.sql.*;

public class UserdemoImpl implements Userdemo   //实现Userdemo接口的方法
{

	@Override
	public void Insert(Student s)   //增
	{
		//链接数据库
		Connection conn = DBUtil.open();
		//创建语句
		String sql = "insert into sc values(?,?,?)";
		try
		{
			//动态操作sql语句
			PreparedStatement pstmt = conn.prepareStatement(sql);
			pstmt.setInt(1,s.getSno());
			pstmt.setInt(2,s.getCno());
			pstmt.setInt(3,s.getGrade());
			pstmt.executeUpdate();
		} catch (SQLException e)
		{
			e.printStackTrace();
		}
		finally
		{
			DBUtil.close(conn);  //关闭数据库
		}
		
		
		
	}

	@Override
	public void Delete(int sno, int cno)   //删
	{
		Connection conn = DBUtil.open();
		String sql = "delete from sc where sno=? and cno=?";
		
		try
		{
			PreparedStatement pstmt = conn.prepareStatement(sql);
			pstmt.setInt(1,sno);
			pstmt.setInt(2,cno);
			pstmt.executeUpdate();
		} catch (SQLException e)
		{
			e.printStackTrace();
		}
		finally
		{
			DBUtil.close(conn);
		}
		
		
	}

	@Override
	public void Update(Student s)    //改
	{
		Connection conn = DBUtil.open();
		String sql = "update sc set grade=? where sno=? and cno=?";
		
		try
		{
			PreparedStatement pstmt = conn.prepareStatement(sql);
			pstmt.setInt(1,s.getGrade());
			pstmt.setInt(2,s.getSno());
			pstmt.setInt(3,s.getCno());
			pstmt.executeUpdate();
		} catch (Exception e)
		{
			e.printStackTrace();
		}
		finally
		{
			DBUtil.close(conn);
		}
		
	}

	@Override
	public Student Get(int sno, int cno)   //查
	{
		Connection conn = DBUtil.open();
		String sql = "select grade from sc where sno=? and cno=?";
		
		try
		{
			PreparedStatement pstmt = conn.prepareStatement(sql);
			pstmt.setInt(1,sno);
			pstmt.setInt(2,cno);
			ResultSet rs = pstmt.executeQuery();
			if(rs.next())
			{
				int grade = rs.getInt(1);
				Student s = new Student(sno,cno,grade);
				return s;
			}
		} catch (Exception e)
		{
			e.printStackTrace();
		}
		finally
		{
			DBUtil.close(conn);
		}
		
		return null;
	}

	@Override
	public ArrayList<Student> SelectAll()   //遍历
	{
		ArrayList<Student> stu = new ArrayList<Student>();
		Connection conn = DBUtil.open();
		String sql = "select * from sc";
		try
		{
			Statement stmt = conn.createStatement();
			ResultSet rs = stmt.executeQuery(sql);
			while(rs.next())
			{
				int sno = rs.getInt(1);
				int cno = rs.getInt(2);
				int grade = rs.getInt(3);
				Student s = new Student(sno,cno,grade);
				stu.add(s);
			}
			return stu;
		} catch (SQLException e)
		{
			e.printStackTrace();
		}
		finally
		{
			DBUtil.close(conn);
		}
		
		return null;
	}

}

5、Test

import java.util.*;
import java.sql.*;

public class Test
{
	
	public static void Create()    //创建Student表
	{
		Connection conn = DBUtil.open();  //连接数据库
		String sql = "create table student(sno int(20),cno int(4),grade int(4),primary key(sno,cno))";
		try
		{
			Statement stmt = conn.createStatement();  //静态操作sql语句
			stmt.execute(sql);
		} catch (SQLException e)
		{
			e.printStackTrace();
		}
		finally
		{
			DBUtil.close(conn);
		}
	}
	
	public static void show()  //提示信息
	{
		System.out.println("***********成绩数据库管理***********");
		System.out.println("insert: 插入成绩.");
		System.out.println("delete: 删除成绩.");
		System.out.println("update: 更新成绩.");
		System.out.println("get: 查看成绩.");
		System.out.println("list: 查看所有成绩.");
		System.out.println("***********成绩数据库管理***********");
	}

	public static void main(String[] args)
	{
		Scanner in = new Scanner(System.in);
//		Create();
		Userdemo userdemo = new UserdemoImpl();   //多态
		Student stu = new Student();
		while(true)
		{
			show();
			System.out.print("命令>");
			String s = in.next();
			if(s.equals("insert"))
			{
				System.out.println("请输入正确的信息，如果重复、不存在、信息错误，都会出现错误.");
				System.out.print("请输入学号：");
				int sno = in.nextInt();
				System.out.print("请输入课程号：");
				int cno = in.nextInt();
				System.out.print("请输入成绩：");
				int grade = in.nextInt();
				stu.setSno(sno);
				stu.setCno(cno);
				stu.setGrade(grade);
				userdemo.Insert(stu);
			}
			else if(s.equals("delete"))
			{
				System.out.println("请输入正确的信息，如果重复、不存在、信息错误，都会出现错误.");
				System.out.print("请输入待删除的学号：");
				int sno = in.nextInt();
				System.out.print("请输入待删除的课程号：");
				int cno = in.nextInt();
				userdemo.Delete(sno, cno);
			}
			else if(s.equals("update"))
			{
				System.out.println("请输入正确的信息，如果重复、不存在、信息错误，都会出现错误.");
				System.out.print("请输入待更新的学号：");
				int sno = in.nextInt();
				System.out.print("请输入待更新的课程号：");
				int cno = in.nextInt();
				System.out.print("请输入新成绩：");
				int grade = in.nextInt();
				stu.setSno(sno);
				stu.setCno(cno);
				stu.setGrade(grade);
				userdemo.Update(stu);
			}
			else if(s.equals("get"))
			{
				System.out.println("请输入正确的信息，如果重复、不存在、信息错误，都会出现错误.");
				System.out.print("请输入查询的学号：");
				int sno = in.nextInt();
				System.out.print("请输入查询的课程号：");
				int cno = in.nextInt();
				stu = userdemo.Get(sno, cno);
				System.out.println("成绩："+stu.getGrade());
			}
			else if(s.equals("list"))
			{
				ArrayList<Student> note = userdemo.SelectAll();
				for(int i=0,t=note.size();i<t;i++)
				{
					System.out.println(note.get(i));
				}
				
			}
			else if(s.equals("exit"))
			{
				System.out.println("再见！");
				System.exit(0);
			}
		}

	}

}