四、在 eclipse 平台中，通过 jdbc 建立动态网站到数据库的连接类 DBConnect； 并建立 StudentDAO 完成应用程序对数据库的增删改查操作；并建立 CourseDAO 完成应用程序对数据库的增删改查操作；建立 ScoreDAO 完成应用程序对数据库 的增删改查操作。

好的，根据您的要求，我来为您编写建立动态网站到数据库的连接类DBConnect、StudentDAO、CourseDAO和ScoreDAO的Java代码：

1. DBConnect类：

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

public class DBConnect {
    private static final String URL = "jdbc:mysql://localhost:3306/stuDB?useSSL=false&serverTimezone=UTC";
    private static final String USER = "root";
    private static final String PASSWORD = "123456";

    // 获取数据库连接
    public static Connection getConnection() {
        Connection conn = null;
        try {
            // 加载驱动
            Class.forName("com.mysql.cj.jdbc.Driver");
            // 获取连接
            conn = DriverManager.getConnection(URL, USER, PASSWORD);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return conn;
    }
}

2. StudentDAO类：

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

public class StudentDAO {
    private Connection conn = null;
    private PreparedStatement pstmt = null;
    private ResultSet rs = null;

    // 查询所有学生信息
    public List<Student> findAll() {
        List<Student> list = new ArrayList<Student>();
        try {
            conn = DBConnect.getConnection();
            String sql = "SELECT * FROM StuInfo";
            pstmt = conn.prepareStatement(sql);
            rs = pstmt.executeQuery();
            while (rs.next()) {
                Student stu = new Student();
                stu.setXhao(rs.getInt("xhao"));
                stu.setXming(rs.getString("xming"));
                stu.setXbie(rs.getString("xbie"));
                stu.setBji(rs.getString("bji"));
                list.add(stu);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            closeAll();
        }
        return list;
    }

    // 根据学号查询学生信息
    public Student findByXhao(int xhao) {
        Student stu = null;
        try {
            conn = DBConnect.getConnection();
            String sql = "SELECT * FROM StuInfo WHERE xhao=?";
            pstmt = conn.prepareStatement(sql);
            pstmt.setInt(1, xhao);
            rs = pstmt.executeQuery();
            if (rs.next()) {
                stu = new Student();
                stu.setXhao(rs.getInt("xhao"));
                stu.setXming(rs.getString("xming"));
                stu.setXbie(rs.getString("xbie"));
                stu.setBji(rs.getString("bji"));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            closeAll();
        }
        return stu;
    }

    // 添加学生信息
    public boolean add(Student stu) {
        boolean flag = false;
        try {
            conn = DBConnect.getConnection();
            String sql = "INSERT INTO StuInfo(xhao,xming,xbie,bji) VALUES(?,?,?,?)";
            pstmt = conn.prepareStatement(sql);
            pstmt.setInt(1, stu.getXhao());
            pstmt.setString(2, stu.getXming());
            pstmt.setString(3, stu.getXbie());
            pstmt.setString(4, stu.getBji());
            int count = pstmt.executeUpdate();
            if (count > 0) {
                flag = true;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            closeAll();
        }
        return flag;
    }

    // 修改学生信息
    public boolean update(Student stu) {
        boolean flag = false;
        try {
            conn = DBConnect.getConnection();
            String sql = "UPDATE StuInfo SET xming=?,xbie=?,bji=? WHERE xhao=?";
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, stu.getXming());
            pstmt.setString(2, stu.getXbie());
            pstmt.setString(3, stu.getBji());
            pstmt.setInt(4, stu.getXhao());
            int count = pstmt.executeUpdate();
            if (count > 0) {
                flag = true;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            closeAll();
        }
        return flag;
    }

    // 删除学生信息
    public boolean delete(int xhao) {
        boolean flag = false;
        try {
            conn = DBConnect.getConnection();
            String sql = "DELETE FROM StuInfo WHERE xhao=?";
            pstmt = conn.prepareStatement(sql);
            pstmt.setInt(1, xhao);
            int count = pstmt.executeUpdate();
            if (count > 0) {
                flag = true;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            closeAll();
        }
        return flag;
    }

    // 关闭连接
    private void closeAll() {
        try {
            if (rs != null) {
                rs.close();
            }
            if (pstmt != null) {
                pstmt.close();
            }
            if (conn != null) {
                conn.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

3. CourseDAO类：

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

public class CourseDAO {
    private Connection conn = null;
    private PreparedStatement pstmt = null;
    private ResultSet rs = null;

    // 查询所有课程信息
    public List<Course> findAll() {
        List<Course> list = new ArrayList<Course>();
        try {
            conn = DBConnect.getConnection();
            String sql = "SELECT * FROM CourseInfo";
            pstmt = conn.prepareStatement(sql);
            rs = pstmt.executeQuery();
            while (rs.next()) {
                Course course = new Course();
                course.setKcbma(rs.getString("kcbma"));
                course.setKcming(rs.getString("kcming"));
                course.setXfen(rs.getInt("xfen"));
                list.add(course);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            closeAll();
        }
        return list;
    }

    // 根据课程编号查询课程信息
    public Course findByKcbma(String kcbma) {
        Course course = null;
        try {
            conn = DBConnect.getConnection();
            String sql = "SELECT * FROM CourseInfo WHERE kcbma=?";
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, kcbma);
            rs = pstmt.executeQuery();
            if (rs.next()) {
                course = new Course();
                course.setKcbma(rs.getString("kcbma"));
                course.setKcming(rs.getString("kcming"));
                course.setXfen(rs.getInt("xfen"));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            closeAll();
        }
        return course;
    }

    // 添加课程信息
    public boolean add(Course course) {
        boolean flag = false;
        try {
            conn = DBConnect.getConnection();
            String sql = "INSERT INTO CourseInfo(kcbma,kcming,xfen) VALUES(?,?,?)";
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, course.getKcbma());
            pstmt.setString(2, course.getKcming());
            pstmt.setInt(3, course.getXfen());
            int count = pstmt.executeUpdate();
            if (count > 0) {
                flag = true;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            closeAll();
        }
        return flag;
    }

    // 修改课程信息
    public boolean update(Course course) {
        boolean flag = false;
        try {
            conn = DBConnect.getConnection();
            String sql = "UPDATE CourseInfo SET kcming=?,xfen=? WHERE kcbma=?";
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, course.getKcming());
            pstmt.setInt(2, course.getXfen());
            pstmt.setString(3, course.getKcbma());
            int count = pstmt.executeUpdate();
            if (count > 0) {
                flag = true;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            closeAll();
        }
        return flag;
    }

    // 删除课程信息
    public boolean delete(String kcbma) {
        boolean flag = false;
        try {
            conn = DBConnect.getConnection();
            String sql = "DELETE FROM CourseInfo WHERE kcbma=?";
            pstmt = conn.prepareStatement(sql);
            pstmt.setString(1, kcbma);
            int count = pstmt.executeUpdate();
            if (count > 0) {
                flag = true;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            closeAll();
        }
        return flag;
    }

    // 关闭连接
    private void closeAll() {
        try {
            if (rs != null) {
                rs.close();
            }
            if (pstmt != null) {
                pstmt.close();
            }
            if (conn != null) {
                conn.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

4. ScoreDAO类：

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

public class ScoreDAO {
    private Connection conn = null;
    private PreparedStatement pstmt = null;
    private ResultSet rs = null;

    // 查询所有成绩信息
    public List<Score> findAll() {
        List<Score> list = new ArrayList<Score>();
        try {
            conn = DBConnect.getConnection();
            String sql = "SELECT * FROM ScoreInfo";
            pstmt = conn.prepareStatement(sql);
            rs = pstmt.executeQuery();
            while (rs.next()) {
                Score score = new Score();
                score.setXhao(rs.getInt("xhao"));
                score.setKcbma(rs.getString("kcbma"));
                score.setXqi(rs.getInt("xqi"));
                score.setCji(rs.getInt("cji"));
                list.add(score);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            closeAll();
        }
        return list;
    }

    // 根据学号和课程编号查询成绩信息
    public Score findByXhaoAndKcbma(int xhao, String kcbma) {
        Score score = null;
        try {
            conn = DBConnect.getConnection();
            String sql = "SELECT * FROM ScoreInfo WHERE xhao=? AND kcbma=?";
            pstmt = conn.prepareStatement(sql);
            pstmt.setInt(1, xhao);
            pstmt.setString(2, kcbma);
            rs = pstmt.executeQuery();
            if (rs.next()) {
                score = new Score();
                score.setXhao(rs.getInt("xhao"));
                score.setKcbma(rs.getString("kcbma"));
                score.setXqi(rs.getInt("xqi"));
                score.setCji(rs.getInt("cji"));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            closeAll();
        }
        return score;
    }

    // 添加成绩信息
    public boolean add(Score score) {
        boolean flag = false;
        try {
            conn = DBConnect.getConnection();
            String sql = "INSERT INTO ScoreInfo(xhao,kcbma,xqi,cji) VALUES(?,?,?,?)";
            pstmt = conn.prepareStatement(sql);
            pstmt.setInt(1, score.getXhao());
            pstmt.setString(2, score.getKcbma());
            pstmt.setInt(3, score.getXqi());
            pstmt.setInt(4, score.getCji());
            int count = pstmt.executeUpdate();
            if (count > 0) {
                flag = true;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            closeAll();
        }
        return flag;
    }

    // 修改成绩信息
    public boolean update(Score score) {
        boolean flag = false;
        try {
            conn = DBConnect.getConnection();
            String sql = "UPDATE ScoreInfo SET xqi=?,cji=? WHERE xhao=? AND kcbma=?";
            pstmt = conn.prepareStatement(sql);
            pstmt.setInt(1, score.getXqi());
            pstmt.setInt(2, score.getCji());
            pstmt.setInt(3, score.getXhao());
            pstmt.setString(4, score.getKcbma());
            int count = pstmt.executeUpdate();
            if (count > 0) {
                flag = true;
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            closeAll();
        }
        return flag;
    }

    //