用java写前端，MySQL写数据库做一个系统，内容包括：（1）教职工基本信息管理：教职工基本信息的增加、修 改与删除; （2）教职工签到管理：教职工输入编号后，签到，系统 自动记录其签到的时间，并注明是否迟到。 （3）教职工签到情况的查询与统计：按不同的条件对 工签到情况进行查询与统计 。java的后端代码具体怎么实现？不需要写前端。

好的，以下是Java后端代码的实现：

1. 建立教职工基本信息表和签到记录表的实体类：

public class Employee {
    private int id;
    private String name;
    private String gender;
    private Date birthDate;
    private String phone;
    // 省略getters和setters
}

public class CheckInRecord {
    private int id;
    private int employeeId;
    private Date checkInTime;
    private boolean isLate;
    // 省略getters和setters
}

2. 建立DAO类，实现与数据库的交互：

public class EmployeeDao {
    private Connection conn;

    // 构造方法中初始化数据库连接
    public EmployeeDao() {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection("jdbc:mysql://localhost/employee", "root", "password");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    // 添加教职工基本信息到数据库中
    public void addEmployee(Employee employee) throws SQLException {
        PreparedStatement stmt = conn.prepareStatement("INSERT INTO employee(name, gender, birth_date, phone) VALUES (?, ?, ?, ?)");
        stmt.setString(1, employee.getName());
        stmt.setString(2, employee.getGender());
        stmt.setDate(3, new java.sql.Date(employee.getBirthDate().getTime()));
        stmt.setString(4, employee.getPhone());

        stmt.executeUpdate();
    }

    // 修改教职工基本信息
    public void updateEmployee(Employee employee) throws SQLException {
        PreparedStatement stmt = conn.prepareStatement("UPDATE employee SET name=?, gender=?, birth_date=?, phone=? WHERE id=?");
        stmt.setString(1, employee.getName());
        stmt.setString(2, employee.getGender());
        stmt.setDate(3, new java.sql.Date(employee.getBirthDate().getTime()));
        stmt.setString(4, employee.getPhone());
        stmt.setInt(5, employee.getId());

        stmt.executeUpdate();
    }

    // 删除教职工基本信息
    public void deleteEmployee(int id) throws SQLException {
        PreparedStatement stmt = conn.prepareStatement("DELETE FROM employee WHERE id=?");
        stmt.setInt(1, id);

        stmt.executeUpdate();
    }

    // 根据教职工编号查询基本信息
    public Employee getEmployeeById(int id) throws SQLException {
        PreparedStatement stmt = conn.prepareStatement("SELECT * FROM employee WHERE id=?");
        stmt.setInt(1, id);

        ResultSet rs = stmt.executeQuery();
        Employee employee = null;
        if (rs.next()) {
            employee = new Employee();
            employee.setId(rs.getInt("id"));
            employee.setName(rs.getString("name"));
            employee.setGender(rs.getString("gender"));
            employee.setBirthDate(rs.getDate("birth_date"));
            employee.setPhone(rs.getString("phone"));
        }

        return employee;
    }
}

public class CheckInRecordDao {
    private Connection conn;

    // 构造方法中初始化数据库连接
    public CheckInRecordDao() {
        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection("jdbc:mysql://localhost/employee", "root", "password");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    // 添加签到记录到数据库中
    public void addCheckInRecord(CheckInRecord checkInRecord) throws SQLException {
        PreparedStatement stmt = conn.prepareStatement("INSERT INTO check_in_record(employee_id, check_in_time, is_late) VALUES (?, ?, ?)");
        stmt.setInt(1, checkInRecord.getEmployeeId());
        stmt.setTimestamp(2, new Timestamp(checkInRecord.getCheckInTime().getTime()));
        stmt.setBoolean(3, checkInRecord.isLate());

        stmt.executeUpdate();
    }

    // 根据教职工编号查询签到记录
    public List<CheckInRecord> getCheckInRecordByEmployeeId(int employeeId) throws SQLException {
        PreparedStatement stmt = conn.prepareStatement("SELECT * FROM check_in_record WHERE employee_id=?");
        stmt.setInt(1, employeeId);

        ResultSet rs = stmt.executeQuery();
        List<CheckInRecord> checkInRecords = new ArrayList<CheckInRecord>();
        while (rs.next()) {
            CheckInRecord checkInRecord = new CheckInRecord();
            checkInRecord.setId(rs.getInt("id"));
            checkInRecord.setEmployeeId(rs.getInt("employee_id"));
            checkInRecord.setCheckInTime(rs.getTimestamp("check_in_time"));
            checkInRecord.setLate(rs.getBoolean("is_late"));

            checkInRecords.add(checkInRecord);
        }

        return checkInRecords;
    }

    // 根据时间段查询签到记录
    public List<CheckInRecord> getCheckInRecordByTimeRange(Date start, Date end) throws SQLException {
        PreparedStatement stmt = conn.prepareStatement("SELECT * FROM check_in_record WHERE check_in_time BETWEEN ? AND ?");
        stmt.setTimestamp(1, new Timestamp(start.getTime()));
        stmt.setTimestamp(2, new Timestamp(end.getTime()));

        ResultSet rs = stmt.executeQuery();
        List<CheckInRecord> checkInRecords = new ArrayList<CheckInRecord>();
        while (rs.next()) {
            CheckInRecord checkInRecord = new CheckInRecord();
            checkInRecord.setId(rs.getInt("id"));
            checkInRecord.setEmployeeId(rs.getInt("employee_id"));
            checkInRecord.setCheckInTime(rs.getTimestamp("check_in_time"));
            checkInRecord.setLate(rs.getBoolean("is_late"));

            checkInRecords.add(checkInRecord);
        }

        return checkInRecords;
    }
}

3. 实现签到功能：

public class CheckInService {
    private CheckInRecordDao checkInRecordDao;

    public CheckInService() {
        checkInRecordDao = new CheckInRecordDao();
    }

    // 教职工签到
    public void checkIn(int employeeId) throws SQLException {
        EmployeeDao employeeDao = new EmployeeDao();
        Employee employee = employeeDao.getEmployeeById(employeeId);
        if (employee == null) {
            throw new RuntimeException("教职工不存在");
        }

        CheckInRecord checkInRecord = new CheckInRecord();
        checkInRecord.setEmployeeId(employeeId);
        checkInRecord.setCheckInTime(new Date());
        checkInRecord.setLate(checkIfLate());

        checkInRecordDao.addCheckInRecord(checkInRecord);
    }

    // 判断教职工是否迟到
    private boolean checkIfLate() {
        // 实现判断逻辑
    }
}

4. 实现查询和统计功能：

public class CheckInRecordService {
    private CheckInRecordDao checkInRecordDao;

    public CheckInRecordService() {
        checkInRecordDao = new CheckInRecordDao();
    }

    // 根据教职工编号查询签到记录
    public List<CheckInRecord> getCheckInRecordByEmployeeId(int employeeId) throws SQLException {
        return checkInRecordDao.getCheckInRecordByEmployeeId(employeeId);
    }

    // 根据时间段查询签到记录
    public List<CheckInRecord> getCheckInRecordByTimeRange(Date start, Date end) throws SQLException {
        return checkInRecordDao.getCheckInRecordByTimeRange(start, end);
    }

    // 统计教职工迟到次数
    public int countLateByEmployeeId(int employeeId) throws SQLException {
        List<CheckInRecord> checkInRecords = checkInRecordDao.getCheckInRecordByEmployeeId(employeeId);
        int count = 0;
        for (CheckInRecord checkInRecord : checkInRecords) {
            if (checkInRecord.isLate()) {
                count++;
            }
        }

        return count;
    }

    // 统计所有教职工迟到次数
    public int countLateAll() throws SQLException {
        List<CheckInRecord> checkInRecords = checkInRecordDao.getCheckInRecordByTimeRange(new Date(0), new Date());
        int count = 0;
        for (CheckInRecord checkInRecord : checkInRecords) {
            if (checkInRecord.isLate()) {
                count++;
            }
        }

        return count;
    }
}

以上就是Java后端代码的实现。其中，DAO类实现了对数据库的增删改查操作，Service类实现了业务逻辑，如签到、查询和统计等。当然，这只是一个简单的示例，实际应用中还需要考虑更多的细节和安全性问题。