可以给我用java和数据库写一个请假系统吗

当然可以，以下是一个简单的请假管理系统的代码示例，使用 Java 编程语言和 MySQL 数据库：

1. 创建请假请求表：

CREATE TABLE leave_request (
  id INT NOT NULL AUTO_INCREMENT,
  employee_id INT NOT NULL,
  start_date DATE NOT NULL,
  end_date DATE NOT NULL,
  reason TEXT,
  status VARCHAR(20) NOT NULL,
  PRIMARY KEY (id)
);

2. 创建员工表：

CREATE TABLE employee (
  id INT NOT NULL AUTO_INCREMENT,
  name VARCHAR(50) NOT NULL,
  email VARCHAR(50) NOT NULL,
  password VARCHAR(50) NOT NULL,
  role VARCHAR(20) NOT NULL,
  PRIMARY KEY (id)
);

3. 创建 Java 类：

请假请求实体类：

public class LeaveRequest {
    private int id;
    private int employeeId;
    private Date startDate;
    private Date endDate;
    private String reason;
    private String status;
    // 省略 getter 和 setter 方法
}

员工实体类：

public class Employee {
    private int id;
    private String name;
    private String email;
    private String password;
    private String role;
    // 省略 getter 和 setter 方法
}

请假请求 DAO 类：

public class LeaveRequestDao {
    private Connection conn;
    // 构造函数
    public LeaveRequestDao(Connection conn) {
        this.conn = conn;
    }
    // 插入请假请求
    public void insert(LeaveRequest request) throws SQLException {
        String sql = "INSERT INTO leave_request (employee_id, start_date, end_date, reason, status) VALUES (?, ?, ?, ?, ?)";
        PreparedStatement stmt = conn.prepareStatement(sql);
        stmt.setInt(1, request.getEmployeeId());
        stmt.setDate(2, new java.sql.Date(request.getStartDate().getTime()));
        stmt.setDate(3, new java.sql.Date(request.getEndDate().getTime()));
        stmt.setString(4, request.getReason());
        stmt.setString(5, request.getStatus());
        stmt.executeUpdate();
    }
    // 查询所有请假请求
    public List<LeaveRequest> findAll() throws SQLException {
        List<LeaveRequest> requests = new ArrayList<LeaveRequest>();
        String sql = "SELECT * FROM leave_request";
        PreparedStatement stmt = conn.prepareStatement(sql);
        ResultSet rs = stmt.executeQuery();
        while (rs.next()) {
            LeaveRequest request = new LeaveRequest();
            request.setId(rs.getInt("id"));
            request.setEmployeeId(rs.getInt("employee_id"));
            request.setStartDate(rs.getDate("start_date"));
            request.setEndDate(rs.getDate("end_date"));
            request.setReason(rs.getString("reason"));
            request.setStatus(rs.getString("status"));
            requests.add(request);
        }
        return requests;
    }
    // 根据 ID 查询请假请求
    public LeaveRequest findById(int id) throws SQLException {
        String sql = "SELECT * FROM leave_request WHERE id=?";
        PreparedStatement stmt = conn.prepareStatement(sql);
        stmt.setInt(1, id);
        ResultSet rs = stmt.executeQuery();
        if (rs.next()) {
            LeaveRequest request = new LeaveRequest();
            request.setId(rs.getInt("id"));
            request.setEmployeeId(rs.getInt("employee_id"));
            request.setStartDate(rs.getDate("start_date"));
            request.setEndDate(rs.getDate("end_date"));
            request.setReason(rs.getString("reason"));
            request.setStatus(rs.getString("status"));
            return request;
        } else {
            return null;
        }
    }
}

员工 DAO 类：

public class EmployeeDao {
    private Connection conn;
    // 构造函数
    public EmployeeDao(Connection conn) {
        this.conn = conn;
    }
    // 根据用户名和密码查询员工
    public Employee findByEmailAndPassword(String email, String password) throws SQLException {
        String sql = "SELECT * FROM employee WHERE email=? AND password=?";
        PreparedStatement stmt = conn.prepareStatement(sql);
        stmt.setString(1, email);
        stmt.setString(2, password);
        ResultSet rs = stmt.executeQuery();
        if (rs.next()) {
            Employee employee = new Employee();
            employee.setId(rs.getInt("id"));
            employee.setName(rs.getString("name"));
            employee.setEmail(rs.getString("email"));
            employee.setPassword(rs.getString("password"));
            employee.setRole(rs.getString("role"));
            return employee;
        } else {
            return null;
        }
    }
}

4. 创建 Web 应用程序：

您可以使用 Java Web 框架，例如 Spring MVC 或 Struts2，来创建 Web 应用程序并实现请假管理系统的功能。例如，您可以创建以下页面：

- 登录页面：员工可以使用他们的邮箱和密码登录系统。
- 请假请求页面：员工可以提交新的请假请求。
- 请假审批页面：主管可以查看并批准或拒绝请假请求。
- 请假记录页面：HR 管理员可以查看所有请假请求的记录和统计数据。

以上是一个简单的请假管理系统的示例，您可以根据实际需求进行修改和扩展。