AbsenceManager/doc/day5.md

本次实验的主要任务是完成期末案例的**业务逻辑层**（Service Layer）开发。业务逻辑层是连接图形界面（GUI）和数据访问层（DAO）的桥梁，它包含了所有的业务规则和流程控制。

## 任务一：完成DAOFactory

在开始service层开发之前，我们需要先完成`DAOFactory`类。这个类使用了单例模式和工厂模式，用于统一管理和获取DAO层的实例。

```java
package dao;

import dao.impl.StudentDAOImpl;
import dao.impl.TeacherDAOImpl;
import dao.impl.LeaveRequestDAOImpl;

/**
 * DAO工厂类，用于获取各种DAO的实例
 */
public class DAOFactory {
    private static final StudentDAO studentDAO = new StudentDAOImpl();
    private static final TeacherDAO teacherDAO = new TeacherDAOImpl();
    private static final LeaveRequestDAO leaveRequestDAO = new LeaveRequestDAOImpl();

    /**
     * 私有构造函数，防止实例化
     */
    private DAOFactory() {
        // 私有构造函数，阻止实例化
    }

    /**
     * 获取StudentDAO实例
     * @return StudentDAO实例
     */
    public static StudentDAO getStudentDAO() {
        return studentDAO;
    }

    /**
     * 获取TeacherDAO实例
     * @return TeacherDAO实例
     */
    public static TeacherDAO getTeacherDAO() {
        return teacherDAO;
    }

    /**
     * 获取LeaveRequestDAO实例
     * @return LeaveRequestDAO实例
     */
    public static LeaveRequestDAO getLeaveRequestDAO() {
        return leaveRequestDAO;
    }
}
```

`DAOFactory`类的主要特点：
1. 使用私有构造函数防止外部实例化
2. 使用静态字段保存DAO实例，确保全局唯一
3. 提供静态方法获取DAO实例

后期你可以这样使用它来获取DAO实例：

```java
// 获取StudentDAO实例
StudentDAO studentDAO = DAOFactory.getStudentDAO();

// 获取TeacherDAO实例
TeacherDAO teacherDAO = DAOFactory.getTeacherDAO();

// 获取LeaveRequestDAO实例
LeaveRequestDAO leaveRequestDAO = DAOFactory.getLeaveRequestDAO();
```

## 任务二：开发Service层类

在`src/service`目录下创建以下服务类：

### 2.1 学生服务类（StudentService.java）

```java
package service;

import dao.DAOFactory;
import dao.StudentDAO;
import model.Student;

/**
 * 学生信息服务类
 */
public class StudentService {
    private final StudentDAO studentDAO = DAOFactory.getStudentDAO();

    /**
     * 根据ID查询学生
     * @param id 学生ID
     * @return 学生信息
     */
    public Student getStudentById(int id) {
        return studentDAO.findById(id);
    }

    /**
     * 学生登录
     * @param studentId 学号
     * @param password 密码
     * @return 登录成功返回学生信息，失败返回null
     */
    public Student login(String studentId, String password) {
        Student student = studentDAO.findByStudentId(studentId);
        if (student != null && password.equals(student.getPassword())) {
            return student;
        }
        return null;
    }
}
```

### 2.2 教师服务类（TeacherService.java）

```java
package service;

import dao.DAOFactory;
import dao.TeacherDAO;
import model.Teacher;

/**
 * 教师信息服务类
 */
public class TeacherService {
    private final TeacherDAO teacherDAO = DAOFactory.getTeacherDAO();

    /**
     * 教师登录
     * @param teacherId 教师工号
     * @param password 密码
     * @return 登录成功返回教师信息，失败返回null
     */
    public Teacher login(String teacherId, String password) {
        Teacher teacher = teacherDAO.findByTeacherId(teacherId);
        if (teacher != null && password.equals(teacher.getPassword())) {
            return teacher;
        }
        return null;
    }
}
```

### 2.3 请假服务类（LeaveRequestService.java）

[LeaveRequestService.java](https://static.seahi.me/2024/12/LeaveRequestService.java)

## 任务三：创建Service工厂类

为了方便获取Service实例，创建一个ServiceFactory类：

```java
package service;

/**
 * Service工厂类，用于获取各种Service的实例
 */
public class ServiceFactory {
    private static final StudentService studentService = new StudentService();
    private static final TeacherService teacherService = new TeacherService();
    private static final LeaveRequestService leaveRequestService = new LeaveRequestService();

    private ServiceFactory() {
        // 私有构造函数，防止实例化
    }

    public static StudentService getStudentService() {
        return studentService;
    }

    public static TeacherService getTeacherService() {
        return teacherService;
    }

    public static LeaveRequestService getLeaveRequestService() {
        return leaveRequestService;
    }
}
```

## 任务四：单元测试

在`test/service`目录下创建对应的测试类：

1. [StudentServiceTest.java](https://static.seahi.me/2024/12/StudentServiceTest.java) - 测试学生登录功能
2. [TeacherServiceTest.java](https://static.seahi.me/2024/12/TeacherServiceTest.java) - 测试教师登录功能
3. [LeaveRequestServiceTest.java](https://static.seahi.me/2024/12/LeaveRequestServiceTest.java) - 测试请假申请和审批功能