MVC/StudentController.java

package com.studentmanagement.controller;

import com.studentmanagement.model.Student;
import com.studentmanagement.model.StudentDAO;
import com.studentmanagement.exception.StudentNotFoundException;
import com.studentmanagement.exception.DuplicateStudentException;

import java.util.List;

/**
 * 学生控制器，负责处理学生相关的业务逻辑
 * MVC模式中的Controller部分，连接Model和View
 */
public class StudentController {
    private StudentDAO studentDAO;

    /**
     * 构造函数
     */
    public StudentController() {
        this.studentDAO = StudentDAO.getInstance();
    }

    /**
     * 获取所有学生
     * @return 学生列表
     */
    public List<Student> getAllStudents() {
        return studentDAO.getAllStudents();
    }

    /**
     * 根据ID获取学生
     * @param id 学生ID
     * @return 学生对象
     * @throws StudentNotFoundException 当学生不存在时抛出
     */
    public Student getStudentById(int id) throws StudentNotFoundException {
        Student student = studentDAO.getStudentById(id);
        if (student == null) {
            throw new StudentNotFoundException(id);
        }
        return student;
    }

    /**
     * 添加学生
     * @param student 要添加的学生
     * @throws DuplicateStudentException 当学生ID已存在时抛出
     */
    public void addStudent(Student student) throws DuplicateStudentException {
        boolean added = studentDAO.addStudent(student);
        if (!added) {
            throw new DuplicateStudentException(student.getId());
        }
    }

    /**
     * 更新学生信息
     * @param student 要更新的学生
     * @throws StudentNotFoundException 当学生不存在时抛出
     */
    public void updateStudent(Student student) throws StudentNotFoundException {
        boolean updated = studentDAO.updateStudent(student);
        if (!updated) {
            throw new StudentNotFoundException(student.getId());
        }
    }

    /**
     * 删除学生
     * @param id 学生ID
     * @throws StudentNotFoundException 当学生不存在时抛出
     */
    public void deleteStudent(int id) throws StudentNotFoundException {
        boolean deleted = studentDAO.deleteStudent(id);
        if (!deleted) {
            throw new StudentNotFoundException(id);
        }
    }

    /**
     * 根据课程查找学生
     * @param course 课程名称
     * @return 该课程的学生列表
     */
    public List<Student> getStudentsByCourse(String course) {
        return studentDAO.getStudentsByCourse(course);
    }

    /**
     * 获取成绩高于指定分数的学生
     * @param grade 最低分数
     * @return 成绩高于指定分数的学生列表
     */
    public List<Student> getStudentsByGradeAbove(double grade) {
        return studentDAO.getStudentsByGradeAbove(grade);
    }

    /**
     * 计算指定课程的平均成绩
     * @param course 课程名称
     * @return 平均成绩
     */
    public double calculateAverageGradeByCourse(String course) {
        List<Student> students = getStudentsByCourse(course);
        if (students.isEmpty()) {
            return 0;
        }
        return students.stream()
                .mapToDouble(Student::getGrade)
                .average()
                .orElse(0);
    }

    /**
     * 获取所有学生的平均年龄
     * @return 平均年龄
     */
    public double calculateAverageAge() {
        List<Student> students = getAllStudents();
        if (students.isEmpty()) {
            return 0;
        }
        return students.stream()
                .mapToDouble(Student::getAge)
                .average()
                .orElse(0);
    }
}