ADD file via upload

StudentController.java

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+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);
+    }
+}