ок

src/main/java/ru/IP_LabWorks/IP/University/Service/GroupService.java

@@ -0,0 +1,4 @@
+package ru.IP_LabWorks.IP.University.Service;
+
+public class GroupService {
+}

src/main/java/ru/IP_LabWorks/IP/University/Service/StudentService.java

@@ -1,4 +1,65 @@
 package ru.IP_LabWorks.IP.University.Service;
 
+import jakarta.persistence.Entity;
+import jakarta.persistence.EntityManager;
+import jakarta.persistence.EntityNotFoundException;
+import jakarta.persistence.PersistenceContext;
+import org.springframework.transaction.annotation.Transactional;
+import org.springframework.stereotype.Service;
+import org.springframework.util.StringUtils;
+import ru.IP_LabWorks.IP.University.Model.Student;
+
+import java.util.List;
+
+@Service
 public class StudentService {
+    @PersistenceContext
+    private EntityManager em;
+
+    @Transactional
+    public Student addStudent(String name, Integer age){
+        if (!StringUtils.hasText(name) || !StringUtils.hasText(String.valueOf(age))) {
+            throw new IllegalArgumentException("Student name or age is null or empty");
+        }
+        final Student student = new Student(name, age);
+        em.persist(student);
+        return student;
+    }
+
+    @Transactional(readOnly  = true)
+    public Student findStudent(Long id) {
+        final Student student = em.find(Student.class, id);
+        if (student == null) {
+            throw new EntityNotFoundException(String.format("Student with id [%s] is not found", id));
+        }
+        return student;
+    }
+
+    @Transactional(readOnly = true)
+    public List<Student> findAllStudents() {
+        return em.createQuery("select s from Student s", Student.class).getResultList();
+    }
+
+    @Transactional
+    public Student updateStudent(Long id, String name, Integer age) {
+        if (!StringUtils.hasText(name) || !StringUtils.hasText(String.valueOf(age))) {
+            throw new IllegalArgumentException("Student name or age is null or empty");
+        }
+        final Student currentStudent = findStudent(id);
+        currentStudent.setName(name);
+        currentStudent.setAge(age);
+        return em.merge(currentStudent);
+    }
+
+    @Transactional
+    public Student deleteStudent(Long id) {
+        final Student currentStudent = findStudent(id);
+        em.remove(currentStudent);
+        return currentStudent;
+    }
+
+    @Transactional
+    public void deleteAllStudent() {
+        em.createQuery("delete from Student").executeUpdate();
+    }
 }