Spring MVC CRUD with Example

import lombok.*;
import javax.persistence.*;

@NoArgsConstructor
@AllArgsConstructor
@Data
@Entity
@Table(name = "courses")
public class Course {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "course_name")
    private String courseName;

    @Column(name = "instructor")
    private String instructor;

    @Column(name = "email")
    private String email;
}

import com.example.testing_001.model.Course;
import org.springframework.data.jpa.repository.JpaRepository;

@Repository
public interface CourseRepository extends JpaRepository<Course, Long> {

}

import com.example.testing_001.model.Course;
import java.util.List;
import org.springframework.data.domain.Page;

public interface CourseService {
    List<Course> getAllCourses();
    void saveCourse(Course course);
    Course getCourseById(long id);
    void deleteCourseById(long id);
    Page<Course> findPaginated(int pageNum, int pageSize,
                               String sortField,
                               String sortDirection);
}

import com.example.testing_001.model.Course;
import com.example.testing_001.repository.CourseRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageRequest;
import org.springframework.data.domain.Pageable;
import org.springframework.data.domain.Sort;
import org.springframework.stereotype.Service;

import java.util.List;
import java.util.Optional;

@Service
public class CourseServiceImpl implements CourseService{

    @Autowired
    private CourseRepository courseRepository;

    @Override
    public List<Course> getAllCourses() {
        return courseRepository.findAll();
    }

    @Override
    public void saveCourse(Course course) {
        this.courseRepository.save(course);
    }

    @Override
    public Course getCourseById(long id) {
        Optional<Course> optionalCourse = courseRepository.findById(id);
        Course course = null;
        if (optionalCourse.isPresent()) {
            course = optionalCourse.get();
        } else {
            throw new RuntimeException("Course not found for id : " + id);
        }
        return course;
    }

    @Override
    public void deleteCourseById(long id) {
        this.courseRepository.deleteById(id);
    }

    @Override
    public Page<Course> findPaginated(int pageNum, int pageSize, String sortField, String sortDirection) {
        Sort sort = sortDirection.equalsIgnoreCase(Sort.Direction.ASC.name()) ? Sort.by(sortField).ascending() :
                Sort.by(sortField).descending();

        Pageable pageable = PageRequest.of(pageNum - 1, pageSize, sort);
        return this.courseRepository.findAll(pageable);
    }
}

import com.example.testing_001.model.Course;
import com.example.testing_001.service.CourseService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Page;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.*;

import java.util.List;

@Controller
public class CourseController {

    @Autowired
    private CourseService courseService;

    @GetMapping("/")
    public String viewHomePage(Model model) {
        return findPaginated(1, "courseName", "asc", model);
    }

    @GetMapping("/add")
    public String showNewCourseForm(Model model) {
        Course Course = new Course();
        model.addAttribute("course", Course);
        return "new_course";
    }

    @PostMapping("/save")
    public String saveCourse(@ModelAttribute("course") Course course) {
        // save Course to database
        courseService.saveCourse(course);
        return "redirect:/";
    }

    @GetMapping("/update/{id}")
    public String showFormForUpdate(@PathVariable( value = "id") long id, Model model) {

        Course course = courseService.getCourseById(id);
        model.addAttribute("course", course);
        return "update_course";
    }

    @GetMapping("/delete/{id}")
    public String deleteCourse(@PathVariable (value = "id") long id) {

        this.courseService.deleteCourseById(id);
        return "redirect:/";
    }


    @GetMapping("/page/{pageNo}")
    public String findPaginated(@PathVariable (value = "pageNo") int pageNo,
                                @RequestParam("sortField") String sortField,
                                @RequestParam("sortDir") String sortDir,
                                Model model) {
        int pageSize = 5;

        Page<Course> page = courseService.findPaginated(pageNo, pageSize, sortField, sortDir);
        List<Course> listCourses = page.getContent();

        model.addAttribute("currentPage", pageNo);
        model.addAttribute("totalPages", page.getTotalPages());
        model.addAttribute("totalItems", page.getTotalElements());

        model.addAttribute("sortField", sortField);
        model.addAttribute("sortDir", sortDir);
        model.addAttribute("reverseSortDir", sortDir.equals("asc") ? "desc" : "asc");

        model.addAttribute("listCourses", listCourses);
        return "index";
    }
}