Spring Boot - Difference Between @Service Annotation and @Repository Annotation

// Java Program to Illustrate MyServiceClass

// Importing package module to code module
package com.example.demo.service;
// Importing required classes
import org.springframework.stereotype.Service;

// Annotation
@Service

// Class
public class MyServiceClass {

    // Method
    // To compute factorial
    public int factorial(int n)
    {
        // Base case
        if (n == 0)
            return 1;

        return n * factorial(n - 1);
    }
}

// Java Program to Illustrate DemoApplication

// Importing package module to code fragment
package com.example.demo;
// Importing required classes
import com.example.demo.service.MyServiceClass;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

// Annotation
@SpringBootApplication

// Main class
public class DemoApplication {

    // MAin driver method
    public static void main(String[] args)
    {

        AnnotationConfigApplicationContext context
            = new AnnotationConfigApplicationContext();
        context.scan("com.example.demo");

        context.refresh();

        MyServiceClass myServiceClass
            = context.getBean(MyServiceClass.class);

        // Testing the factorial method
        int factorialOf5 = myServiceClass.factorial(5);
        System.out.println("Factorial of 5 is: "
                           + factorialOf5);

        // Closing the spring context
        // using close() method
        context.close();
    }
}

// Java Program to Illustrate Simple POJO (Plain Old Java
// Object) Class

package com.example.demo.entity;

// Class
public class Student {

    // Attributes
    private Long id;
    private String name;
    private int age;

    // Generating the constructor
    public Student(Long id, String name, int age)
    {
        this.id = id;
        this.name = name;
        this.age = age;
    }

    // Getter-setters
    public Long getId() { return id; }

    public void setId(Long id) { this.id = id; }

    public String getName() { return name; }

    public void setName(String name) { this.name = name; }

    public int getAge() { return age; }

    public void setAge(int age) { this.age = age; }

    // Overriding toString() method of String class
    @Override public String toString()
    {
        return "Student{"
            + "id=" + id + ", name='" + name + '\''
            + ", age=" + age + '}';
    }
}

// Java Program to illustrate DemoRepository File

package com.example.demo.repository;

public interface DemoRepository<T> {

    // Save method
    public void save(T t);

    // Find a student by its id
    public T findStudentById(Long id);

}

// Java Program to Illustrate StudentRepository File

package com.example.demo.repository;

import com.example.demo.entity.Student;
import org.springframework.stereotype.Repository;

import java.util.HashMap;
import java.util.Map;

@Repository
public class StudentRepository implements DemoRepository<Student> {

    // Using an in-memory Map
    // to store the object data
    private Map<Long, Student> repository;

    public StudentRepository() {
        this.repository = new HashMap<>();
    }

    // Implementation for save method
    @Override
    public void save(Student student) {
        repository.put(student.getId(), student);
    }

    // Implementation for findStudentById method
    @Override
    public Student findStudentById(Long id) {
        return repository.get(id);
    }
}

// Java Program to Illustrate Spring Repository Test

package com.example.demo;

import com.example.demo.entity.Student;
import com.example.demo.repository.StudentRepository;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

// Class
@SpringBootApplication
public class DemoApplication {

    // Main driver method
    public static void main(String[] args)
    {

        AnnotationConfigApplicationContext context
            = new AnnotationConfigApplicationContext();
        context.scan("com.example.demo");
        context.refresh();

        StudentRepository repository
            = context.getBean(StudentRepository.class);

        // Testing the store method
        repository.save(new Student(1L, "Anshul", 25));
        repository.save(new Student(2L, "Mayank", 23));

        // Testing the retrieve method
        Student student = repository.findStudentById(1L);
        System.out.println(student);

        // Closing the spring context
        // using standard close() method
        context.close();
    }
}