Service layer for Restful Web Service using CRUDService interface for CRUD operations.

CRUDService.java

package com.bytestree.restful.service;

import java.io.Serializable;
import java.util.List;

public interface CRUDService<E> {

	E save(E entity);

	E getById(Serializable id);

	List<E> getAll();

	void delete(Serializable id);
}

DefaultEmployeeService.java

package com.bytestree.restful.service;

import java.io.Serializable;
import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import com.bytestree.restful.model.Employee;
import com.bytestree.restful.repository.EmployeeRepository;

@Service
public class DefaultEmployeeService implements EmployeeService {

	@Autowired
	private EmployeeRepository employeeRepository;

	@Override
	public Employee save(Employee entity) {
		return employeeRepository.save(entity);
	}

	@Override
	public Employee getById(Serializable id) {
		return employeeRepository.findOne((Long) id);
	}

	@Override
	public List<Employee> getAll() {
		return employeeRepository.findAll();
	}

	@Override
	public void delete(Serializable id) {
		employeeRepository.delete((Long) id);
	}

}

EmployeeService.java

package com.bytestree.restful.service;

import com.bytestree.restful.model.Employee;

public interface EmployeeService extends CRUDService<Employee> {

}

For complete example refer RESTful Web Service CRUD Operations with Spring Boot