I am sure that you have enjoyed the part1 where just a blink of an eye we set up an in-memory database, create a Repository class using Spring Data JPA and insert data using initDataloader by Spring boot.
In this tutorial, we will expose those employee data to UI, The Classic  MVC pattern using Spring boot.
The Service Part:: In my previous article I have created an EmployeeRepository interface & Spring boot provide its implementation at runtime, now I want this data to be guided to the Service Layer. To achieve that, I need to inject that Repository to Service layer, and define the CRUD methods which are doing nothing but calls the Repositories CRUD methods, Now you may be wondering, the EmployeeRepository interface  is empty and it extends CRUDRepository, where you can only find the declaration of CRUD methods, Now the question is, where are the Implementations ?
Again the Answer is Spring-boot on the runtime it creates an Implementation class which has all the CRUD methods implementations. Interesting isn’t it,  We just declare an interface and Container creates  all the stuff for us, and we save lots of our precious time, get rid of silly mistakes etc. really an IOC(Inversion of Control)
Let’s see How the Service part looks like, Please note for simplicity, I print the messages in the console using Sysout, But in the real project don’t ever do this, use Logger always.
package com.example.layerdArchitechture.service;
import java.util.Optional;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import com.example.layerdArchitechture.entity.Employee;
import com.example.layerdArchitechture.repository.EmployeeRepositiry;

@Service
public class EmployeeService {
@Autowired
EmployeeRepositiry repo;
public Employee addEmployee(Employee emp) {
emp = repo.save(emp);
System.out.println(“Employee saved::” + emp);
return emp;
}
public Optional<Employee> findEmployeeById(Long empId) {
Optional<Employee> emp = repo.findById(empId);
System.out.println(“Employee found::” + emp);
return emp;
}
public Iterable<Employee> findAllEmployee() {
return repo.findAll();
}
public void deleteEmployeeById(Employee emp) {
repo.delete(emp);
System.out.println(“Employee deleted::” + emp);
}
}
Yeah, Our service Layer is ready, Now I need a Controller part which will act as a delegator, takes data from UI send it to Service and Vice versa, I personally recommend to use Controller as a thin layer which just porting data from UI to service and service to UI and maybe doing some data format conversion stuffs nothing more than that.
Before showing you the code of the controller let me remind you I have not use a proper Spring controller which forward the response to a view rather, I use a RestController which directly deliver the response payload in JSON / XML format, based on the Produces property. by default it is JSON.
In Controller, we map the URL pattern to a controller method bind any data coming from a form into a  Model the “M “ part of MVC.
Let’s see the code.
package com.example.layerdArchitechture.controller;
import java.util.Optional;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import com.example.layerdArchitechture.entity.Employee;
import com.example.layerdArchitechture.service.EmployeeService;
@RestController
public class EmployeeController {
@Autowired
EmployeeService service;
@RequestMapping(“/TCS/employees”)
public Iterable<Employee> findAllEmployee() {
return service.findAllEmployee();
}
@RequestMapping(“/TCS/employee/{id}”)
public Employee findbyId(@PathVariable Long id) {
Optional<Employee> emplyoeeContainer = service.findEmployeeById(id);
return emplyoeeContainer.isPresent()?emplyoeeContainer.get():null;
}
@RequestMapping(“/TCS/employee/addDemoEmployee”)
public Employee addEmployee() {
Employee emp = new Employee();
emp.setName(“Demo Demo”);
emp.setSex(“M”);
emp.setAddress(“Demo”);
return service.addEmployee(emp);
}

@RequestMapping(“/TCS/employee/delete/{id}”)
public String delete(@PathVariable Long id) {
Optional<Employee> emp = service.findEmployeeById(id);
if(emp.isPresent()) {
 service.deleteEmployeeById(emp.get());
 return “deleted Successfully”;
}
return “Employee Not Exists, Not able to delete”;
}
}

If you look at the Controller class, You can see I autowired the Service class then wrote CRUD methods(also map them with Url pattern) as a wrapper which internally calls Service Wrapper method which calls the Spring boot’s Repository Implementation class.
Now If I run the spring boot application class and hit following URL in the browser
http://localhost:8080/TCS/employees
I can see the following response in Browser in JSON format.
[
  {
    “id”: 1,
    “name”: “Shamik Mitra”,
    “address”: “BagBazar”,
    “sex”: “M”
  },
  {
    “id”: 2,
    “name”: “Samir Mitra”,
    “address”: “BagBazar”,
    “sex”: “M”
  },
  {
    “id”: 3,
    “name”: “Swastika Basu”,
    “address”: “Baranagar”,
    “sex”: “F”
  }
]
Hope you enjoyed the post.

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