# Create a simple REST API

package com.example.restdemo.employee;

public class Employee {
    private String id;
    private String name;
    private String department;
    private int age;

    public Employee(String id, String name, String department, int age) {
        this.id = id;
        this.name = name;
        this.department = department;
        this.age = age;
    }

    public String getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    public String getDepartment() {
        return department;
    }

    public void setDepartment(String department) {
        this.department = department;
    }

    public int getAge() {
        return age;
    }

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

package com.example.restdemo.employee;

import org.springframework.stereotype.Service;

import java.util.ArrayList;
import java.util.HashMap;

@Service
public class EmployeeService {

    private HashMap<String, Employee> employees = new HashMap<>();

    public void addEmployee(Employee Emp) {
       this.employees.put(Emp.getId(), Emp);
    }

    public void removeEmployee(String empId) {
        this.employees.remove(empId);
    }

    public int countEmployees() {
        return this.employees.size();
    }

    public ArrayList<Employee> getEmployees() {

        ArrayList<Employee> empList = new ArrayList<>();
        // go through the values of the map
        for (Employee emp : employees.values()) {
            empList.add(emp);
        }

        return empList;
    }

}

package com.example.restdemo.employee;

import com.google.gson.Gson;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

import java.util.ArrayList;

@RestController
public class EmployeeController {

    @Autowired
    EmployeeService employeeService;

    @GetMapping("/employee/all")
    String getAllEmployees() {
        ArrayList<Employee> allEmployees = employeeService.getEmployees();
        String json = new Gson().toJson(allEmployees);
        return json;
    }

    @PutMapping(value="/employee/add", consumes = "application/json")
    int addEmployee(@RequestBody Employee newEmployee) {

        employeeService.addEmployee(newEmployee);
        int newCount = employeeService.countEmployees();
        return newCount;
    }

    @DeleteMapping(value="/employee/delete", consumes = "application/json")
    int deleteEmployee(@RequestBody String empId) {

        employeeService.removeEmployee(empId);
        int newCount = employeeService.countEmployees();
        return newCount;
    }

}

<!-- https://mvnrepository.com/artifact/com.google.code.gson/gson -->
<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.10.1</version>
</dependency>

java -jar target/rest-demo-v1.jar
.   ____          _            __ _ _
/\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/  ___)| |_)| | | | | || (_| |  ) ) ) )
'  |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot ::                (v3.0.1)

2023-01-07T20:57:50.440+02:00  INFO 2440 --- [           main] c.example.restdemo.RestDemoApplication   : Starting RestDemoApplication vv1 using Java 19.0.1 with PID 2440 (D:\GitHub-Projects\Projects\Spring-Boot\APIs\SimpleAPI\rest-demo\target\rest-demo-v1.jar started by Catalin in D:\GitHub-Projects\Projects\Spring-Boot\APIs\SimpleAPI\rest-demo)
2023-01-07T20:57:50.443+02:00  INFO 2440 --- [           main] c.example.restdemo.RestDemoApplication   : No active profile set, falling back to 1 default profile: "default"
2023-01-07T20:57:51.232+02:00  INFO 2440 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2023-01-07T20:57:51.241+02:00  INFO 2440 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2023-01-07T20:57:51.241+02:00  INFO 2440 --- [           main] o.apache.catalina.core.StandardEngine    : Starting Servlet engine: [Apache Tomcat/10.1.4]
2023-01-07T20:57:51.311+02:00  INFO 2440 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2023-01-07T20:57:51.312+02:00  INFO 2440 --- [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 820 ms
2023-01-07T20:57:51.656+02:00  INFO 2440 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2023-01-07T20:57:51.671+02:00  INFO 2440 --- [           main] c.example.restdemo.RestDemoApplication   : Started RestDemoApplication in 1.576 seconds (process running for 1.925)