from origin 'http://localhost:4200' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource

Question

My client-side application(Front end) - Angular My server-side application(Back end) - Java JAX-RS (jersy)

I'm getting this error when I call a function from frontend to backend

My angular service code

import { User } from './../model/user';
import { Injectable } from '@angular/core';
import { HttpClient, HttpHeaders } from '@angular/common/http';
import { Observable } from 'rxjs';

const headeroption = {
  headers: new HttpHeaders({ 'Content-Type': 'application/json' })
};

@Injectable({
  providedIn: 'root'
})
export class UserService {

  constructor(private http: HttpClient) { }

  url = 'http://localhost:9090/HealthCare2/services/';

  user: Observable<User[]>;

  //Testing
  test() {
    return this.http.get(this.url + 'user/test');
  }

My Java JAX-RS Controller

@Path("/user")
public class UserController {

    UserService userService = new UserService();

    // Test function
    @GET
    @Path("/test")
    @Produces(MediaType.TEXT_HTML)
    public String testing() {

        return "Test Function is working";

    }
}