Add room service with first function 'getRooms()'

src/app/room.service.spec.ts

+import { TestBed, inject } from '@angular/core/testing';
+
+import { RoomService } from './room.service';
+
+describe('RoomService', () => {
+  beforeEach(() => {
+    TestBed.configureTestingModule({
+      providers: [RoomService]
+    });
+  });
+
+  it('should be created', inject([RoomService], (service: RoomService) => {
+    expect(service).toBeTruthy();
+  }));
+});

src/app/room.service.ts

+import { Injectable } from '@angular/core';
+import { Room } from './room';
+import { HttpClient, HttpHeaders } from '@angular/common/http';
+import { Observable } from 'rxjs/Observable';
+
+const httpOptions = {
+  headers: new HttpHeaders({'Content-Type': 'application/json'})
+};
+
+@Injectable()
+export class RoomService {
+
+  private roomsUrl = 'api/rooms';
+
+  constructor(private http: HttpClient) {
+  }
+
+  getRooms(): Observable<Room[]> {
+    return this.http.get<Room[]>(this.roomsUrl);
+  }
+}