core.module.ts
import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { HttpClientModule } from '@angular/common/http';
​
import { SharedModule } from '../shared/shared.module';
import { UserService } from './user.service';
​
@NgModule({
  imports: [
    CommonModule,
    HttpClientModule,
    SharedModule
  ],
  declarations: [],
  providers: [UserService]
})
export class CoreModule {}

user.service.ts
import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable } from 'rxjs';
​
@Injectable({providedIn: 'root'})
export class UserService {
​
  constructor(private http: HttpClient) { }
​
  test() {
    let data: Observable<Object> = this.http.get('users/1');
​
    data.subscribe(result => console.log(result));
  }
}

users.component.ts
import { Component, OnInit } from '@angular/core';
import { Observable } from 'rxjs';
​
import { UserService } from '../core/user.service';
import { User } from '../core/user.model';
import { HttpErrorResponse } from '@angular/common/http';
​
@Component({
  selector: 'app-users',
  templateUrl: './users.component.html',
  styleUrls: ['./users.component.css']
})
export class UsersComponent implements OnInit {
  users: User[];
​
  constructor(private userService: UserService) {}
​
  ngOnInit() {
    this.userService
      .getUsers()
      .subscribe(
        (users: User[]) => this.users = users,
        (error: HttpErrorResponse) => console.log(error)
      );
  }
}

user.service.ts
import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable } from 'rxjs';
import { User } from './user.model';
​
@Injectable({
  providedIn: 'root'
})
export class UserService {
  constructor(private http: HttpClient) {}
​
  getUser(id: number): Observable<User> {
    return this.http.get<User>(`/users/${id}`);
  }
​
  getUsers(): Observable<User[]> {
    return this.http.get<User[]>('/users');
  }
​
  createUser(user: User): Observable<User> {
    return this.http.post<User>('/users', user);
  }
​
  updateUser(user: User): Observable<User> {
    return this.http.put<User>(`/users/${user.id}`, user);
  }
​
  deleteUser(user: User): Observable<User> {
    return this.http.delete<User>(`/users/${user.id}`);
  }
}