Membangun Aplikasi Web dengan Spring Boot dan Angular

1. Ikhtisar

Spring Boot dan Angular membentuk tandem kuat yang berfungsi sangat baik untuk mengembangkan aplikasi web dengan footprint minimal.

Dalam tutorial ini, kita akan menggunakan Spring Boot untuk mengimplementasikan backend RESTful, dan Angular untuk membuat frontend berbasis JavaScript.

2. Aplikasi Spring Boot

Fungsionalitas aplikasi web demo kami akan sangat sederhana. Ini hanya akan dipersempit untuk mengambil dan menampilkan Daftar entitas JPA dari database H2 dalam memori, dan mempertahankan yang baru melalui formulir HTML biasa.

2.1. Dependensi Maven

Berikut adalah dependensi proyek Spring Boot kami:

 org.springframework.boot spring-boot-starter-web   org.springframework.boot spring-boot-starter-data-jpa   com.h2database h2 runtime 

Perhatikan bahwa kami menyertakan spring-boot-starter-web karena kami akan menggunakannya untuk membuat layanan REST, dan spring-boot-starter-jpa untuk mengimplementasikan lapisan persistensi.

Versi database H2 juga dikelola oleh induk Spring Boot.

2.2. Kelas Entitas JPA

Untuk membuat prototipe dengan cepat lapisan domain aplikasi kita, mari kita tentukan kelas entitas JPA sederhana, yang akan bertanggung jawab untuk memodelkan pengguna:

@Entity public class User { @Id @GeneratedValue(strategy = GenerationType.AUTO) private long id; private final String name; private final String email; // standard constructors / setters / getters / toString } 

2.3. The UserRepository Antarmuka

Karena kita akan membutuhkan fungsionalitas CRUD dasar pada entitas Pengguna , kita juga harus menentukan antarmuka UserRepository :

@Repository public interface UserRepository extends CrudRepository{} 

2.4. Pengontrol REST

Sekarang, mari kita terapkan REST API. Dalam hal ini, ini hanya pengontrol REST sederhana.

@RestController @CrossOrigin(origins = "//localhost:4200") public class UserController { // standard constructors private final UserRepository userRepository; @GetMapping("/users") public List getUsers() { return (List) userRepository.findAll(); } @PostMapping("/users") void addUser(@RequestBody User user) { userRepository.save(user); } } 

Tidak ada yang secara inheren kompleks dalam definisi kelas UserController .

Tentu saja, satu-satunya detail implementasi yang perlu diperhatikan di sini adalah penggunaan anotasi @CrossOrigin . Sesuai namanya, anotasi memungkinkan Cross-Origin Resource Sharing (CORS) di server.

Langkah ini tidak selalu diperlukan. Karena kami menerapkan frontend Angular kami ke // localhost: 4200 dan Boot backend kami ke // localhost: 8080 , browser akan menolak permintaan dari satu ke yang lain.

Terkait metode pengontrol, getUser () mengambil semua entitas Pengguna dari database. Demikian pula, metode addUser () mempertahankan entitas baru dalam database, yang diteruskan di badan permintaan.

Untuk mempermudah, kami sengaja meninggalkan implementasi pengontrol yang memicu validasi Spring Boot sebelum mempertahankan entitas. Namun, dalam produksi, kami tidak bisa mempercayai input pengguna, jadi validasi sisi server harus menjadi fitur wajib.

2.5. Bootstrap Aplikasi Spring Boot

Terakhir, mari buat kelas bootstrap Spring Boot standar dan isi database dengan beberapa entitas Pengguna :

@SpringBootApplication public class Application { public static void main(String[] args) { SpringApplication.run(Application.class, args); } @Bean CommandLineRunner init(UserRepository userRepository) { return args -> { Stream.of("John", "Julie", "Jennifer", "Helen", "Rachel").forEach(name -> { User user = new User(name, name.toLowerCase() + "@domain.com"); userRepository.save(user); }); userRepository.findAll().forEach(System.out::println); }; } }

Sekarang, jalankan aplikasinya. Seperti yang diharapkan, kita akan melihat daftar entitas Pengguna yang dicetak ke konsol saat memulai:

User{id=1, name=John, [email protected]} User{id=2, name=Julie, [email protected]} User{id=3, name=Jennifer, [email protected]} User{id=4, name=Helen, [email protected]} User{id=5, name=Rachel, [email protected]}

3. Aplikasi Sudut

Dengan demo aplikasi Spring Boot kami aktif dan berjalan, sekarang mari buat aplikasi Angular sederhana, yang mampu menggunakan API pengontrol REST.

3.1. Instalasi CLI Angular

Kami akan menggunakan Angular CLI, utilitas baris perintah yang kuat, untuk membuat aplikasi Angular kami.

Angular CLI adalah alat yang sangat berharga karena memungkinkan kita membuat keseluruhan proyek Angular dari awal, menghasilkan komponen, layanan, kelas, dan antarmuka hanya dengan beberapa perintah .

Setelah kami menginstal npm (Node Package Manager), kami akan membuka konsol perintah dan mengetik perintah:

npm install -g @angular/[email protected]

Itu dia. Perintah di atas akan menginstal versi terbaru dari CLI Angular.

3.2. Project Scaffolding dengan Angular CLI

Faktanya, kami dapat membuat struktur aplikasi Angular kami dari awal. Tapi sejujurnya, ini adalah tugas yang rawan kesalahan dan memakan waktu yang harus kita hindari dalam semua kasus.

Sebagai gantinya, kami akan membiarkan Angular CLI melakukan kerja keras untuk kami. Jadi, mari kita buka konsol perintah, lalu arahkan ke folder tempat kita ingin aplikasi kita dibuat dan ketik perintah:

ng new angularclient

The baru perintah akan menghasilkan seluruh struktur aplikasi dalam angularclient direktori.

3.3. Titik Masuk Aplikasi Angular

Jika kita melihat ke dalam folder angularclient , kita akan melihat bahwa Angular CLI telah secara efektif membuat keseluruhan proyek untuk kita.

Angular's application files use TypeScript, a typed superset of JavaScript that compiles to plain JavaScript. However, the entry point of any Angular application is a plain old index.html file.

Let's edit this file, as follows:

    Spring Boot - Angular Application         

As we can see above, we included Bootstrap 4, so we can give our application UI components a more fancy look. Of course, it's possible to pick up another UI kit from the bunch available out there.

Please notice the custom tags inside the section. At first sight, they look rather weird, as is not a standard HTML 5 element.

Let's keep them right there, as is the root selector that Angular uses for rendering the application's root component.

3.4. The app.component.ts Root Component

To better understand how Angular binds an HTML template to a component, let's go to the src/app directory and edit the app.component.ts TypeScript file – the root component:

import { Component } from '@angular/core'; @Component({ selector: 'app-root', templateUrl: './app.component.html', styleUrls: ['./app.component.css'] }) export class AppComponent { title: string; constructor() { this.title = 'Spring Boot - Angular Application'; } }

For obvious reasons, we'll not dive deep into learning TypeScript. Even so, let's notice that the file defines an AppComponent class, which declares a field title of type string (lower-cased). Definitively, it's typed JavaScript.

Additionally, the constructor initializes the field with a string value, which is pretty similar to what we do in Java.

The most relevant part is the @Component metadata marker or decorator, which defines three elements:

  1. selector – the HTML selector used to bind the component to the HTML template file
  2. templateUrl – the HTML template file associated with the component
  3. styleUrls – one or more CSS files associated with the component

As expected, we can use the app.component.html and app.component.css files to define the HTML template and the CSS styles of the root component.

Finally, the selector element binds the whole component to the selector included in the index.html file.

3.5. The app.component.html File

Since the app.component.html file allows us to define the root component's HTML template — the AppComponent class — we'll use it for creating a basic navigation bar with two buttons.

If we click the first button, Angular will display a table containing the list of User entities stored in the database. Similarly, if we click the second one, it will render an HTML form, which we can use for adding new entities to the database:

{{ title }}

  • List Users
  • Add User

The bulk of the file is standard HTML, with a few caveats worth noting.

The first one is the {{ title }} expression. The double curly braces {{ variable-name }} is the placeholder that Angular uses for performing variable interpolation.

Let's keep in mind that the AppComponent class initialized the title field with the value Spring Boot – Angular Application. Thus, Angular will display the value of this field in the template. Likewise, changing the value in the constructor will be reflected in the template.

The second thing to note is the routerLink attribute.

Angular uses this attribute for routing requests through its routing module (more on this later). For now, it's sufficient to know that the module will dispatch a request to the /users path to a specific component and a request to /adduser to another component.

In each case, the HTML template associated with the matching component will be rendered within the placeholder.

3.6. The User Class

Since our Angular application will fetch from and persist User entities in the database, let's implement a simple domain model with TypeScript.

Let's open a terminal console and create a model directory:

ng generate class user

Angular CLI will generate an empty User class. Let's populate it with a few fields:

export class User { id: string; name: string; email: string; }

3.7. The UserService Service

With our client-side domain User class already set, let's now implement a service class that performs GET and POST requests to the //localhost:8080/users endpoint.

This will allow us to encapsulate access to the REST controller in a single class, which we can reuse throughout the entire application.

Let's open a console terminal, then create a service directory, and within that directory, issue the following command:

ng generate service user-service

Now, let's open the user.service.ts file that Angular CLI just created and refactor it:

import { Injectable } from '@angular/core'; import { HttpClient, HttpHeaders } from '@angular/common/http'; import { User } from '../model/user'; import { Observable } from 'rxjs/Observable'; @Injectable() export class UserService { private usersUrl: string; constructor(private http: HttpClient) { this.usersUrl = '//localhost:8080/users'; } public findAll(): Observable { return this.http.get(this.usersUrl); } public save(user: User) { return this.http.post(this.usersUrl, user); } }

We don't need a solid background on TypeScript to understand how the UserService class works. Simply put, it encapsulates within a reusable component all the functionality required to consume the REST controller API that we implemented before in Spring Boot.

The findAll() method performs a GET HTTP request to the //localhost:8080/users endpoint via Angular's HttpClient. The method returns an Observable instance that holds an array of User objects.

Likewise, the save() method performs a POST HTTP request to the //localhost:8080/users endpoint.

By specifying the type User in the HttpClient‘s request methods, we can consume back-end responses in an easier and more effective way.

Lastly, let's notice the use of the @Injectable() metadata marker. This signals that the service should be created and injected via Angular's dependency injectors.

3.8. The UserListComponent Component

In this case, the UserService class is the thin middle-tier between the REST service and the application's presentation layer. Therefore, we need to define a component responsible for rendering the list of User entities persisted in the database.

Let's open a terminal console, then create a user-list directory and generate a user list component:

ng generate component user-list

Angular CLI will generate an empty component class that implements the ngOnInit interface. The interface declares a hook ngOnInit() method, which Angular calls after it has finished instantiating the implementing class, and after calling its constructor, too.

Let's refactor the class so that it can take a UserService instance in the constructor:

import { Component, OnInit } from '@angular/core'; import { User } from '../model/user'; import { UserService } from '../service/user.service'; @Component({ selector: 'app-user-list', templateUrl: './user-list.component.html', styleUrls: ['./user-list.component.css'] }) export class UserListComponent implements OnInit { users: User[]; constructor(private userService: UserService) { } ngOnInit() { this.userService.findAll().subscribe(data => { this.users = data; }); } } 

The implementation of the UserListComponent class is pretty self-explanatory. It simply uses the UserService's findAll() method to fetch all the entities persisted in the database and stores them in the users field.

Additionally, we need to edit the component's HTML file, user-list.component.html, to create the table that displays the list of entities:


    
# Name Email
{{ user.id }} {{ user.name }} {{ user.email }}

Notice the use of the *ngFor directive. The directive is called a repeater, and we can use it for iterating over the contents of a variable and iteratively rendering HTML elements. In this case, we used it for dynamically rendering the table's rows.

In addition, we used variable interpolation for showing the id,name, and email of each user.

3.9. The UserFormComponent Component

Similarly, we need to create a component that allows us to persist a new User object in the database.

Let's create a user-form directory and type the following:

ng generate component user-form 

Next, let's open the user-form.component.ts file and add to the UserFormComponent class a method for saving a User object:

import { Component } from '@angular/core'; import { ActivatedRoute, Router } from '@angular/router'; import { UserService } from '../service/user.service'; import { User } from '../model/user'; @Component({ selector: 'app-user-form', templateUrl: './user-form.component.html', styleUrls: ['./user-form.component.css'] }) export class UserFormComponent { user: User; constructor( private route: ActivatedRoute, private router: Router, private userService: UserService) { this.user = new User(); } onSubmit() { this.userService.save(this.user).subscribe(result => this.gotoUserList()); } gotoUserList() { this.router.navigate(['/users']); } }

In this case, UserFormComponent also takes a UserService instance in the constructor, which the onSubmit() method uses for saving the supplied User object.

Since we need to redisplay the updated list of entities once we have persisted a new one, we call the gotoUserList() method after the insertion, which redirects the user to the /users path.

In addition, we need to edit the user-form.component.html file and create the HTML form for persisting a new user in the database:

 Name Name is required Email Email is required Submit 

At a glance, the form looks pretty standard. But it encapsulates a lot of Angular's functionality behind the scenes.

Let's notice the use of the ngSubmit directive, which calls the onSubmit() method when the form is submitted.

Next, we have defined the template variable #userForm, so Angular adds automatically an NgForm directive, which allows us to keep track of the form as a whole.

The NgForm directive holds the controls that we created for the form elements with an ngModel directive and a name attribute and also monitors their properties, including their state.

The ngModel directive gives us two-way data binding functionality between the form controls and the client-side domain model – the User class.

This means that data entered in the form input fields will flow to the model – and the other way around. Changes in both elements will be reflected immediately via DOM manipulation.

Additionally, ngModel allows us to keep track of the state of each form control and perform client-side validation, by adding to each control different CSS classes and DOM properties.

In the above HTML file, we used the properties applied to the form controls only to display an alert box when the values in the form have been changed.

3.10. The app-routing.module.ts File

Although the components are functional in isolation, we still need to use a mechanism for calling them when the user clicks the buttons in the navigation bar.

This is where the RouterModule comes into play. So, let's open the app-routing.module.ts file, and configure the module, so it can dispatch requests to the matching components:

import { NgModule } from '@angular/core'; import { Routes, RouterModule } from '@angular/router'; import { UserListComponent } from './user-list/user-list.component'; import { UserFormComponent } from './user-form/user-form.component'; const routes: Routes = [ { path: 'users', component: UserListComponent }, { path: 'adduser', component: UserFormComponent } ]; @NgModule({ imports: [RouterModule.forRoot(routes)], exports: [RouterModule] }) export class AppRoutingModule { } 

As we can see above, the Routes array instructs the router which component to display when a user clicks a link or specifies a URL into the browser address bar.

A route is composed of two parts:

  1. Path – a string that matches the URL in the browser address bar
  2. Component – the component to create when the route is active (navigated)

If the user clicks the List Users button, which links to the /users path, or enters the URL in the browser address bar, the router will render the UserListComponent component's template file in the placeholder.

Likewise, if they click the Add User button, it will render the UserFormComponent component.

3.11. The app.module.ts File

Next, we need to edit the app.module.ts file, so Angular can import all the required modules, components, and services.

Additionally, we need to specify which provider we'll use for creating and injecting the UserService class. Otherwise, Angular won't be able to inject it into the component classes:

import { BrowserModule } from '@angular/platform-browser'; import { NgModule } from '@angular/core'; import { AppRoutingModule } from './app-routing.module'; import { FormsModule } from '@angular/forms'; import { HttpClientModule } from '@angular/common/http'; import { AppComponent } from './app.component'; import { UserListComponent } from './user-list/user-list.component'; import { UserFormComponent } from './user-form/user-form.component'; import { UserService } from './service/user.service'; @NgModule({ declarations: [ AppComponent, UserListComponent, UserFormComponent ], imports: [ BrowserModule, AppRoutingModule, HttpClientModule, FormsModule ], providers: [UserService], bootstrap: [AppComponent] }) export class AppModule { }

4. Running the Application

Finally, we're ready to run our application.

To accomplish this, let's first run the Spring Boot application, so the REST service is alive and listening for requests.

Setelah aplikasi Spring Boot dijalankan, buka konsol perintah dan ketik perintah berikut:

ng serve --open

Ini akan memulai server pengembangan langsung Angular dan juga membuka browser di // localhost: 4200 .

Kita harus melihat bilah navigasi dengan tombol untuk membuat daftar entitas yang ada dan untuk menambahkan yang baru. Jika kita mengklik tombol pertama, kita akan melihat di bawah bilah navigasi tabel dengan daftar entitas yang ada di database:

Demikian pula, mengklik tombol kedua akan menampilkan formulir HTML untuk mempertahankan entitas baru:

5. Kesimpulan

Dalam tutorial ini, kita belajar bagaimana membuat aplikasi web dasar dengan Spring Boot dan Angular .

Seperti biasa, semua contoh kode yang ditampilkan dalam tutorial ini tersedia di GitHub.