1. Overview
Spring Boot and Angular form a powerful tandem that works great for developing web applications with a minimal footprint.
In this tutorial, we’ll use Spring Boot for implementing a RESTful backend, and Angular for creating a JavaScript-based frontend.
2. The Spring Boot Application
Our demo web application’s functionality will be pretty simplistic indeed. It will be just narrowed to fetching and displaying a List of JPA entities from an in-memory H2 database, and persisting new ones through a plain HTML form.
2.1. The Maven Dependencies
Here are our Spring Boot project’s dependencies:
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>com.h2database</groupId>
<artifactId>h2</artifactId>
<version>1.4.197</version>
<scope>runtime</scope>
</dependency>
Notice that we included spring-boot-starter-web because we’ll use it for creating the REST service, and spring-boot-starter-jpa for implementing the persistence layer. Also, let’s make sure to check the latest version of the H2 database on Maven Central.
2.2. The JPA Entity Class
To quickly prototype our application’s domain layer, let’s define a simple JPA entity class, which will be responsible for modeling users:
@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 Interface
Since we’ll need basic CRUD functionality on the User entities, we must also define a UserRepository interface:
@Repository
public interface UserRepository extends CrudRepository<User, Long>{}
2.4. The REST Controller
Now, let’s implement the REST API. In this case, it’s just a simple REST controller.
@RestController
@CrossOrigin(origins = "http://localhost:4200")
public class UserController {
// standard constructors
private final UserRepository userRepository;
@GetMapping("/users")
public List<User> getUsers() {
return (List<User>) userRepository.findAll();
}
@PostMapping("/users")
void addUser(@RequestBody User user) {
userRepository.save(user);
}
}
There’s nothing inherently complex in the definition of the UserController class.
Of course, the only implementation detail worth noting here is the use of the @CrossOrigin annotation. As the name implies, the annotation enables Cross-Origin Resource Sharing (CORS) on the server.
This step isn’t always necessary. Since we are deploying our Angular frontend to http://localhost:4200 and our Boot backend to http://localhost:8080, the browser would otherwise deny requests from one to the other.
Regarding the controller methods, getUser() fetches all the User entities from the database. Similarly, the addUser() method persists a new entity in the database, which is passed in the request body.
To keep things simple, we deliberately left out of the controller implementation triggering Spring Boot validation before persisting an entity. In production, however, we just can’t trust user input, so server-side validation should be a mandatory feature.
2.5. Bootstrapping the Spring Boot Application
Finally, let’s create a standard Spring Boot bootstrapping class and populate the database with a few User entities:
@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);
};
}
}
Now, let’s run the application. As expected, we should see a list of User entities printed out to the console on startup:
User{id=1, name=John, email=john@domain.com}
User{id=2, name=Julie, email=julie@domain.com}
User{id=3, name=Jennifer, email=jennifer@domain.com}
User{id=4, name=Helen, email=helen@domain.com}
User{id=5, name=Rachel, email=rachel@domain.com}
3. The Angular Application
With our demo Spring Boot application up and running, let’s now create a simple Angular application, capable of consuming the REST controller API.
3.1. Angular CLI Installation
We’ll use Angular CLI, a powerful command-line utility, to create our Angular application.
Angular CLI is an extremely valuable tool since it allows us to create an entire Angular project from scratch, generating components, services, classes, and interfaces with just a few commands.
Once that we’ve installed npm (Node Package Manager), we’ll open a command console and type the command:
npm install -g @angular/cli@1.7.4
That’s it. The above command will install the latest version of Angular CLI.
3.2. Project Scaffolding with Angular CLI
As a matter of fact, we can generate our Angular application structure from the ground up. But honestly, this is an error-prone and time-consuming task that we should avoid in all cases.
Instead, we’ll let Angular CLI do the hard work for us. So, let’s open a command console, then navigate to the folder where we want our application to be created and type the command:
ng new angularclient
The new command will generate the entire application structure within the angularclient directory.
3.3. The Angular Application’s Entry Point
If we look inside the angularclient folder, we’ll see that Angular CLI has effectively created an entire project for us.
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:
<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Spring Boot - Angular Application</title>
<base href="/">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="icon" type="image/x-icon" href="favicon.ico">
<link rel="stylesheet"
href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css"
integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm"
crossorigin="anonymous">
</head>
<body>
<app-root></app-root>
</body>
</html>
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 <app-root></app-root> tags inside the <body> section. At first sight, they look rather weird, as <app-root> is not a standard HTML 5 element.
Let’s keep them right there, as <app-root> 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:
- selector – the HTML selector used to bind the component to the HTML template file
- templateUrl – the HTML template file associated with the component
- 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 <app-root> 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:
<div class="container">
<div class="row">
<div class="col-md-12">
<div class="card bg-dark my-5">
<div class="card-body">
<h2 class="card-title text-center text-white py-3">{{ title }}</h2>
<ul class="text-center list-inline py-3">
<li class="list-inline-item"><a routerLink="/users" class="btn btn-info">List Users</a></li>
<li class="list-inline-item"><a routerLink="/adduser" class="btn btn-info">Add User</a></li>
</ul>
</div>
</div>
<router-outlet></router-outlet>
</div>
</div>
</div>
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 <router-outlet></router-outlet> 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 http://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 = 'http://localhost:8080/users';
}
public findAll(): Observable<User[]> {
return this.http.get<User[]>(this.usersUrl);
}
public save(user: User) {
return this.http.post<User>(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 http://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 http://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:
<div class="card my-5">
<div class="card-body">
<table class="table table-bordered table-striped">
<thead class="thead-dark">
<tr>
<th scope="col">#</th>
<th scope="col">Name</th>
<th scope="col">Email</th>
</tr>
</thead>
<tbody>
<tr *ngFor="let user of users">
<td>{{ user.id }}</td>
<td>{{ user.name }}</td>
<td><a href="mailto:{{ user.email }}">{{ user.email }}</a></td>
</tr>
</tbody>
</table>
</div>
</div>
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:
<div class="card my-5">
<div class="card-body">
<form (ngSubmit)="onSubmit()" #userForm="ngForm">
<div class="form-group">
<label for="name">Name</label>
<input type="text" [(ngModel)]="user.name"
class="form-control" id="name" name="name" placeholder="Enter your name"
required #name="ngModel">
</div>
<div [hidden]="!name.pristine" class="alert alert-danger">Name is required</div>
<div class="form-group">
<label for="email">Email</label>
<input type="text" [(ngModel)]="user.email"
class="form-control" id="email" name="email" placeholder="Enter your email address"
required #email="ngModel">
<div [hidden]="!email.pristine" class="alert alert-danger">Email is required</div>
</div>
<button type="submit" [disabled]="!userForm.form.valid" class="btn btn-info">Submit</button>
</form>
</div>
</div>
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:
- Path – a string that matches the URL in the browser address bar
- 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 <router-outlet> 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.
Once the Spring Boot application has been started, let’s open a command console and type the following command:
ng serve --open
This will start Angular’s live development server and also open the browser at http://localhost:4200.
We should see the navigation bar with the buttons for listing existing entities and for adding new ones. If we click the first button, we should see below the navigation bar a table with the list of entities persisted in the database:
Similarly, clicking the second button will display the HTML form for persisting a new entity:
5. Conclusion
In this tutorial, we learned how to build a basic web application with Spring Boot and Angular.
As usual, all the code samples shown in this tutorial are available over on GitHub.