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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.

Further reading:

Interface Driven Controllers in Spring

Learn how to create controllers using Spring MVC request annotation on Java interfaces.

Spring REST API + OAuth2 + Angular

Learn how to set up OAuth2 for a Spring REST API using Spring Security 5 and how to consume that from an Angular client.

2. The Spring Boot Application

Our demo web application's functionality will be pretty simplistic indeed. It'll be 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>
    <scope>runtime</scope>
</dependency>

Note 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.

The H2 database version is also managed by the Spring Boot parent.

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 modelling 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 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, but since we're 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 the controller implementation triggering Spring Boot validation before persisting an entity. In production, however, we can't trust user input alone, 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 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. The Angular Application

With our demo Spring Boot application up and running, we can 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 we've installed npm (Node Package Manager), we'll open a command console and type the command:

npm install -g @angular/[email protected]

That's it. The above command will install the latest version of Angular CLI.

3.2. Project Scaffolding With Angular CLI

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 we can 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:

<!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 glance, they look rather weird, as <app-root> is not a standard HTML 5 element.

We'll keep them 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 won't dive deep into learning TypeScript. Even so, let's note 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 <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, so 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, we can 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 note 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 also after calling its constructor.

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.

In addition, 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>

We should note 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 re-display 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 note the use of the ngSubmit directive, which calls the onSubmit() method when the form is submitted.

Next we defined the template variable #userForm, so Angular automatically adds 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. It 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 different CSS classes and DOM properties to each control.

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. 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 <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, we'll first run the Spring Boot application, so the REST service is alive and listening for requests.

Once the Spring Boot application has been started, we'll 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 article, we learned how to build a basic web application with Spring Boot and Angular.

As usual, all the code samples shown in this article are available over on GitHub.

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Get started with Spring 5 and Spring Boot 2, through the Learn Spring course:

>> CHECK OUT THE COURSE
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