Изграждане на уеб приложение с Spring Boot и Angular

1. Общ преглед

Spring Boot и Angular образуват мощен тандем, който работи чудесно за разработване на уеб приложения с минимален отпечатък.

В този урок ще използваме Spring Boot за внедряване на RESTful бекенд и Angular за създаване на базиран на JavaScript интерфейс.

2. Приложението Spring Boot

Функционалността на нашето демо уеб приложение ще бъде наистина опростена. Той просто ще бъде стеснен до извличане и показване на Списък на JPA обекти от база данни в паметта H2 и запазване на нови чрез обикновен HTML формуляр.

2.1. Зависимостите на Maven

Ето зависимостите на проекта Spring Boot:

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

Забележете, че включихме spring-boot-starter-web, защото ще го използваме за създаване на REST услугата и spring-boot-starter-jpa за внедряване на персистиращия слой.

Версията на базата данни H2 също се управлява от родителя Spring Boot.

2.2. Класът на JPA Entity

За да прототипираме бързо прототипа на домейна на нашето приложение, нека дефинираме прост JPA клас на обект, който ще отговаря за моделирането на потребители:

@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. В UserRepository интерфейс

Тъй като ще се нуждаем от основна CRUD функционалност на потребителските обекти, трябва да дефинираме и интерфейс UserRepository :

@Repository public interface UserRepository extends CrudRepository{} 

2.4. Контролерът REST

Сега, нека приложим REST API. В този случай това е просто обикновен контролер REST.

@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); } } 

В дефиницията на класа UserController няма нищо сложно по своята същност .

Разбира се, единствената подробност за изпълнение, която си струва да се отбележи тук, е използването на анотацията @CrossOrigin . Както подсказва името, анотацията дава възможност за споделяне на ресурси с различни източници (CORS) на сървъра.

Тази стъпка не винаги е необходима. Тъй като ние разполагаме нашата Angular фронтална връзка към // localhost: 4200 и нашата Boot backend към // localhost: 8080 , браузърът иначе би отказал заявки от единия към другия.

По отношение на методите на контролера, getUser () извлича всички потребителски обекти от базата данни. По подобен начин методът addUser () продължава нов обект в базата данни, който се предава в тялото на заявката.

За да улесним нещата, умишлено оставихме извън изпълнението на контролера, задействайки валидирането на Spring Boot, преди да продължим да съществуваме обект. В производството обаче ние просто не можем да се доверим на въвеждането от потребителя, така че проверката от страна на сървъра трябва да бъде задължителна функция.

2.5. Стартиране на приложението Spring Boot

И накрая, нека създадем стандартен клас за зареждане на Spring Boot и да попълним базата данни с няколко потребителски обекта:

@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); }; } }

Сега, нека стартираме приложението. Както се очакваше, трябва да видим списък с потребителски обекти, отпечатани на конзолата при стартиране:

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. Ъгловото приложение

С нашето демонстрационно приложение Spring Boot, работещо, нека сега създадем просто Angular приложение, способно да консумира API на REST контролера.

3.1. Ъглова CLI инсталация

Ще използваме Angular CLI, мощна помощна програма за команден ред, за да създадем нашето приложение Angular.

Angular CLI е изключително ценен инструмент, тъй като ни позволява да създадем цял Angular проект от нулата, генерирайки компоненти, услуги, класове и интерфейси само с няколко команди .

След като инсталираме npm (Node Package Manager), ще отворим командна конзола и ще напишем командата:

npm install -g @angular/[email protected]

Това е. Горната команда ще инсталира най-новата версия на Angular CLI.

3.2. Проектно скеле с ъглова CLI

В интерес на истината, ние можем да генерираме нашата Angular структура на приложение от нулата. Но честно казано, това е склонна към грешки и отнемаща време задача, която трябва да избягваме във всички случаи.

Вместо това ще оставим Angular CLI да свърши тежката работа вместо нас. И така, нека отворим командна конзола, след това отидете до папката, в която искаме да бъде създадено нашето приложение и въведете командата:

ng new angularclient

Най- новата команда ще генерира цялата структура заявление в рамките на angularclient директория.

3.3. Входна точка на ъгловото приложение

Ако погледнем в папката angularclient , ще видим, че Angular CLI ефективно е създал цял проект за нас.

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.

След като приложението Spring Boot е стартирано, нека отворим командна конзола и напишем следната команда:

ng serve --open

Това ще стартира сървъра за разработка на живо на Angular и ще отвори браузъра на // localhost: 4200 .

Трябва да видим лентата за навигация с бутоните за изброяване на съществуващи обекти и за добавяне на нови. Ако щракнем върху първия бутон, трябва да видим под лентата за навигация таблица със списъка на обектите, съхранявани в базата данни:

По същия начин, щракването на втория бутон ще покаже HTML формата за запазване на нов обект:

5. Заключение

В този урок научихме как да изградим основно уеб приложение с Spring Boot и Angular .

Както обикновено, всички примерни кодове, показани в този урок, са достъпни в GitHub.