How to Connect an Angular Frontend with a Spring Boot Backend

Introduction
Integrating an Angular frontend with a Spring Boot backend is a common approach for building full-stack web applications. Angular, a powerful frontend framework, communicates with the backend via HTTP requests, while Spring Boot provides a robust REST API to handle business logic and data persistence.

In this guide, we will cover:

• Setting up the Spring Boot backend
• Creating the Angular frontend
• Connecting Angular with Spring Boot using HTTP requests

Step 1: Set Up the Spring Boot Backend

1.1 Create a Spring Boot Application
You can generate a Spring Boot project using Spring Initializr:

• Dependencies: Spring Web, Spring Boot DevTools, Spring Data JPA, H2 Database (or MySQL/PostgreSQL if needed).
• Packaging: Jar

Once the project is generated, extract and open it in an IDE (e.g., IntelliJ IDEA or VS Code).

1.2 Create a Simple REST API
Modify src/main/java/com/example/demo/controller/UserController.java:

java
@RestController
@RequestMapping("/api/users")
@CrossOrigin(origins = "http://localhost:4200") // Allow Angular to access this API
public class UserController {

@GetMapping
public ResponseEntity<String> getUsers() {
    return ResponseEntity.ok("Hello from Spring Boot!");
}

}

1.3 Run the Spring Boot Application
Use the command:
mvn spring-boot:run

Your backend should be running on http://localhost:8080.

Step 2: Create the Angular Frontend

2.1 Generate an Angular Project
Run the following command:
ng new angular-app
cd angular-app

2.2 Install Angular HTTP Client
Run:
npm install @angular/common

Then, open src/main.ts and ensure you provide the HTTP client globally:

typescript
import { provideHttpClient } from '@angular/common/http';
import { bootstrapApplication } from '@angular/platform-browser';
import { AppComponent } from './app/app.component';

bootstrapApplication(AppComponent, {
providers: [provideHttpClient()],
}).catch(err => console.error(err));

Step 3: Connect Angular to Spring Boot

3.1 Create an Angular Service to Call the API
Run:
ng generate service services/user

Modify src/app/services/user.service.ts:

typescript
import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable } from 'rxjs';

@Injectable({
providedIn: 'root'
})
export class UserService {
private apiUrl = 'http://localhost:8080/api/users';

constructor(private http: HttpClient) {}

getUsers(): Observable {
return this.http.get(this.apiUrl, { responseType: 'text' });
}
}

3.2 Use the Service in a Component
Modify src/app/app.component.ts:

typescript
import { Component, OnInit } from '@angular/core';
import { UserService } from './services/user.service';

@Component({
selector: 'app-root',
template: 'h1 {{ message }} h1',
})
export class AppComponent implements OnInit {
message: string = '';

constructor(private userService: UserService) {}

ngOnInit() {
this.userService.getUsers().subscribe(data => this.message = data);
}
}

Step 4: Run and Test the Integration

4.1 Start the Angular Application
Run:
ng serve

Your Angular app should be running on http://localhost:4200.

4.2 Verify the Connection

• Open the browser and go to http://localhost:4200.
• You should see "Hello from Spring Boot!" displayed on the page.

Conclusion
By following these steps, you have successfully connected an Angular frontend with a Spring Boot backend. You can now extend this setup by adding authentication, CRUD operations, and database interactions.