How to connect Java backend with Angular or React?

 

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In a Java full stack project, managing databases involves several key steps and tools to ensure smooth data storage, retrieval, and maintenance across the application.

To connect a Java backend (e.g., Spring Boot) with a frontend built in Angular or React, you use HTTP-based communication—typically REST APIs. Here’s a clear guide to how it works and how to set it up:

✅ 1. Build the Java Backend (e.g., using Spring Boot)

Create RESTful APIs using @RestController in Spring Boot:

java

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@RestController

@RequestMapping("/api/users")

public class UserController {

    

    @GetMapping

    public List<User> getAllUsers() {

        return userService.getUsers();

    }

    @PostMapping

    public User createUser(@RequestBody User user) {

        return userService.saveUser(user);

    }

}

Run the backend on a port (default is http://localhost:8080).

✅ 2. Create the Frontend (Angular or React)

In Angular:

Use Angular’s HttpClient to call the API.

typescript

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// user.service.ts

getUsers(): Observable<User[]> {

  return this.http.get<User[]>('http://localhost:8080/api/users');

}

In React:

Use fetch or Axios to call the API.

javascript

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// Using fetch

useEffect(() => {

  fetch('http://localhost:8080/api/users')

    .then(res => res.json())

    .then(data => setUsers(data));

}, []);

✅ 3. Handle CORS (Cross-Origin Resource Sharing)

By default, browser will block frontend-backend calls on different ports.

In Spring Boot, enable CORS:

java

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@CrossOrigin(origins = "http://localhost:4200") // Angular default port

Or configure globally in Spring:

java

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@Configuration

public class WebConfig implements WebMvcConfigurer {

  @Override

  public void addCorsMappings(CorsRegistry registry) {

    registry.addMapping("/**")

            .allowedOrigins("http://localhost:3000") // React

            .allowedMethods("*");

  }

}

✅ 4. Run Both Apps

Backend: mvn spring-boot:run or using your IDE

Angular: ng serve (port 4200)

React: npm start (port 3000)

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