Скачать или смотреть Resolving the CORS Issue in Angular with Spring Backend

Learn how to tackle the `CORS` problem when accessing REST endpoints in Angular connected to a Spring backend. Follow our step-by-step solution to get your application running smoothly again.
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Resolving the CORS Issue in Angular with Spring Backend: A Comprehensive Guide

If you've been developing a web application that uses an Angular client to access a Spring backend, you may encounter CORS (Cross-Origin Resource Sharing) issues. These errors can be frustrating, especially when everything seemed to be working just fine earlier. In this post, we’ll explore a common situation involving CORS problems, particularly in the context of using OAuth2 for authentication.

Understanding the CORS Problem

In a typical web application, the browser enforces security by restricting cross-origin HTTP requests initiated from scripts. This means that if your Angular app runs on http://localhost:4200 and tries to interact with your Spring backend on http://localhost:8080, the browser may block the request due to CORS policy if they aren’t configured correctly.

The Initial Setup

You previously configured your Spring backend to allow requests from the Angular client using the following annotation on your controller:

[[See Video to Reveal this Text or Code Snippet]]

This should typically work. However, adding Spring Security or HTTP interceptors in your Angular app may change the dynamics and lead to authentication issues.

Diagnosing the CORS Issue

After implementing security, you might experience errors like:

[[See Video to Reveal this Text or Code Snippet]]

Common Scenarios to Consider

Token Authorization: If you're adding a Bearer token to your requests but the CORS policy does not allow the authorization headers, the request will be blocked.

Proxy Configuration: When using Angular's HttpClient, often a proxy configuration is necessary to redirect requests to the backend.

Suggested Solutions

To resolve the CORS issue, consider the following structured approach:

1. Update Proxy Configuration

You need to ensure that your Angular application is using a proper proxy configuration file, such as proxy.config.js. Here’s an example:

[[See Video to Reveal this Text or Code Snippet]]

Make sure your angular.json includes this configuration:

[[See Video to Reveal this Text or Code Snippet]]

2. Check Security Configurations

After implementing Spring Security, ensure that your CORS configuration allows specific headers. An example setup in your Spring security configuration could look like this:

[[See Video to Reveal this Text or Code Snippet]]

3. Testing through Postman

If you can successfully send requests via Postman but not through your Angular app, double-check the headers. Make sure that your Angular application accurately replicates the requests, including the necessary authentication headers.

4. Console Logging for Debugging

Use console.log to log the outgoing requests and confirm whether the headers are applied correctly:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

CORS issues can seem mind-boggling, particularly when they arise after integrating new features such as security. By understanding the core components of CORS and ensuring that both the server and client configurations are correctly set, you can resolve these errors.

Implementing the above solutions should restore smooth interaction between your Angular frontend and Spring backend, enabling you to continue developing your web application successfully.

Feel free to share your experiences and any other solutions that worked for you in the comments below!