Resolving File Upload Issues in Angular 8 with Spring Boot and Spring Security

Learn how to successfully upload files from Angular 8 to Spring Boot while using Spring Security, by resolving common configuration issues that arise.
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This video is based on the question https://stackoverflow.com/q/71773871/ asked by the user 'Dreamweaver2012' ( https://stackoverflow.com/u/18700668/ ) and on the answer https://stackoverflow.com/a/71774748/ provided by the user 'Marvin Ajcuc' ( https://stackoverflow.com/u/6328963/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Troubleshooting File Uploads from Angular to Spring Boot with Spring Security

When you add Spring Security to your Spring Boot backend, some functionalities can break — particularly file uploads. If you have implemented a file upload feature in your Angular 8 application and suddenly it stops working after integrating Spring Security, you're not alone. It's a common scenario that many developers face. In this guide, we'll explore the issue, identify the underlying cause, and provide a comprehensive solution to get your file upload feature working again.

Understanding the Problem

After introducing Spring Security into your Spring Boot application, you noticed that the file upload feature ceased to function. While other GET and POST requests still work well when authenticated, the file upload results in errors. The backend does not reach the designated method in the controller, and it could be due to the way Angular is sending the request or how Spring Security is configured to handle it.

Key Symptoms

With withCredentials: true: The file upload fails silently; the intended method is never invoked.

Without withCredentials: true: You encounter a MultipartException, which indicates the request isn't processed as a multipart file upload.

Analyzing the Solution

One major culprit of the issue lies in the HTTP headers being set in the Angular application. Particularly, the Content-Type header is crucial for file handling in multipart uploads.

Step-by-Step Fix

Inspect the Angular Interceptor:

In the Angular HttpInterceptorService, you currently set the Content-Type header to application/json. However, for file uploads, this needs to be set to multipart/form-data. Remove or modify this header.

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Verify the File Upload Method in Angular:

Ensure that you're correctly forming the FormData object and using it in the HttpRequest. It seems you already did this part correctly, but double-check especially when appending other parameters.

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Spring Security Configuration:

Make sure that your Spring Security configuration allows multipart requests. If you have CSRF protection enabled by default, it may prevent file uploads. Since you've disabled CSRF for testing, ensure that this aspect doesn't block the upload in a production environment. Pay attention to endpoint permissions as well.

Check the Network Response:

If you've set withCredentials: true, investigate the actual HTTP response for that request using the browser's developer tools. Ensure it includes the necessary headers and has the correct response code.

Testing:

Make small changes one at a time, and test your file upload after each adjustment to determine what works. This practice makes it easier to catch what breaks the functionality and enhances your debugging process.

Conclusion

Integrating security into your applications can sometimes lead to unexpected hurdles, especially with file uploads. By carefully examining the HTTP headers your Angular application is sending and ensuring that your Spring Boot application is correctly configured to handle multipart requests, you can troubleshoot and resolve these issues effectively.

By following these steps, you should be able to restore your file upload functionality while maintaining your application's security. Happy coding!

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