Fixing JwtRequestFilter Proxy Errors in Spring Security by Managing Bean Instantiation

Описание: Learn how to resolve Spring proxy errors caused by final methods in JwtRequestFilter by avoiding component scanning and manually instantiating the filter in your security configuration.
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This video is based on the question https://stackoverflow.com/q/79483174/ asked by the user 'Aucta Dev' ( https://stackoverflow.com/u/28143752/ ) and on the answer https://stackoverflow.com/a/79483195/ provided by the user 'Aucta Dev' ( https://stackoverflow.com/u/28143752/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Problem

When integrating a custom JWT filter in a Spring Security setup, you might encounter errors like:

"Unable to proxy interface-implementing method ... because it is marked as final, consider using interface-based JDK proxies instead."

This occurs because Spring tries to create a proxy of a class (OncePerRequestFilter) whose key methods are declared final, which can't be proxied by CGLIB effectively.

Why This Happens

OncePerRequestFilter has final methods such as doFilter that can't be overridden or proxied.

If your JWT filter class is annotated with @ Component or @ Service, Spring might attempt to create a proxy of it.

Proxy creation fails due to the final methods, leading to application startup errors.

The Concise Solution

1. Avoid Annotating the Filter as a Spring Bean

Remove @ Component or any stereotype annotation from your JwtRequestFilter class:

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

2. Instantiate the Filter Manually in Security Configuration

Instead of injecting the filter, create it as an explicit bean or instantiate it inside your SecurityConfig:

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

Key Takeaways

Don’t rely on component scanning for filters extending classes with final methods.

Manually instantiate and register the filter in your security configuration.

This approach prevents Spring from trying to create a proxy around final methods that causes startup failures.

Summary

Proxy errors with JwtRequestFilter stem from attempting to proxy a OncePerRequestFilter subclass with final methods. The best practice is to avoid @ Component on the filter and instead instantiate it manually in your security config. This keeps proxying out of the equation and ensures smooth startup.