Скачать или смотреть How to Defer Initialization of a BeanPostProcessor in Spring Boot

Learn how to manage the instantiation of `BeanPostProcessor` to control bean creation order in Spring Boot applications.
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This video is based on the question https://stackoverflow.com/q/69052004/ asked by the user 'Brady Goldman' ( https://stackoverflow.com/u/1672681/ ) and on the answer https://stackoverflow.com/a/69057925/ provided by the user 'Brady Goldman' ( https://stackoverflow.com/u/1672681/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Solving BeanPostProcessor Initialization Issues in Spring Boot

When developing applications using Spring Boot, you may encounter an issue related to the initialization order of beans, particularly when working with BeanPostProcessor. This post addresses a common problem: what to do when you want to introduce a BeanPostProcessor but defer its instantiation to maintain control over bean creation order.

The Problem: Unexpected Auto-Scanning

Spring Boot is designed to automatically scan for components, including implementations of BeanPostProcessor, which can lead to premature instantiation. This can disrupt the order in which beans are created and can inadvertently lead to issues, especially in applications that rely on late-initialized components like Jersey Client filters.

In this case, the goal is to ensure that our custom BeanPostProcessor, designed for injecting Jersey Client filters into lazy-loaded clients, is instantiated only when we need it, preserving the bean lifecycle as intended.

Understanding the ClientFilterInjector Class

Here's a quick recap of the original code for the ClientFilterInjector class which implements BeanPostProcessor:

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

The issue here is that this class gets auto-scanned, which is not ideal in certain scenarios where we want better control over the bean initialization sequence.

The Solution: Using an Anonymous Class

One effective solution to defer the instantiation of your BeanPostProcessor is to implement it as an anonymous class. This technique allows you to control when the processor is added to the application context without being auto-scanned upon application startup.

Implementation Steps

Create an Anonymous Instance: Instead of declaring ClientFilterInjector as a standalone class, encapsulate it in an anonymous class when you add it to the application context.

Add to Application Context: Utilize the getBeanFactory() method of the ConfigurableApplicationContext to add the anonymous BeanPostProcessor.

Here's how you can do it:

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

Benefits of This Approach

Control Over Initialization: By deferring instantiation, you regain control over when the BeanPostProcessor is invoked in the application's lifecycle.

Flexible Integration: This method allows for ad-hoc integration of your processing logic, providing flexibility for different scenarios.

Conclusion

Dealing with bean initialization conflicts in Spring Boot can be tricky, especially when working with BeanPostProcessor. By implementing your processor as an anonymous class and adding it to the application context explicitly, you can effectively manage the order of bean creation without falling prey to auto-scanning. This is a simple yet powerful technique that can help streamline your application's functionality and ensure that components are initialized in the proper sequence.

If you're regularly working with Spring Boot and Jersey Client, understanding these subtleties can make a significant difference in your application's performance and reliability.