refactor: BeanPostProcessor should avoid dependencies on other beans

[DanielLiu1123]

This PR primarily addresses two issues:

• LoadBalancerRestClientBuilderBeanPostProcessor and LoadBalancerWebClientBuilderBeanPostProcessor are BeanPostProcessor and should not depend on other beans. This could lead to the premature initialization of Configuration classes, potentially resulting in warnings like the following:

2023-12-02T14:20:26.574+08:00  WARN 85116 --- [load-balancer] [    Test worker] trationDelegate$BeanPostProcessorChecker : Bean 'org.springframework.cloud.client.loadbalancer.reactive.LoadBalancerBeanPostProcessorAutoConfiguration' of type [org.springframework.cloud.client.loadbalancer.reactive.LoadBalancerBeanPostProcessorAutoConfiguration] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying). The currently created BeanPostProcessor [loadBalancerWebClientBuilderBeanPostProcessor] is declared through a non-static factory method on that class; consider declaring it as static instead.
2023-12-02T14:20:26.576+08:00  WARN 85116 --- [load-balancer] [    Test worker] trationDelegate$BeanPostProcessorChecker : Bean 'org.springframework.cloud.client.loadbalancer.reactive.LoadBalancerBeanPostProcessorAutoConfiguration$ReactorDeferringLoadBalancerFilterConfig' of type [org.springframework.cloud.client.loadbalancer.reactive.LoadBalancerBeanPostProcessorAutoConfiguration$ReactorDeferringLoadBalancerFilterConfig] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying). Is this bean getting eagerly injected into a currently created BeanPostProcessor [loadBalancerWebClientBuilderBeanPostProcessor]? Check the corresponding BeanPostProcessor declaration and its dependencies.
2023-12-02T14:20:26.579+08:00  WARN 85116 --- [load-balancer] [    Test worker] trationDelegate$BeanPostProcessorChecker : Bean 'reactorDeferringLoadBalancerExchangeFilterFunction' of type [org.springframework.cloud.client.loadbalancer.reactive.DeferringLoadBalancerExchangeFilterFunction] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying). Is this bean getting eagerly injected into a currently created BeanPostProcessor [loadBalancerWebClientBuilderBeanPostProcessor]? Check the corresponding BeanPostProcessor declaration and its dependencies.

• The default value for spring.cloud.loadbalancer.retry.enabled is true, but this has not been consistently applied in some code.

[spencergibb]

Not sure we can make these breaking changes in minor releases.

[DanielLiu1123]

Including these changes in version 4.1.0 (before the GA) seems reasonable.

[spencergibb]

It's a minor release. We won't make breaking changes

[DanielLiu1123]

These changes will be accepted?

[spencergibb]

please be patient

[app2smile]

After upgrade to Spring Cloud 2023.0.0 , when I start up my application

[ WARN ]  PostProcessorRegistrationDelegate$BeanPostProcessorChecker.postProcessAfterInitialization(429):  Bean 'org.springframework.cloud.client.loadbalancer.LoadBalancerAutoConfiguration$LoadBalancerInterceptorConfig' of type [org.springframework.cloud.client.loadbalancer.LoadBalancerAutoConfiguration$LoadBalancerInterceptorConfig] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying). The currently created BeanPostProcessor [lbRestClientPostProcessor] is declared through a non-static factory method on that class; consider declaring it as static instead.

[ WARN ]  PostProcessorRegistrationDelegate$BeanPostProcessorChecker.postProcessAfterInitialization(437):  Bean 'org.springframework.cloud.loadbalancer.config.BlockingLoadBalancerClientAutoConfiguration' of type [org.springframework.cloud.loadbalancer.config.BlockingLoadBalancerClientAutoConfiguration] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying). Is this bean getting eagerly injected into a currently created BeanPostProcessor [lbRestClientPostProcessor]? Check the corresponding BeanPostProcessor declaration and its dependencies.

[crmky]

Unfortunately the issue was not addressed in Spring Cloud 2023 release. Similar to @app2smile, our applications generates many warnings during startup after upgrade to Spring Boot 3.2 with Spring Cloud 2023.

Those warnings are caused by changes introduced by #1294. The new introduced LoadBalancerRestClientBuilderBeanPostProcessor depends on either RetryLoadBalancerInterceptor or LoadBalancerInterceptor, which causes the dependencies in the whole dependency chain get early initialized.

It will be good if we can address those warnings in the next release.

[OlgaMaciaszek]

Thanks for creating the PR @DanielLiu1123. As indicated in this comment, while the warnings provide information, we have not noticed this is causing any bugs. In any case, we can consider the change proposal for a future major (date or release train number not set yet), however, please create a separate PR with changes for retry behaviour and a comment with your justification for it, and remove those changes from this one, as we might be considering it independently.

[DanielLiu1123]

I'd be happy to do that.

[OlgaMaciaszek]

Hello @DanielLiu1123 please keep in mind, that I've already created a PR related to changes in the post-processor after determining there was a bug: #1319, so please just create a separate PR with your retry logic changes, and we will review it.

[DanielLiu1123]

Already done, #1321

[OlgaMaciaszek]

Thanks @DanielLiu1123