spring boot ConditionalOnMissingBean 问题

[mgzu]

项目引用了业务日志库，使用注解 @EnableLogRecord 来自动配置库相关的 Bean ，其中有个获取当前操作人的 Bean 有 @ConditionalOnMissingBean 注解，当自定义该 Bean 的时候，以下第一种情况符合预期，第二种会启动失败，想请教下各位其中的原因及解决办法

库源码：com.mzt.logapi.starter.configuration.LogRecordProxyAutoConfiguration

    @Bean
    @ConditionalOnMissingBean(IOperatorGetService.class)
    @Role(BeanDefinition.ROLE_APPLICATION)
    public IOperatorGetService operatorGetService() {
        return new DefaultOperatorGetServiceImpl();
    }

一. 在 spring boot 启动类添加 @EnableLogRecord ，@ConditionalOnMissingBean 有效

@EnableLogRecord(tenant = "temp")
@SpringBootApplication
public class DemoApplication {

	public static void main(String[] args) {
		SpringApplication.run(DemoApplication.class, args);
	}

}

二. 在配置类添加 @EnableLogRecord ，@ConditionalOnMissingBean 无效，启动报错

@EnableLogRecord(tenant = "temp")
@Configuration(proxyBeanMethods = false)
public class LogRecordConfiguration {
    public LogRecordConfiguration() {
    }

    /**
     * 自定义获取操作人
     */
    @Bean
    public IOperatorGetService operatorGetService() {
        return () -> {
            Operator operator = new Operator();
            operator.setOperatorId("test");
            return operator;
        };
    }

}

repo: https://github.com/TheLastSunset/spring-boot-ConditionalOnMissingBean-issues.git

[panpanpan]

spring bean 初始化顺序的问题，如果 LogRecordConfiguration 比 LogRecordProxyAutoConfiguration 先初始化，@ConditionalOnMissingBean 就可以生效，反之 LogRecordProxyAutoConfiguration 先初始化的话，执行到 @ConditionalOnMissingBean(IOperatorGetService.class)的时候就会返回 true ，导致 DefaultOperatorGetServiceImpl 被注入，后面再到 LogRecordConfiguration 的时候就冲突了


官网文档
https://docs.spring.io/spring-boot/docs/current/api/org/springframework/boot/autoconfigure/condition/ConditionalOnMissingBean.html

The condition can only match the bean definitions that have been processed by the application context so far and, as such, it is strongly recommended to use this condition on auto-configuration classes only. If a candidate bean may be created by another auto-configuration, make sure that the one using this condition runs after.

[mgzu]

@panpanpan 是的，@ConditionalOnMissingBean 会检查容器中是否存在对应的 BeanDefinition ，存在则跳过，
见 https://github.com/spring-projects/spring-framework/blob/5.3.x/spring-context/src/main/java/org/springframework/context/annotation/ConfigurationClassBeanDefinitionReader.java#L194 。

而 BeanDefinition 则于以下位置加载
https://github.com/spring-projects/spring-framework/blob/5.3.x/spring-context/src/main/java/org/springframework/context/annotation/ConfigurationClassPostProcessor.java#L343

在情况一中，configClasses 顺序是：0. LogRecordConfiguration ，1. LogRecordProxyAutoConfiguration
情况二中，configClasses 顺序是：0. LogRecordProxyAutoConfiguration ，1. LogRecordConfiguration
因此会导致情况一启动成功，情况二启动失败
而 configClasses 则跟 spring 扫描类有关，目前没找到比较好的控制扫描类顺序或 BeanDefinition 注册顺序的方法