@ConditionalOnBean不起作用

结论

1， Spring 是先处理配置类，再加载 Bean的，所以不要@ConditionalOnBean和@Configuration一起用；
2，使用@AutoConfigureAfter指定@Configuration的先后初始化顺序；

参考内容

@AutoConfigureAfter 是有用的，但是 Spring 的配置解析和 Bean 的加载并不是同时发生的，而是有先后的：
//ConfigurationClassPostProcessor.java
//第261行
public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
 //省略部分代码

 //先解析所有的配置
 parser.parse(candidates);

 //省略部分代码

 //再根据配置将类加载到Spring中
 this.reader.loadBeanDefinitions(configClasses);

 //省略部分代码
}
从上边的代码可以看到 Spring 是先处理配置类，再加载 Bean 的，所以配置上使用 @ConditionalOnBean 注解，都是无效的。

评论：
自动配置上不能用@ConditionalOnBean注解，就像文章里说的，配置类是先加载的，除非你@ConditionalOnBean里的东西也是个配置类。 Spring的配置类上这个注解能生效是因为其中的那个bean是spring通过注解来引入的（抱歉一时间找不到例子了），通过注解引入的bean在配置类加载的时候就会导入。在普通类上加@ConditionalOnBean是可以的，但要注意生成的顺序

https://my.oschina.net/icebergxty/blog/3153051

The javadoc for @ConditionalOnBean describes it as:

Conditional that only matches when the specified bean classes and/or names are already contained in the BeanFactory.

In this case, the key part is "already contained in the BeanFactory". Your own configuration classes are considered before any auto-configuration classes. This means that the auto-configuration of the MetricsEndpoint bean hasn't happened by the time that your own configuration is checking for its existence and, as a result, your MetricsFormatEndpoint bean isn't created.

One approach to take would be to create your own auto-configuration class for your MetricsFormatEndpoint bean and annotate it with @AutoConfigureAfter(EndpointAutoConfiguration.class). That will ensure that its conditions are evaluated after the MetricsEndpoint bean has been defined.

https://stackoverflow.com/questions/31799855/spring-annotation-conditionalonbean-not-working