java - Bean中冲突时Spring Bean创建异常
问题描述
以下是我们项目中使用的通用启动器中的代码。
@ConditionalOnProperty(prefix = "some.prefix", value = "some-enable")
@EnableConfigurationProperties(value = {
SomeProperties.class,
})
@Configuration
class RabbitGenericValueConfiguration {
@Autowired
public void setuoRabbit(AmqpAdmin admin) {
admin.declareExchange(exchange());
}
@ConditionalOnProperty(prefix = "existing.property", value = "setup")
@ConditionalOnMissingBean
@Bean
Exchange exchange() {
return ExchangeBuilder.topicExchange(properties.getExchange())
.build();
}
}
在我们的服务中,我们需要创建一个自定义交换,但是每当我们添加以下代码时,都会发生以下错误
@Configuration
public class CustomConfiguration {
@Bean
public DirectExchange direct() {
return new DirectExchange("test.direct");
}
}
例外是
org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'exchange' available
at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeanDefinition(DefaultListableBeanFactory.java:687)
at org.springframework.beans.factory.support.AbstractBeanFactory.getMergedLocalBeanDefinition(AbstractBeanFactory.java:1207)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:284)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.obtainBeanInstanceFromFactory(ConfigurationClassEnhancer.java:389)
at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:361)
at com.something.RabbitGenericValueConfiguration$$EnhancerBySpringCGLIB$$2df2c1f1.exchange(<generated>)
at com.something.RabbitGenericValueConfiguration.setuoRabbit(RabbitGenericValueConfiguration.java:145)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
问题是为什么应用程序在自定义交换不存在时启动,而在自定义交换存在时失败。
解决方案
您声明了exchange
命名的 bean,例如:
@ConditionalOnProperty(prefix = "existing.property", value = "setup")
@ConditionalOnMissingBean
@Bean
Exchange exchange() {
return ExchangeBuilder.topicExchange(properties.getExchange())
.build();
}
听起来这两个声明的 bean 是从Exchange
类派生的。因此,@ConditionalOnMissingBean
如果首先实例化该 bean,则注释的存在会阻止该 bean 被实例化:
@Bean
public DirectExchange direct() {
return new DirectExchange("test.direct");
}
正如@ConditionalOnMissingBean
javadoc所说(重点是我的):
仅当指定的 bean 类和/或名称尚未包含在 BeanFactory中时才匹配的条件。
@ConditionalOnMissingBean
如果您希望 Spring 实例化两者,您可能应该删除。