What is purpose of @ConditionalOnProperty annotation?

http://stackoverflow.com/questions/26394778/what-is-purpose-of-conditionalonproperty-annotation

****************************************************

I just modified spring boot configuration, and encountered

@ConditionalOnProperty(prefix = "spring.social.", value = "auto-connection-views") from org.springframework.boot.autoconfigure.social.TwitterAutoConfiguration.java

@Bean(name = { "connect/twitterConnect", "connect/twitterConnected" })
@ConditionalOnProperty(prefix = "spring.social.", value = "auto-connection-views")
public View twitterConnectView() {
return new GenericConnectionStatusView("twitter", "Twitter");
}

answers

The annotation is used to conditionally create a Spring bean depending on the configuration of a property. In the usage you've shown in the question the bean will only be created if the

spring.social.auto-connection-views

property exists and it has a value other than

false

. This means that, for this

View

bean to be created, you need to set the

spring.social.auto-connection-views

property and it has to have a value other than false.

如果property

spring.social.auto-connection-views

存在,并且值不为false,创建bean.

You can find numerous other uses of this annotation throughout the Spring Boot code base. Another example is:

@ConditionalOnProperty(prefix = "spring.rabbitmq", name = "dynamic", matchIfMissing = true)
public AmqpAdmin amqpAdmin(CachingConnectionFactory connectionFactory) {
return new RabbitAdmin(connectionFactory);
}

Note the use of

matchIfMissing

. In this case the

AmqpAdmin

bean will be created if the

spring.rabbitmq.dynamic

property exists and has a value other than

false

or the property doesn't exist at all. This makes the creation of the bean opt-out rather than the example in the question which is opt-in.

如果property spring.rabbitmq.dynamic存在，并且值不为false,创建bean

matchIfMissing = true， 如果改属性条目不存在，创建bean.