I just modified spring boot configuration, and encountered
@ConditionalOnProperty(prefix = "spring.social.", value = "auto-connection-views")
from org.springframework.boot.autoconfigure.social.TwitterAutoConfiguration
@Bean(name = { "connect/twitterConnect", "connect/twitterConnected" })
@ConditionalOnProperty(prefix = "spring.social.", value = "auto-connection-views")
public View twitterConnectView() {
return new GenericConnectionStatusView("twitter", "Twitter");
}
I don't understand purpose of this annotation. I guess this might be enable to use bean only if property value exist(e.g. "spring.social", "auto-connection-views").
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.
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.