What is purpose of @ConditionalOnProperty annotation?

Question

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").

Answer 1

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.

Answer 2

In case you are using this property on TYPE-level, i.e. on one of your @Configuration classes... Keep in mind that in such case the annotation is evaluated/checked against the default properties file, i.e. application.properties

@ConditionalOnProperty on TYPE level w/ @Configuration