@ConditionalOnProperty 注释的目的是什么? [英] What is purpose of @ConditionalOnProperty annotation?

问题描述

我刚刚修改了spring boot的配置，遇到了

I just modified spring boot configuration, and encountered

@ConditionalOnProperty(prefix = "spring.social.", value = "auto-connection-views") 

来自 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");
}

我不明白这个注释的目的.我想这可能只有在属性值存在时才能使用 bean(例如spring.social"、auto-connection-views").

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").

推荐答案

注解用于根据属性的配置有条件地创建 Spring bean.在您在问题中显示的用法中，仅当 spring.social.auto-connection-views 属性存在且其值不是 false 时才会创建 bean>.这意味着，要创建此 View bean，您需要设置 spring.social.auto-connection-views 属性，并且它必须具有除假的.

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.

您可以在整个 Spring Boot 代码库中找到此注释的许多其他用途.另一个例子是:

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);
}

注意matchIfMissing的使用.在这种情况下，如果 spring.rabbitmq.dynamic 属性存在并且其值不是 false 或 该属性根本不存在.这使得 bean 的创建选择退出，而不是问题中选择加入的示例.

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.

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