{"id":65358,"date":"2020-08-31T15:31:10","date_gmt":"2020-08-31T15:31:10","guid":{"rendered":"https:\/\/www.baeldung.com\/?p=86273"},"modified":"2020-08-31T15:31:10","modified_gmt":"2020-08-31T15:31:10","slug":"the-spring-conditionalonproperty-annotation","status":"publish","type":"post","link":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/2020\/08\/31\/the-spring-conditionalonproperty-annotation\/","title":{"rendered":"The Spring @ConditionalOnProperty Annotation"},"content":{"rendered":"

<\/p>\n

1. Overview<\/h2>\n
<\/div>\n

In this short tutorial, we’re going to shed light on the main purpose of the @ConditionalOnProperty<\/em> annotation<\/strong>.<\/p>\n

First, we’ll start with a bit of background about what @ConditionalOnProperty<\/em> is. Then, we’ll look at some practical examples to help understand how it works and what features it brings.<\/p>\n

2. The Purpose of @ConditionalOnProperty<\/em><\/h2>\n
<\/div>\n

Typically, when developing Spring-based applications, we may need to create some beans<\/a> conditionally based on the presence and the value of a configuration property<\/strong>.<\/p>\n

For example, we may want to register a DataSource<\/em> bean to point to a production or a test database depending on if we set a property value to “prod” or “test”.<\/p>\n

Fortunately, achieving that isn’t as hard as it might look upon first glance. The Spring framework provides the @ConditionalOnProperty<\/em> annotation<\/a> precisely for this purpose.<\/p>\n

In short, the @ConditionalOnProperty <\/em>enables bean registration only if an environment property is present and has a specific value. By default, the specified property must be defined and not equal to false<\/em>.<\/p>\n

Now that we’re familiar with the purpose of the @ConditionalOnProperty<\/em> annotation, let’s dig deeper to see how it works.<\/p>\n

3. The @ConditionalOnProperty<\/em> Annotation in Practice<\/h2>\n
<\/div>\n

To exemplify the use of @ConditionalOnProperty, <\/em>we’ll develop a basic notification system. To keep things simple for now, let’s assume that we want to send email notifications.<\/p>\n

First, we’ll need to create a simple service to send a notification message. For instance, consider the NotificationSender<\/em> interface:<\/p>\n

public interface NotificationSender {\r\n    String send(String message);\r\n}<\/code><\/pre>\n
Next, let’s provide an implementation of the NotificationSender<\/em> interface to send our emails:<\/p>\n
public class EmailNotification implements NotificationSender {\r\n    @Override\r\n    public String send(String message) {\r\n        return \"Email Notification: \" + message;\r\n    }\r\n}<\/code><\/pre>\n
Now, let’s see how to make use of the @ConditionalOnProperty<\/em> annotation. Let’s configure the NotificationSender<\/em> bean in such a way that it will only be loaded if the property notification.service<\/em> is defined<\/strong>:<\/p>\n
@Bean(name = \"emailNotification\")\r\n@ConditionalOnProperty(prefix = \"notification\", name = \"service\")\r\npublic NotificationSender notificationSender() {\r\n    return new EmailNotification();\r\n}<\/code><\/pre>\n
As we can see, the prefix<\/em> and name<\/em> attributes are used to denote the configuration property that should be checked<\/strong>.<\/p>\n
Finally, we need to add the last missing piece of the puzzle. Let’s define our custom property in the application.properties<\/em> file<\/a>:<\/p>\n
notification.service=email<\/code><\/pre>\n
4. Advanced Configuration<\/h2>\n
<\/div>\n
As we have already learned, the @ConditionalOnProperty<\/em> annotation allows us to register beans conditionally depending on the presence of a configuration property.<\/p>\n
However, we can do more than just that with this annotation.<\/em> So, let’s explore!<\/p>\n
Let’s suppose we want to add another notification service \u2014 for example, a service that will allow us to send SMS notifications.<\/p>\n
To do that, we need to create another NotificationSender <\/em>implementation:<\/p>\n
public class SmsNotification implements NotificationSender {\r\n    @Override\r\n    public String send(String message) {\r\n        return \"SMS Notification: \" + message;\r\n    }\r\n}<\/code><\/pre>\n
Since we have two implementations, let’s see how we can use @ConditionalOnProperty <\/em>to load the right NotificationSender<\/em> bean conditionally.<\/p>\n
For this purpose, the annotation provides the havingValue <\/em>attribute. Quite interestingly, it<\/strong> defines the value that a property must have in order for a specific bean to be added to the Spring container<\/a><\/strong>.<\/p>\n
Now, let’s specify under what condition we want to register the SmsNotification<\/em> implementation in the context:<\/p>\n
@Bean(name = \"smsNotification\")\r\n@ConditionalOnProperty(prefix = \"notification\", name = \"service\", havingValue = \"sms\")\r\npublic NotificationSender notificationSender2() {\r\n    return new SmsNotification();\r\n}<\/code><\/pre>\n
With the help of the havingValue<\/em> attribute, we made it clear that we want to load SmsNotification<\/em>\u00a0only when notification.service <\/em>is set to sms<\/em>.<\/p>\n
It’s worth mentioning that @ConditionalOnProperty <\/em>has another attribute called matchIfMissing<\/em><\/a>. This attribute specifies whether the condition should match in case the property is not available<\/strong>.<\/p>\n
Now, let’s put all the pieces together and write a simple test case to confirm that everything works as expected:<\/p>\n
@Test\r\npublic void whenValueSetToEmail_thenCreateEmailNotification() {\r\n    this.contextRunner.withPropertyValues(\"notification.service=email\")\r\n        .withUserConfiguration(NotificationConfig.class)\r\n        .run(context -> {\r\n            assertThat(context).hasBean(\"emailNotification\");\r\n            NotificationSender notificationSender = context.getBean(EmailNotification.class);\r\n            assertThat(notificationSender.send(\"Hello From Baeldung!\")).isEqualTo(\"Email Notification: Hello From Baeldung!\");\r\n            assertThat(context).doesNotHaveBean(\"smsNotification\");\r\n        });\r\n}<\/code><\/pre>\n
5. Conclusion<\/h2>\n
<\/div>\n
In this short tutorial, we highlighted the purpose of using the @ConditionalOnProperty <\/em>annotation. <\/em>Then, we showcased, through a practical example, how to use it to load Spring beans conditionally.<\/p>\n
As always, the full source code of this tutorial is available over on GitHub<\/a>.<\/p>\n
The post The Spring @ConditionalOnProperty Annotation<\/a> first appeared on Baeldung<\/a>.<\/p>\n
\"\"<\/p>\n
<\/a> <\/a> <\/a> <\/a> <\/a> <\/a> <\/a> <\/a> <\/div>\n\n
\\\"IT\u96fb\u8166\u88dc\u7fd2
\u7acb\u523b\u8a3b\u518a\u53ca\u5831\u540d\u96fb\u8166\u88dc\u7fd2\u8ab2\u7a0b\u5427!<\/figcaption><\/figure>\r\n<\/br>Find A Teacher Form:\r\n<\/br>https:\/\/docs.google.com\/forms\/d\/1vREBnX5n262umf4wU5U2pyTwvk9O-JrAgblA-wH9GFQ\/viewform?edit_requested=true#responses\r\n<\/br><\/br>Email:\r\n<\/br>public1989two@gmail.com






\r\nwww.itsec.hk<\/a>
\r\nwww.itsec.vip<\/a>
\r\nwww.itseceu.uk<\/a>
<\/p>","protected":false},"excerpt":{"rendered":"
Learn all about the Spring @ConditionalOnProperty annotation.<\/p>\n
The post The Spring @ConditionalOnProperty Annotation<\/a> first appeared on Baeldung<\/a>.<\/p>\n
<\/a> <\/a> <\/a> <\/a> <\/a> <\/a> <\/a> <\/a> <\/div>\n<\/div>","protected":false},"author":792,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"slim_seo":{"title":"The Spring @ConditionalOnProperty Annotation - ITTeacherITFreelance.hk","description":"Learn all about the Spring @ConditionalOnProperty annotation. The post The Spring @ConditionalOnProperty Annotation first appeared on Baeldung .     &"},"footnotes":""},"categories":[6],"tags":[],"_links":{"self":[{"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/posts\/65358"}],"collection":[{"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/users\/792"}],"replies":[{"embeddable":true,"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/comments?post=65358"}],"version-history":[{"count":9,"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/posts\/65358\/revisions"}],"predecessor-version":[{"id":69165,"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/posts\/65358\/revisions\/69165"}],"wp:attachment":[{"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/media?parent=65358"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/categories?post=65358"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/itteacheritfreelance.hk\/wordpress\/index.php\/wp-json\/wp\/v2\/tags?post=65358"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}