1. Introduction:
In Spring Boot, the @ConditionalOn annotation is used to conditionally enable or disable the creation of a bean based on certain conditions. Combined with the @Bean annotation, it allows for dynamic bean creation depending on the runtime environment or configuration.
2. Basic @ConditionalOnProperty:
The @ConditionalOnProperty annotation is one of the most commonly used conditions. It checks whether a specific property is present in the application’s configuration.
Example:
In this example, the MyConditionalBean will only be created if the property myapp.feature.enabled is set to true in the application properties.
3. @ConditionalOnClass and @ConditionalOnMissingClass:
The @ConditionalOnClass annotation checks for the presence of a specified class in the classpath, while @ConditionalOnMissingClass checks if the specified class is not present.
Example:
In this example, the WebController bean will only be created if the DispatcherServlet class is present in the classpath.
4. Custom Conditions with @Conditional:
You can create custom conditions by implementing the Condition interface and using the @Conditional annotation.
Example:
In this example, MyCustomCondition is a custom condition class implementing the Condition interface. The MyCustomBean will only be created if the condition specified in MyCustomCondition is met.
5. Combining Conditions:
You can combine multiple conditions using logical operators (&&, ||, !) with the @Conditional annotations.
Example:
In this example, the CombinedBean will only be created if both the property condition and the class condition are satisfied.
6. Conclusion:
@ConditionalOn annotations provide a powerful mechanism for conditionally creating beans in a Spring Boot application. This allows you to customize the application context based on various conditions, making your application more flexible and adaptive to different environments.
For a comprehensive understanding of conditions and their usage, refer to the official Spring Boot documentation: @Conditional annotations.
Feel free to experiment with different conditions and explore more advanced features provided by Spring Boot for conditional bean creation!
