What are @ConditionalOnClass and @ConditionalOnMissingClass annotations in Spring Boot?
In Spring Boot, conditional annotations allow you to configure your application based on the presence or absence of specific classes in the classpath. Two of these annotations are @ConditionalOnClass and ConditionalOnMissingClass. Let’s discuss each of these in detail.
@ConditionalOnClass
@ConditionalOnClass is an annotation used to conditionally enable or disable a configuration class based on the presence of specific classes in the classpath. It’s commonly used in auto-configuration classes to ensure that certain configurations are only created when the required dependencies/classess are available.
Usage
@Configuration
@ConditionalOnClass(ExampleDependency.class)
public class ExampleAutoConfiguration {
// ...
}
In the example above, the ExampleAutoConfiguration class will only be loaded if the ExampleDependency class is found.
@ConditionalOnMissingClass
@ConditionalOnMissingClass, as the name suggests, is the opposite of @ConditionalOnClass. It enables a configuration or method when a specific class is not present. This is useful in scenarios where you want to provide a default or fallback configuration if certain dependencies are missing.
@Configuration
@ConditionalOnMissingClass("com.example.ExampleDependency")
public class FallbackConfiguration {
//...
}
In the example above, the FallbackConfiguration class will only be loaded if the com.example.ExampleDependency class is not present or found in the classpath.
Conclusion
@ConditionalOnClass and @ConditionalOnMissingClass are useful annotations that help you create flexible Spring Boot applications. They allow you to conditionally enable or disable configurations based on the presence or absence of specific classes on the classpath, leading to more adaptable code.