Introduction

It is possible to achieve conditional bean loading based on both property values and complex expressions in Spring Boot. While the @ConditionalOnProperty and @ConditionalOnExpression annotations are not repeatable on the same element, you can combine their functionality.

Combining @ConditionalOnProperty and @ConditionalOnExpression:

The most common approach to combine these conditions is to use a single @ConditionalOnExpression annotation that incorporates both property checks and more complex expressions using Spring Expression Language (SpEL).

For example, to check for the presence and value of a property while also evaluating a more complex condition:

@Configuration
@ConditionalOnExpression("${my.feature.enabled:false} && T(java.time.LocalDate).now().getDayOfWeek().getValue() == 5")
public class MyConditionalConfiguration {
    // ... bean definitions ...
}

In this example:

• ${my.feature.enabled:false} checks the value of the my.feature.enabled property, defaulting to false if not present.
• T(java.time.LocalDate).now().getDayOfWeek().getValue() == 5 is a SpEL expression that checks if the current day of the week is Friday (where 5 represents Friday).
• The && operator ensures both conditions must be true for the configuration to be loaded.

Alternative using @Conditional and custom Condition implementations:

For more complex or reusable conditional logic, you can implement the org.springframework.context.annotation.Condition interface and use it with the general @Conditional annotation. This allows you to encapsulate detailed logic for property checks, expression evaluations, or any other custom conditions within a dedicated class.

public class MyCustomCondition implements Condition {
    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        // Implement complex logic here, combining property checks and expressions
        boolean propertyEnabled = context.getEnvironment().getProperty("my.feature.enabled", Boolean.class, false);
        boolean isFriday = java.time.LocalDate.now().getDayOfWeek().getValue() == 5;
        return propertyEnabled && isFriday;
    }
}

@Configuration
@Conditional(MyCustomCondition.class)
public class MyConditionalConfiguration {
    // ... bean definitions ...
}

This approach provides greater flexibility and maintainability for intricate conditional requirements.

Conclusion

Spring's conditional annotations, including @ConditionalOnProperty, @ConditionalOnExpression, and the more general @Conditional, provide powerful mechanisms for dynamically managing the application context and load beans depending on your most complex use cases.