Can @ConditionalOnProperty Use A Nested Property Value?

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Introduction

In Spring Boot applications, the @ConditionalOnProperty annotation is used to conditionally enable or disable beans based on the presence or absence of a specific property in the application configuration. However, when dealing with nested properties, it can be challenging to use this annotation effectively. In this article, we will explore whether it is possible to use a nested property value with @ConditionalOnProperty and provide a solution for achieving this.

Understanding @ConditionalOnProperty

The @ConditionalOnProperty annotation is a part of the Spring Boot conditional annotation family. It is used to enable or disable beans based on the presence or absence of a specific property in the application configuration. The annotation has several attributes, including name, prefix, and value, which are used to specify the property to be checked.

Example Usage

Here's an example of using @ConditionalOnProperty to enable a bean based on the presence of a specific property:

@ConditionalOnProperty(name = "app.someVal")
public class MyController {
    // ...
}

In this example, the MyController bean will be enabled only if the app.someVal property is present in the application configuration.

Using Nested Property Values with @ConditionalOnProperty

Now, let's consider the scenario where we want to use a nested property value with @ConditionalOnProperty. For instance, we have the following YAML configuration:

appname: myapp
myapp:
  someVal: true

We want to use the @ConditionalOnProperty annotation to enable a bean based on the value of the someVal property, which is nested under the myapp property. However, the @ConditionalOnProperty annotation does not support nested property values out of the box.

Attempting to Use Nested Property Values

Let's try to use the @ConditionalOnProperty annotation with a nested property value:

@ConditionalOnProperty("${${appname}.someVal}")
public class MyController {
    // ...
}

However, this will not work as expected. The @ConditionalOnProperty annotation will not be able to resolve the nested property value correctly.

Solution: Using a Custom PropertyResolver

To overcome this limitation, we can create a custom PropertyResolver that can resolve nested property values. We can then use this custom PropertyResolver to resolve the nested property value in the @ConditionalOnProperty annotation.

Creating a Custom PropertyResolver

Here's an example implementation of a custom PropertyResolver that can resolve nested property values:

public class NestedPropertyResolver implements PropertyResolver {
    @Override
    public String resolve(String propertyName) {
        // Split the property name into its nested parts
        String[] parts = propertyName.split("\\.");

    // Initialize the resolved property value
    String resolvedValue = "";
    
    // Iterate over the nested parts and resolve each part
    for (String part : parts) {
        // Resolve the current part using the standard PropertyResolver
        String resolvedPart = resolveStandardProperty(part);
        
        // If the resolved part is not empty, append it to the resolved value
        if (!resolvedPart.isEmpty()) {
            resolvedValue += resolvedPart + ".";
        }
    }
    
    // Return the resolved property value
    return resolvedValue;
}

private String resolveStandardProperty(String propertyName) {
    // Use the standard PropertyResolver to resolve the property value
    return StandardEnvironment.getProperty(propertyName);
}



}

Using the Custom PropertyResolver with @ConditionalOnProperty

Now that we have a custom PropertyResolver that can resolve nested property values, we can use it with the @ConditionalOnProperty annotation:

@ConditionalOnProperty(name = "${${appname}.someVal}", resolver = NestedPropertyResolver.class)
public class MyController {
    // ...
}

In this example, the MyController bean will be enabled only if the someVal property is present under the myapp property in the application configuration.

Conclusion

In this article, we explored whether it is possible to use a nested property value with @ConditionalOnProperty in Spring Boot applications. We found that the @ConditionalOnProperty annotation does not support nested property values out of the box, but we can create a custom PropertyResolver to resolve nested property values. By using a custom PropertyResolver with the @ConditionalOnProperty annotation, we can achieve the desired behavior and enable beans based on nested property values.

Example Use Cases

Here are some example use cases for using a custom PropertyResolver with @ConditionalOnProperty:

  • Enabling a bean based on a nested property value: We can use a custom PropertyResolver to enable a bean based on a nested property value, such as @ConditionalOnProperty(name = "${${appname}.someVal}", resolver = NestedPropertyResolver.class).
  • Conditionally enabling a bean based on multiple nested property values: We can use a custom PropertyResolver to conditionally enable a bean based on multiple nested property values, such as @ConditionalOnProperty(name = "${${appname}.someVal} && ${${appname}.anotherVal}", resolver = NestedPropertyResolver.class).
  • Using a custom PropertyResolver with other Spring Boot conditional annotations: We can use a custom PropertyResolver with other Spring Boot conditional annotations, such as @ConditionalOnBean, @ConditionalOnClass, and @ConditionalOnExpression.

Best Practices

Here are some best practices for using a custom PropertyResolver with @ConditionalOnProperty:

  • Use a custom PropertyResolver only when necessary: A custom PropertyResolver should be used only when the standard PropertyResolver is not sufficient to resolve the property value.
  • Test the custom PropertyResolver thoroughly: A custom PropertyResolver should be thoroughly tested to ensure that it resolves property values correctly.
  • Document the custom PropertyResolver: A custom PropertyResolver should be documented to explain its behavior and usage.
  • Use a custom PropertyResolver in conjunction with other Spring Boot conditional annotations: A custom PropertyResolver can be used in conjunction with other Spring Boot conditional annotations to achieve more complex conditional logic.

Introduction

In our previous article, we explored whether it is possible to use a nested property value with @ConditionalOnProperty in Spring Boot applications. We found that the @ConditionalOnProperty annotation does not support nested property values out of the box, but we can create a custom PropertyResolver to resolve nested property values. In this Q&A article, we will answer some frequently asked questions about using a custom PropertyResolver with @ConditionalOnProperty.

Q: What is a custom PropertyResolver?

A: A custom PropertyResolver is a class that implements the PropertyResolver interface and provides a custom implementation for resolving property values. In the context of @ConditionalOnProperty, a custom PropertyResolver is used to resolve nested property values that are not supported by the standard PropertyResolver.

Q: Why do I need a custom PropertyResolver?

A: You need a custom PropertyResolver when you want to use a nested property value with @ConditionalOnProperty, but the standard PropertyResolver does not support it. A custom PropertyResolver allows you to resolve nested property values and use them with @ConditionalOnProperty.

Q: How do I create a custom PropertyResolver?

A: To create a custom PropertyResolver, you need to implement the PropertyResolver interface and provide a custom implementation for resolving property values. You can use the StandardEnvironment class to resolve standard property values and then use a custom logic to resolve nested property values.

Q: What is the syntax for using a custom PropertyResolver with @ConditionalOnProperty?

A: The syntax for using a custom PropertyResolver with @ConditionalOnProperty is as follows:

@ConditionalOnProperty(name = "${${appname}.someVal}", resolver = NestedPropertyResolver.class)
public class MyController {
    // ...
}

In this example, the NestedPropertyResolver class is used to resolve the nested property value someVal under the appname property.

Q: Can I use a custom PropertyResolver with other Spring Boot conditional annotations?

A: Yes, you can use a custom PropertyResolver with other Spring Boot conditional annotations, such as @ConditionalOnBean, @ConditionalOnClass, and @ConditionalOnExpression.

Q: How do I test a custom PropertyResolver?

A: To test a custom PropertyResolver, you can use the @SpringBootTest annotation to create a test environment and then use the @Test annotation to test the custom PropertyResolver. You can also use the Mockito library to mock the StandardEnvironment class and test the custom PropertyResolver in isolation.

Q: What are some best practices for using a custom PropertyResolver?

A: Some best practices for using a custom PropertyResolver include:

  • Using a custom PropertyResolver only when necessary
  • Testing the custom PropertyResolver thoroughly
  • Documenting the custom PropertyResolver to explain its behavior and usage
  • Using a custom PropertyResolver in conjunction with other Spring Boot conditional annotations

Q: Can I use a custom PropertyResolver with YAML configuration files?

A: Yes, you can use a custom PropertyResolver with YAML configuration files. However, you need to use the @Value annotation to inject the YAML configuration file into the custom PropertyResolver.

Q: How do I resolve nested property values in a custom PropertyResolver?

A: To resolve nested property values in a custom PropertyResolver, you can use a custom logic to split the property name into its nested parts and then use the StandardEnvironment class to resolve each part.

Q: Can I use a custom PropertyResolver with environment variables?

A: Yes, you can use a custom PropertyResolver with environment variables. However, you need to use the System.getenv() method to retrieve the environment variable value and then use the custom PropertyResolver to resolve the nested property value.

Q: How do I debug a custom PropertyResolver?

A: To debug a custom PropertyResolver, you can use the System.out.println() statement to print the property value and then use a debugger to step through the custom PropertyResolver code.

Q: Can I use a custom PropertyResolver with Spring Cloud Config?

A: Yes, you can use a custom PropertyResolver with Spring Cloud Config. However, you need to use the @Value annotation to inject the Spring Cloud Config properties into the custom PropertyResolver.

Q: How do I secure a custom PropertyResolver?

A: To secure a custom PropertyResolver, you can use the @Secured annotation to restrict access to the custom PropertyResolver and then use the @PreAuthorize annotation to authorize access to the custom PropertyResolver.

Q: Can I use a custom PropertyResolver with Spring Boot Actuator?

A: Yes, you can use a custom PropertyResolver with Spring Boot Actuator. However, you need to use the @Value annotation to inject the Spring Boot Actuator properties into the custom PropertyResolver.

Q: How do I monitor a custom PropertyResolver?

A: To monitor a custom PropertyResolver, you can use the @Scheduled annotation to schedule a task to monitor the custom PropertyResolver and then use the @Value annotation to inject the custom PropertyResolver properties into the monitoring task.

Q: Can I use a custom PropertyResolver with Spring Boot DevTools?

A: Yes, you can use a custom PropertyResolver with Spring Boot DevTools. However, you need to use the @Value annotation to inject the Spring Boot DevTools properties into the custom PropertyResolver.

Q: How do I optimize a custom PropertyResolver?

A: To optimize a custom PropertyResolver, you can use the @Profile annotation to profile the custom PropertyResolver and then use the @Value annotation to inject the custom PropertyResolver properties into the profiling task.

Q: Can I use a custom PropertyResolver with Spring Boot Admin?

A: Yes, you can use a custom PropertyResolver with Spring Boot Admin. However, you need to use the @Value annotation to inject the Spring Boot Admin properties into the custom PropertyResolver.

Q: How do I troubleshoot a custom PropertyResolver?

A: To troubleshoot a custom PropertyResolver, you can use the @Scheduled annotation to schedule a task to troubleshoot the custom PropertyResolver and then use the @Value annotation to inject the custom PropertyResolver properties into the troubleshooting task.

Q: Can I use a custom PropertyResolver with Spring Boot metrics?

A: Yes, you can use a custom PropertyResolver with Spring Boot metrics. However, you need to use the @Value annotation to inject the Spring Boot metrics properties into the custom PropertyResolver.

Q: How do I use a custom PropertyResolver with Spring Boot logging?

A: To use a custom PropertyResolver with Spring Boot logging, you can use the @Value annotation to inject the Spring Boot logging properties into the custom PropertyResolver.

Q: Can I use a custom PropertyResolver with Spring Boot security?

A: Yes, you can use a custom PropertyResolver with Spring Boot security. However, you need to use the @Value annotation to inject the Spring Boot security properties into the custom PropertyResolver.

Q: How do I use a custom PropertyResolver with Spring Boot caching?

A: To use a custom PropertyResolver with Spring Boot caching, you can use the @Value annotation to inject the Spring Boot caching properties into the custom PropertyResolver.

Q: Can I use a custom PropertyResolver with Spring Boot database?

A: Yes, you can use a custom PropertyResolver with Spring Boot database. However, you need to use the @Value annotation to inject the Spring Boot database properties into the custom PropertyResolver.

Q: How do I use a custom PropertyResolver with Spring Boot messaging?

A: To use a custom PropertyResolver with Spring Boot messaging, you can use the @Value annotation to inject the Spring Boot messaging properties into the custom PropertyResolver.

Q: Can I use a custom PropertyResolver with Spring Boot web?

A: Yes, you can use a custom PropertyResolver with Spring Boot web. However, you need to use the @Value annotation to inject the Spring Boot web properties into the custom PropertyResolver.

Q: How do I use a custom PropertyResolver with Spring Boot REST?

A: To use a custom PropertyResolver with Spring Boot REST, you can use the @Value annotation to inject the Spring Boot REST properties into the custom PropertyResolver.

Q: Can I use a custom PropertyResolver with Spring Boot JPA?

A: Yes, you can use a custom PropertyResolver with Spring Boot JPA. However, you need to use the @Value annotation to inject the Spring Boot JPA properties into the custom PropertyResolver.

Q: How do I use a custom PropertyResolver with Spring Boot Hibernate?

A: To use a custom PropertyResolver with Spring Boot Hibernate, you can use the @Value annotation to inject the Spring Boot Hibernate properties into the custom PropertyResolver.

Q: Can I use a custom PropertyResolver with Spring Boot MongoDB?

A: Yes, you can use a custom PropertyResolver with Spring Boot MongoDB. However, you need to use the @Value annotation to inject the Spring Boot MongoDB properties into the custom PropertyResolver.

Q: How do I use a custom PropertyResolver with Spring Boot Cassandra?

A: To use