Solving @ ConditionalOnProperty Injection Issues in Spring Boot

Learn how to handle issues with `@ ConditionalOnProperty` in Spring Boot and ensure proper bean management with practical solutions.
---

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Parameter 0 of constructor when using @ ConditionalOnProperty

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding the @ ConditionalOnProperty Injection Problem

When developing applications using Spring Boot, you might encounter situations where certain services should only be available under specific conditions. One common approach for managing this behavior is utilizing the @ ConditionalOnProperty annotation. However, it can lead to complications, especially when dealing with dependency injection. In this guide, we'll explore a specific issue regarding the injection of AmazonSimpleEmailService into an email service, and how to effectively resolve it.

The Problem Statement

Imagine you're working on a Send Email Service that integrates with AWS Simple Email Service (SES). You've set up a configuration class where you want to conditionally enable the AmazonSimpleEmailService based on a property value. Here’s a simplified version of your setup:

[[See Video to Reveal this Text or Code Snippet]]

[[See Video to Reveal this Text or Code Snippet]]

You might wonder, "How can I prevent this error without registering the bean when it's not needed?" Let's explore some effective strategies to tackle this issue.

Solutions to the Injection Problem

Option 1: Making @ Autowired Optional

One straightforward approach is to use the @ Autowired annotation's required attribute, which you can set to false:

[[See Video to Reveal this Text or Code Snippet]]

By making the dependency optional, Spring won't throw an error if the bean isn't found when aws-active is set to false. However, be aware that you will need to handle the potential null case in your EmailService logic.

Option 2: Making Your Service Conditional

Another elegant solution involves making your EmailService class conditional as well. You can leverage the @ ConditionalOnProperty annotation similar to how you did it for the AmazonSimpleEmailService:

[[See Video to Reveal this Text or Code Snippet]]

This way, EmailService will only be created when the property is true, eliminating the injection error altogether.

Option 3: Leveraging Inheritance with Interfaces

For a more scalable solution, especially when you have multiple implementations, you can adopt an inheritance approach. Define a common interface for your service and implement different behaviors based on conditions:

[[See Video to Reveal this Text or Code Snippet]]

Using this approach allows you to have various implementations of a service based on the specified conditions, while ensuring that there's always a bean available for injection, thus preventing errors.

Conclusion

Managing conditional beans in Spring Boot can pose challenges, especially when it comes to dependency injection. By implementing one of the solutions outlined above, you can effectively handle the absence of required beans without encountering errors. Whether you opt to make beans optional, apply conditions to your services, or utilize inheritance, ensuring maintainable and robust code should always be the goal.

You've learned how to overcome these challenges and can confidently implement @ ConditionalOnProperty in your own applications. Happy coding!