Resolving the Issue of @Value Annotation Not Assigning Values in Spring Boot 2.7.5

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Troubleshooting the @Value Annotation in Spring Boot 2.7.5

The Problem: @Value Annotation Not Assigning Values

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Common Checks Performed

The developer conducted extensive troubleshooting, verifying the following:

Inclusion of @Configuration annotation at the top of the class where @Value is used

Proper key-value assignment and spelling of all keys in the properties

No issues with library imports

Correct import statement for @Value annotation

Proper configuration of the resources folder as a 'Resources Root'

Despite these checks, the issue persisted, leading to an exploration of further possible misconfigurations.

The Solution: Understanding How Spring Boot Loads Properties

After investigating the situation, it was discovered that the primary issue stemmed from calling the configuration class that includes the @Value annotation from the main() method of the @SpringBootApplication. This led to the conclusion that properties are not available until the Spring application context is fully initialized and running. Therefore, manually attempting to access properties in main() will result in a null assignment.

Alternative Approach for Loading Properties

To effectively load properties before the Spring application is fully running, one recommended approach is using a Properties object, as shown below:

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

This snippet ensures that your properties are accessible before the Spring context is fully set up, mitigating the risk of receiving null values.

Conclusion

If you encounter the issue with the @Value annotation returning null in Spring Boot, remember that property binding only occurs once the Spring context is up and running. By adjusting your approach to load properties ahead of the Spring application lifecycle, you can overcome this stumbling block.

Key Takeaways:

Check where and how properties are loaded in relation to the application lifecycle.

Using a dedicated Properties instance to ensure access to values prior to application startup can be a temporary solution.

Take care to structure your configuration classes for optimal property management within Spring.

Final Note

Understanding the Spring application context and lifecycle is crucial when dealing with annotations like @Value. A thorough approach will not only help you address current issues but also equip you to handle future challenges more effectively.