Скачать или смотреть How to Use YML Values Inside @ Pattern Annotations in Java

Learn how to externalize regex patterns into your YML files and utilize them within `@ Pattern` annotations in Java. Discover a custom solution that allows dynamic regex validation in your Spring applications.
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This video is based on the question https://stackoverflow.com/q/64450291/ asked by the user 'Jacob Kurian' ( https://stackoverflow.com/u/6880125/ ) and on the answer https://stackoverflow.com/a/64453329/ provided by the user 'jokarls' ( https://stackoverflow.com/u/6909026/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Use YML Values Inside @ Pattern Annotations in Java

In modern Java applications, especially those built with Spring, there's often a need to keep configurations clean and externalized. One potential use case is wanting to move regex patterns defined in Java annotations to an external configuration file, like a YML file. A common requirement is to replace hardcoded values in the @ Pattern annotation with dynamic values fetched from configurations. This guide will guide you through the process of achieving that for a simple regex pattern such as HELLO|WORLD stored in a YML file.

The Problem

You might find yourself in a situation where you want to use an externalized string value (like a regex pattern) in a Spring application. For instance, you have the following YML file:

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You want to use this value in the @ Pattern annotation within your Java class like this:

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However, the standard @ Pattern annotation does not support dynamic content directly, and you’ve already tried alternatives that did not yield the desired results.

Common Attempts That Didn't Work

Using Spring Expression Language (SpEL) in the @ Pattern annotation such as:

@ Pattern(regexp = "# {@ properties.getValidCallerValue()}")

@ Pattern(regexp = "${properties.getValidCallerValue()}")

Unfortunately, these methods aren't supported, which leads us to contemplate other solutions.

The Solution

While it might seem that direct usage isn't possible, we can create a custom solution by implementing our own validation annotation. Let’s break this down into manageable steps.

1. Create a Custom Annotation

We’ll create a new annotation called PropertyPattern. This annotation will take the name of the property you want to validate against:

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2. Implement the Validator

Next, we need a validator class that checks the value against the regex defined in the YML file. Below is how you can implement the validator:

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3. Use the Custom Annotation

Now, you can use the newly defined PropertyPattern annotation in your classes. Here’s an example of how you can use it:

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Conclusion

By creating a custom annotation combined with a validator, you can successfully fetch regex patterns from your YML configurations and utilize them for validation in your Spring application. This not only enhances the maintainability and clarity of your code but also makes your patterns manageable outside of the codebase.

Externalizing configurations is a best practice, and with the approach discussed here, you'll neatly decouple concerns in your application. Now you can dynamically adjust validation constraints without altering code every time a pattern needs changing.

Feel free to adapt this solution to your specific needs and explore how dynamic configurations could revolutionize your development workflow!