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Learn how to effectively read dynamic values from application.yml in Java Spring using the @ Value annotation or @ ConfigurationProperties. Get practical examples and code snippets.
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How to Read Values from application.yml in Java Spring with Variable Names

When working with Java Spring applications, you may encounter situations where you need to read values from your application.yml configuration file. One common scenario is when you want to retrieve a value using a variable name, making your code flexible and reusable. In this guide, we'll explore how to achieve this with practical examples.

The Problem: Dynamic Value Retrieval

Suppose you have an application.yml file with a structure like this:

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You want to access the values of mla and mlb using a variable called site. However, the traditional use of the @ Value annotation in Spring Boot does not directly support dynamic variable names, leading to the following code snippet that falls short:

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Here, the placeholder %s is meant to be replaced with the value of the site variable, but Spring does not interpret this as intended.

The Solution: Using a Map

If you're keen on staying with the @ Value annotation, one effective approach is to convert your site data into a map format in your application.yml. You can structure your application.yml like this:

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Step-by-Step Implementation

Modify application.yml: Replace the previous site structure with a string representation of a map:

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Define the Map in Your Code: Use the @ Value annotation to inject the map into a Map<String, Integer> type variable:

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Accessing Values: Now, in your controller or service class, you can retrieve values by the variable name:

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Alternative Solution: Using @ ConfigurationProperties

Another approach is to utilize @ ConfigurationProperties, which provides a more structured way to map configuration properties to your Spring beans. Here's how to implement it:

Define the Structure in application.yml:

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Create a Configuration Class:

Create a class to hold your configuration data:

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Register Your Properties Class:

Ensure you can access your properties class in Spring by using the @ EnableConfigurationProperties annotation:

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Accessing Values in Your Controller or Service:

You can now inject UserIdProperties wherever needed:

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Conclusion

In summary, reading values from application.yml using a variable name in Java Spring can be approached in a couple of ways. Whether you choose to utilize the @ Value annotation with a map or leverage @ ConfigurationProperties for a more structured solution, both methods can help you manage your configuration properties efficiently.

Feel free to implement these solutions to enhance the flexibility and dynamism of your Spring applications! Happy coding!