Mapping YAML to Configuration classes in Spring Boot

Tags: spring boot java

Written by: Tushar Sharma

Spring Boot provides an elegant way to bind YAML configurations directly to Java classes using the @ConfigurationProperties annotation. This tutorial will walk you through the basics and show you how to map a nested YAML structure to a configuration class.

Prerequisites

1. Spring Boot project: If you don't have a project ready, you can create one using Spring Initializr.

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YAML Example

Consider the following YAML structure:

In this YAML:

• access.projects is a list of project configurations.
• Each project has allowedAccess (a string) and allowedGroup (a list of strings).

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Step 1: Adding Dependencies

Ensure you have the following dependency in your pom.xml (if using Maven):

This dependency generates metadata for configuration properties, making it easier to manage properties in the IDE.

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Step 2: Define the Configuration Class

To bind the YAML structure, create a configuration class using the @ConfigurationProperties annotation.

Explanation:

1. @ConfigurationProperties("access"): Maps properties under the access key in the YAML file.
2. Nested Class Project: Represents the structure of each project entry in the projects list.
3. Lombok Annotations:
   • @Getter and @Setter reduce boilerplate code for getters and setters.
   • Ensure Lombok is configured in your project.

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Step 3: Enable Configuration Properties

Annotate your main application class with @EnableConfigurationProperties to enable configuration property binding.

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Step 4: Using the Configuration in Your Application

You can now inject and use the configuration in any Spring component.

Example Usage:

Output:

For the provided YAML, the output will be:

Allowed Access: t1
Allowed Groups: [m1, m2]
Allowed Access: t2
Allowed Groups: [m2, m3]

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Key Benefits

1. Type Safety: Configuration values are bound directly to strongly typed Java objects.
2. Centralized Configuration: Manage all project-specific configurations in one place.
3. Flexibility: Easy to extend or modify as the YAML structure changes.

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Common Pitfalls

1. Ensure YAML indentation is correct: Misaligned spaces can cause parsing errors.
2. Dependency management: Ensure the spring-boot-configuration-processor is included for better development experience.
3. Lombok setup: Verify Lombok is properly configured in your IDE.

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Conclusion

Using @ConfigurationProperties in Spring Boot is a powerful way to manage hierarchical configurations. By following this tutorial, you can effectively bind YAML properties to Java classes and use them in your application. Happy coding!

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References:

• Spring Boot Documentation

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