In Spring Boot, @ConfigurationProperties is a convenient way to bind properties defined in your application configuration files (such as application.properties or application.yml) to Java objects. This tutorial will guide you through using @ConfigurationProperties with examples to externalize and manage configuration properties in a Spring Boot application.
Prerequisites
Ensure you have the following set up:
- A Spring Boot project (you can use the Spring Initializer to generate one).
- An integrated development environment (IDE) of your choice.
Step 1: Add Dependencies
Make sure your pom.xml (if using Maven) or build.gradle (if using Gradle) includes the necessary dependencies for Spring Boot configuration properties.
Maven:
Step 2: Create a Configuration Properties Class
Create a Java class that will serve as the configuration properties holder. This class should have fields corresponding to the properties you want to configure.
In this example, we’re using the @Component annotation to make sure that the AppProperties class is a Spring bean and can be injected into other components.
Step 3: Define Properties in application.properties
Now, define the properties you want to configure in your application.properties file. Prefix these properties with the value specified in @ConfigurationProperties(prefix = "app").
Step 4: Use Configuration Properties in Your Application
Inject the AppProperties bean into your components where you need access to the configured properties.
Step 5: Run Your Application
Run your Spring Boot application and navigate to http://localhost:8080/info. You should see the application information retrieved from the AppProperties configuration properties.
Additional Configuration Options
Nested Configuration Properties
You can use nested classes to organize your configuration properties:
In application.properties:
Relaxing Binding Rules
By default, the binding is strict, and any property not found in the configuration properties class will result in a BindingException. You can relax these rules with ignoreUnknownFields and ignoreInvalidFields:
With these settings, unknown fields will throw an exception, but invalid fields will be silently ignored.
Conclusion
Using @ConfigurationProperties in Spring Boot is an efficient way to externalize configuration and manage properties in your application. It promotes a clean separation of configuration concerns and provides a more structured and type-safe approach to dealing with configuration parameters. This tutorial covered the basic steps to get you started, but there are many more advanced features and customization options available depending on your specific needs.
