Spring Boot Application Properties

The Spring Boot, application properties play a crucial role in configuring your application. These properties are typically defined in property files (e.g., application.properties or application.yml) and control various aspects of your Spring Boot application, such as database connections, server port, logging levels, and more. Here’s a breakdown of how Spring Boot application properties work:

1. Property Files:

Spring Boot applications commonly use property files to store configuration properties. These files can be in either of the following formats:

• application.properties: A plain text file with properties in a key=value format, one per line.
• application.yml: A YAML file that uses a hierarchical, human-readable format to define properties.

You can place these property files in your project’s src/main/resources directory, and Spring Boot will automatically load them.

2. Property Sources:

Spring Boot combines properties from various sources to create the application’s configuration. The order of precedence for property sources, from highest to lowest, is as follows:

• Command-line arguments: Properties provided as command-line arguments take the highest precedence. For example, --server.port=8081 would set the server port to 8081.
• Properties files: The application.properties and application.yml files are the default property sources. Additional property files can be loaded using the spring.config.name and spring.config.location properties.
• Environment-specific properties: Spring Boot allows you to define environment-specific property files (e.g., application-dev.properties) to override or extend properties for specific profiles.
• System properties: Properties set as system properties (e.g., using -Dproperty.name=value).
• Environment variables: Properties defined as environment variables.
• Application properties: Properties defined directly in your Spring Boot application using @Value annotations, Environment beans, or other means.
• Default properties: Spring Boot provides many default properties for various configurations. These act as fallback values if no other source provides a property.

3. Property Names:

Property names can be hierarchical and are typically separated by periods (e.g., server.port, spring.datasource.url). The property names are case-sensitive. You can access these properties in your application code using @Value annotations, Spring’s Environment API, or by using the @ConfigurationProperties annotation.

4. Profiles:

Spring Boot supports profiles, which allow you to define different sets of properties for different runtime environments (e.g., development, testing, production). Profiles are often specified in property files with names like application-dev.properties or application-prod.yml. You can activate a specific profile using the spring.profiles.active property.

5. Custom Property Files:

In addition to the default application.properties and application.yml files, you can specify custom property files using the spring.config.name and spring.config.location properties. For example, to use a custom property file named myapp.properties located in a specific directory:

java -jar myapp.jar --spring.config.name=myapp --spring.config.location=file:/path/to/properties/

6. Property Encryption:

Spring Boot provides mechanisms for encrypting sensitive property values, such as database passwords, using tools like Jasypt or custom encryption providers.

7. Documentation:

Spring Boot’s Actuator module provides a convenient way to document and expose application properties, their descriptions, and current values via endpoints like /actuator/configprops. This is useful for inspecting application properties at runtime.

By using Spring Boot application properties, you can easily configure and customize your application without modifying code, making your application more flexible and maintainable across different environments.