Mastering Spring Boot Configuration Properties

Spring Boot simplifies Java enterprise development by providing convention-over-configuration. A core part of this is its powerful configuration properties system, allowing you to externalize settings and manage your application's behavior without modifying code. This module dives deep into how to leverage these properties effectively.

What are Configuration Properties?

Configuration properties are key-value pairs that control your Spring Boot application's behavior. They can be used to configure data sources, server ports, logging levels, external service endpoints, and much more. Spring Boot automatically binds these properties to your Java objects, making them easily accessible within your application.

Externalize application settings for flexibility and maintainability.

Configuration properties allow you to change application behavior (like database URLs or server ports) without recompiling your code. This is crucial for deploying applications in different environments (development, staging, production).

By externalizing configuration, you decouple application settings from the application code itself. This means you can easily modify settings for different deployment environments (e.g., a development database versus a production database) by simply changing configuration files or environment variables, rather than needing to rebuild and redeploy the entire application. This practice significantly enhances maintainability and agility.

Sources of Configuration Properties

Spring Boot can load properties from various sources, with a specific order of precedence. Understanding this order is key to managing overrides and ensuring the correct values are applied.

Source	Description	Precedence
Command line arguments	Properties passed directly when running the application (e.g., `--server.port=9090`).	Highest
Java System Properties	System properties set via `-D` flag (e.g., `-Dserver.port=9090`).	High
OS Environment variables	Environment variables set in the operating system.	Medium-High
Application properties files	Files like `application.properties` or `application.yml` in the classpath.	Medium
Profile-specific properties files	Files like `application-{profile}.properties` or `application-{profile}.yml`.	Medium-Low
Configuration Server	External configuration management system (e.g., Spring Cloud Config).	Low

Binding Properties to Java Objects

The most elegant way to use configuration properties is by binding them to Plain Old Java Objects (POJOs). This makes your configuration type-safe and easier to manage.

To bind properties, create a POJO class with fields that match the property names (using camelCase for Java fields and kebab-case or dot-notation for properties). Annotate the class with @ConfigurationProperties and the field with @Value or let Spring handle the binding automatically. Spring Boot's auto-configuration will detect and register this bean if it's scanned by your application context.

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Text-based content

Library pages focus on text content

What annotation is used to mark a POJO for binding with configuration properties?

@ConfigurationProperties

Using `application.properties` and `application.yml`

Spring Boot automatically searches for

code

application.properties

and

code

application.yml

in the classpath.

code

application.yml

(YAML) offers a more human-readable, hierarchical structure, which is often preferred for complex configurations.

YAML is a superset of JSON and uses indentation to define structure, making it excellent for nested configurations.

For example, to configure a custom data source, you might have:

code

application.properties

properties

my.datasource.url=jdbc:postgresql://localhost:5432/mydb
my.datasource.username=user
my.datasource.password=password

code

application.yml

yaml

my:
  datasource:
    url: jdbc:postgresql://localhost:5432/mydb
    username: user
    password: password

Profiles for Environment-Specific Configuration

Profiles allow you to define different configurations for different environments. You can activate a profile using the

code

spring.profiles.active

property.

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For instance, you can have

code

application-dev.properties

for development and

code

application-prod.properties

for production. If you set

code

spring.profiles.active=prod

, Spring Boot will load

code

application-prod.properties

(and

code

application.properties

if it exists).

How do you activate a specific Spring Boot profile?

By setting the spring.profiles.active property (e.g., in application.properties, environment variables, or command line).

Best Practices

Always use

code

@ConfigurationProperties

for type-safe configuration. Prefer YAML for its readability. Leverage profiles for environment-specific settings. Avoid hardcoding sensitive information like passwords; use environment variables or secrets management tools.

Learning Resources

Spring Boot Configuration Properties - Official Documentation(documentation)

The definitive guide to Spring Boot's configuration properties, covering sources, binding, and best practices.

Spring Boot YAML Configuration - Baeldung(blog)

A practical tutorial explaining how to use YAML files for Spring Boot configuration, including examples.

Spring Boot @ConfigurationProperties - Tutorial(tutorial)

Learn how to bind external configuration properties to Java POJOs using the @ConfigurationProperties annotation.

Spring Boot Profiles - Baeldung(blog)

Understand how to use Spring Profiles to manage different configurations for various environments.

Spring Boot Externalized Configuration - YouTube(video)

A video explanation of Spring Boot's externalized configuration, covering properties files and binding.

Understanding Spring Boot Configuration Order(video)

Visualizes and explains the precedence order of Spring Boot configuration sources.

Spring Boot Application Properties - Java Code Geeks(blog)

An article detailing the use of application.properties and common properties available in Spring Boot.

Spring Boot Configuration Properties Binding - Spring Guides(documentation)

A quick guide from Spring.io on how to bind configuration properties to your application.

What is Spring Boot? - Wikipedia(wikipedia)

Provides a general overview of Spring Boot, its purpose, and its key features, including configuration.

Java Configuration Properties - Spring Framework Documentation(documentation)

Details on property editors and type conversion within the broader Spring Framework, which underpins Spring Boot's capabilities.