How are configuration properties bound in Spring Boot?

Configuration properties in Spring Boot can be bound to configuration property classes from property sources, including application properties files, environment variables, and command line parameters. Property binding is done through the @ConfigurationProperties annotation. Practical case: Create a configuration attribute class, bind the attribute source, and obtain the configuration attribute.

Binding of configuration properties in Spring Boot

Spring Boot provides a powerful configuration property mechanism, which allows us to Easily bind configuration values ​​to our applications from various sources such as application properties files, environment variables, and command line arguments.

Creation of configuration attribute class

First, we need to create a configuration attribute class to declare the fields and types of the configuration attribute. For example, the following class defines two configuration properties:

@ConfigurationProperties("my.app")
public class AppConfig {
    private String name;
    private int port;

    // getter and setter methods
}

Property Sources

In Spring Boot, configuration properties can be bound from various property sources. The most common property sources include:

• Application properties file: Located in src/main/resources/application.properties, contains key-value pairs.
• Environment variables: System environment variables, named in the format of MY_APP_NAME etc.
• Command line parameters: Pass to the application in the format of --my.app.name=value etc.

Property binding

Spring Boot automatically binds configuration properties from the property source to the configuration property class. This binding is done through the @ConfigurationProperties annotation.

Practical Case

The following is a practical case showing how to use configuration properties in a Spring Boot application:

@SpringBootApplication
public class MyApp {
    public static void main(String[] args) {
        SpringApplication.run(MyApp.class, args);
        AppConfig config = beanFactory.getBean(AppConfig.class);

        System.out.println("Name: " + config.getName());
        System.out.println("Port: " + config.getPort());
    }
}

In this example , we create a AppConfig class and declare it as a configuration property class using the @ConfigurationProperties annotation. Then, we use beanFactory to get the AppConfig bean and print the configured property values.

Run this application and provide the application.properties file:

my.app.name=My Application
my.app.port=8080

You should see the output in the console:

Name: My Application
Port: 8080

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