├─application.properties
│   >> username=huan
├─application-dev.properties
│   >> username=huan.fu

ConfigurableEnvironment

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.6.6</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.huan.springcloud</groupId>
    <artifactId>springboot-extension-point</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>springboot-extension-point</name>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
    </dependencies>
</project>

vim application.properties

username=huan

SpringBoot版本
		>= 2.4 可以參考上圖中的使用 DeferredLogFactory 來輸出日志
		< 2.4
			1、參考如下鏈接 https://stackoverflow.com/questions/42839798/how-to-log-errors-in-a-environmentpostprocessor-execution
			2、核心代碼：
				@Component
				public class MyEnvironmentPostProcessor implements
				        EnvironmentPostProcessor, ApplicationListener<ApplicationEvent> {
				    private static final DeferredLog log = new DeferredLog();
				    @Override
				    public void postProcessEnvironment(
				            ConfigurableEnvironment env, SpringApplication app) {
				        log.error("This should be printed");
				    }
				    @Override
				    public void onApplicationEvent(ApplicationEvent event) {
				        log.replayTo(MyEnvironmentPostProcessor.class);
				    }
				}

org.springframework.boot.env.EnvironmentPostProcessor=\
  com.huan.springcloud.extensionpoint.environmentpostprocessor.CustomEnvironmentPostProcessor

@Component
public class PrintCustomizeEnvironmentProperty implements ApplicationRunner {

    private static final Logger log = LoggerFactory.getLogger(PrintCustomizeEnvironmentProperty.class);
    @Value("${username}")
    private String userName;
    @Override
    public void run(ApplicationArguments args) {
        log.info("獲取到的 username 的屬性值為: {}", userName);
    }
}

org.springframework.boot.context.logging.LoggingApplicationListener