Spring Boot embedded Tomcat不在ApplicationListener中加载外部属性文件

import org.springframework.boot.context.event.ApplicationStartedEvent;
import org.springframework.context.ApplicationListener;
import org.springframework.core.env.ConfigurableEnvironment;
import org.springframework.core.env.PropertiesPropertySource;
import org.springframework.core.io.support.PropertiesLoaderUtils;

import java.io.IOException;
import java.util.Properties;

public class ExternalPropertiesListener implements ApplicationListener<ApplicationStartedEvent> {

    @Override
    public void onApplicationEvent(ApplicationStartedEvent event) {
        ConfigurableEnvironment environment = event.getApplicationContext().getEnvironment();
        try {
            Properties externalProperties = PropertiesLoaderUtils.loadProperties("external.properties");
            PropertiesPropertySource propertySource = new PropertiesPropertySource("externalProperties", externalProperties);
            environment.getPropertySources().addLast(propertySource);
        } catch (IOException e) {
            // 处理加载外部属性文件失败的情况
        }
    }
}

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.context.annotation.Bean;

@EnableAutoConfiguration
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

    @Bean
    public ExternalPropertiesListener externalPropertiesListener() {
        return new ExternalPropertiesListener();
    }
}