[springboot]事件监听(三)

前言
spring boot在启动过程中增加事件监听机制，为用户功能拓展提供极大的便利。
支持的事件类型四种
ApplicationStartedEvent
ApplicationEnvironmentPreparedEvent
ApplicationPreparedEvent
ApplicationFailedEvent
实现监听步骤：
1.监听类实现ApplicationListener接口
2.将监听类添加到SpringApplication实例
ApplicationStartedEvent
ApplicationStartedEvent：spring boot启动开始时执行的事件
public class MyApplicationStartedEventListener implements ApplicationListener {
private Logger logger = LoggerFactory.getLogger(MyApplicationStartedEventListener.class);

@Override
public void onApplicationEvent(ApplicationStartedEvent applicationStartedEvent) {

    logger.info("开始启动了");
}

}
ApplicationEnvironmentPreparedEvent
ApplicationEnvironmentPreparedEvent：spring boot 对应Enviroment已经准备完毕，但此时上下文context还没有创建。
public class MyApplicationEnvironmentPreparedEventListener implements ApplicationListener {
Logger logger = LoggerFactory.getLogger(MyApplicationEnvironmentPreparedEventListener.class);
@Override
public void onApplicationEvent(ApplicationEnvironmentPreparedEvent applicationEnvironmentPreparedEvent) {
ConfigurableEnvironment environment = applicationEnvironmentPreparedEvent.getEnvironment();
MutablePropertySources propertySources = environment.getPropertySources();
Iterator