springboot源码分析16-spring boot监听器使用

摘要：spring boot提供了一系列的监听器，方便我们开发人员使用和扩展。本文咱们详细讲解一下spring boot中的监听器。
spring boot中支持的事件类型定在org.springframework.boot.context.event包中，目前支持的事件类型有如下6种：
ApplicationFailedEvent
ApplicationPreparedEvent
ApplicationReadyEvent
ApplicationStartedEvent（Springboot2.x版本已修改为ApplicationStartingEvent）
SpringApplicationEvent
ApplicationEnvironmentPreparedEvent

1.1. 监听器的使用

第一：首先定义一个自己使用的监听器类并实现ApplicationListener接口。第二：通过SpringApplication类中的addListeners方法将自定义的监听器注册进去。

1.1.1. ApplicationFailedEvent

ApplicationFailedEvent：该事件为spring boot启动失败时的操作。/**
* spring boot 启动的时候出现异常事件
* @author www.shareniu.com
*
*/
public class ShareniuApplicationFailedEventListener implements ApplicationListener<ApplicationFailedEvent> {
@Override
public void onApplicationEvent(ApplicationFailedEvent event) {
System.out.println("--------------:ShareniuApplicationFailedEventListener");
Throwable exception = event.getException();
System.out.println(exception);
}
}
可以通过ApplicationFailedEvent 获取Throwable实例对象获取异常信息并处理。

1.1.2. ApplicationPreparedEvent

ApplicationPreparedEvent：上下文准备事件。上下文context已经准备完毕 ，可以通过ApplicationPreparedEvent获取到ConfigurableApplicationContext实例对象。ConfigurableApplicationContext类继承ApplicationContext类，但需要注意这个时候spring容器中的bean还没有被完全的加载，因此如果通过ConfigurableApplicationContext获取bean会报错的。比如报错：
Exception in thread "main" java.lang.IllegalStateException: org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@69b0fd6f has not been refreshed yet
获取到上下文之后，可以将其注入到其他类中，毕竟ConfigurableApplicationContext为引用类型。
public class ShareniuApplicationPreparedEventListener implements ApplicationListener<ApplicationPreparedEvent> {
@Override
public void onApplicationEvent(ApplicationPreparedEvent event) {
System.out.println("###############"+"ShareniuApplicationPreparedEventListener");
ConfigurableApplicationContext applicationContext = event.getApplicationContext();
//如果执行下面代码则报错
//ShareniuDemo shareniuDemo = applicationContext.getBean(ShareniuDemo.class);
//System.out.println(shareniuDemo);
}
}

1.1.3. ApplicationReadyEvent

ApplicationReadyEvent：上下文已经准备ok。这个时候就可以通过ApplicationReadyEvent获取ConfigurableApplicationContext，然后通过ConfigurableApplicationContext 获取bean的信息。
public class ShareniuApplicationReadyEventListener implements ApplicationListener<ApplicationReadyEvent> {
@Override
public void onApplicationEvent(ApplicationReadyEvent event) {
System.out.println("--------------------:ShareniuApplicationReadyEventListener");
ConfigurableApplicationContext applicationContext = event.getApplicationContext();
    //ShareniuDemo可以根基自身情况进行测试
ShareniuDemo shareniuDemo = applicationContext.getBean(ShareniuDemo.class);
}
}

1.1.4. ApplicationStartedEvent

ApplicationStartedEvent：spring boot 启动监听类。该类在SpringBoot2.x版本中已经废弃，修改为了最新的类，类名是ApplicationStartingEvent。这个事件是第一个产生的。可以在SpringApplication启动之前做一些手脚，比如修改SpringApplication实例对象中的属性值。
public class ShareniuApplicationStartedEventListener  implements ApplicationListener<ApplicationStartedEvent>{
@Override
public void onApplicationEvent(ApplicationStartedEvent event) {
SpringApplication springApplication = event.getSpringApplication();
springApplication.setShowBanner(false);
System.out.println("##############################ShareniuApplicationStartedEventListener");
}
}

1.1.5. SpringApplicationEvent

SpringApplicationEvent：获取SpringApplicationpublic class ShareniuSpringApplicationEventListener implements ApplicationListener<SpringApplicationEvent> {
@Override
public void onApplicationEvent(SpringApplicationEvent event) {
System.out.println("-----------------------:ShareniuSpringApplicationEventListener");
SpringApplication springApplication = event.getSpringApplication();
System.out.println("###############"+springApplication);
}
}

1.1.6. ApplicationEnvironmentPreparedEvent

ApplicationEnvironmentPreparedEvent：环境事先准备，spring boot中的环境已经准备ok可以通过ApplicationEnvironmentPreparedEvent获取到SpringApplication、ConfigurableEnvironment等等信息， 可以通过ConfigurableEnvironment实例对象来修改以及获取默认的环境信息。
public class ShasreniuApplicationEnvironmentPreparedEventListener  implements ApplicationListener<ApplicationEnvironmentPreparedEvent>{
@Override
public void onApplicationEvent(ApplicationEnvironmentPreparedEvent event) {
System.out.println("###############"+"ShasreniuApplicationEnvironmentPreparedEventListener");
SpringApplication springApplication = event.getSpringApplication();
ConfigurableEnvironment environment = event.getEnvironment();
long timestamp = event.getTimestamp();
Object source = event.getSource();
System.out.println("########################"+springApplication);
System.out.println("########################"+environment);
System.out.println("########################"+timestamp);
System.out.println("########################"+source); MutablePropertySources propertySources = environment.getPropertySources();
if (propertySources!=null) {
Iterator<PropertySource<?>> iterator = propertySources.iterator();
while (iterator.hasNext()) {
PropertySource<?> propertySource = (PropertySource<?>) iterator.next(); System.out.println("##############:propertySource"+propertySource);
}
}
 }
}

1.2. 监听器注册

@RestController@SpringBootApplication()
public class Application {
@RequestMapping("/")
String index() {
return "xxxxxxxxxxxxx";
}
public static void main(String[] args) {
SpringApplication springApplication = new SpringApplication(Application.class);
springApplication.addListeners(new ShareniuApplicationStartedEventListener());
springApplication.addListeners(new ShasreniuApplicationEnvironmentPreparedEventListener());
springApplication.addListeners(new ShareniuApplicationPreparedEventListener());
springApplication.addListeners(new ShareniuApplicationFailedEventListener());
springApplication.addListeners(new ShareniuApplicationReadyEventListener());
springApplication.addListeners(new ShareniuSpringApplicationEventListener());
springApplication.run(args);
}
}
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