摘要：spring boot提供了一系列的監聽器，方便我們開發人員使用和擴充套件。

本文咱們詳細講解一下spring boot中的監聽器。

spring boot中支援的事件型別定在org.springframework.boot.context.event包中，目前支援的事件型別有如下6種：

ApplicationFailedEvent

ApplicationPreparedEvent

ApplicationReadyEvent

ApplicationStartedEvent（Springboot2.x版本已修改為ApplicationStartingEvent）

SpringApplicationEvent

ApplicationEnvironmentPreparedEvent

1.1. 監聽器的使用

第一：首先定義一個自己使用的監聽器類並實現ApplicationListener介面。

第二：通過SpringApplication類中的addListeners方法將自定義的監聽器註冊進去。

1.1.1. ApplicationFailedEvent

ApplicationFailedEvent：該事件為spring boot啟動失敗時的操作。

/**

* spring boot 啟動的時候出現異常事件

* @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);

}

}

可以通過ApplicationFailedEvent 獲取Throwable例項物件獲取異常資訊並處理。

1.1.2. ApplicationPreparedEvent

ApplicationPreparedEvent：上下文準備事件。

上下文context已經準備完畢 ，可以通過ApplicationPreparedEvent獲取到ConfigurableApplicationContext例項物件。ConfigurableApplicationContext類繼承ApplicationContext類，但需要注意這個時候spring容器中的bean還沒有被完全的載入，因此如果通過ConfigurableApplicationContext獲取bean會報錯的。比如報錯：

Exception in thread "main" java.lang.IllegalStateException: org.springframework.boot[email protected]69b0fd6f has not been refreshed yet

獲取到上下文之後，可以將其注入到其他類中，畢竟ConfigurableApplicationContext為引用型別。

public class ShareniuApplicationPreparedEventListener implements ApplicationListener<ApplicationPreparedEvent> {

@Override

public void onApplicationEvent(ApplicationPreparedEvent event) {

System.out.println("###############"+"ShareniuApplicationPreparedEventListener");

ConfigurableApplicationContext applicationContext = event.getApplicationContext();

//如果執行下面程式碼則報錯

//ShareniuDemo shareniuDemo = applicationContext.getBean(ShareniuDemo.class);

//System.out.println(shareniuDemo);

}

}

1.1.3. ApplicationReadyEvent

ApplicationReadyEvent：上下文已經準備ok。

這個時候就可以通過ApplicationReadyEvent獲取ConfigurableApplicationContext，然後通過ConfigurableApplicationContext 獲取bean的資訊。

public class ShareniuApplicationReadyEventListener implements ApplicationListener<ApplicationReadyEvent> {

@Override

public void onApplicationEvent(ApplicationReadyEvent event) {

System.out.println("--------------------:ShareniuApplicationReadyEventListener");

ConfigurableApplicationContext applicationContext = event.getApplicationContext();

    //ShareniuDemo可以根基自身情況進行測試

ShareniuDemo shareniuDemo = applicationContext.getBean(ShareniuDemo.class);

}

}

1.1.4. ApplicationStartedEvent

ApplicationStartedEvent：spring boot 啟動監聽類。該類在SpringBoot2.x版本中已經廢棄，修改為了最新的類，類名是ApplicationStartingEvent。這個事件是第一個產生的。

可以在SpringApplication啟動之前做一些手腳，比如修改SpringApplication例項物件中的屬性值。

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：獲取SpringApplication

public 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：環境事先準備，spring boot中的環境已經準備ok

可以通過ApplicationEnvironmentPreparedEvent獲取到SpringApplication、ConfigurableEnvironment等等資訊， 可以通過ConfigurableEnvironment例項物件來修改以及獲取預設的環境資訊。

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. 監聽器註冊

@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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