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This article will explain in detail the example analysis of Spring Boot startup events and listeners. The editor thinks it is very practical, so I share it with you for reference. I hope you can get something after reading this article.

Spring Boot start event sequence

1 、 ApplicationStartingEvent

This event is sent at the start of the Spring Boot application and before any processing (except for listeners and initializers registration).

2 、 ApplicationEnvironmentPreparedEvent

This event is sent before the Spring context (context) is created when it is known to use the Spring context (Environment) in the context.

3 、 ApplicationContextInitializedEvent

This event is sent when the Spring application context (ApplicationContext) is ready and the application initializer (ApplicationContextInitializers) has been called before the definition of the bean (bean definitions) is loaded.

4 、 ApplicationPreparedEvent

This event is sent before the Spring context (context) is refreshed and after the definition of the bean (bean definitions) is loaded.

5 、 ApplicationStartedEvent

This event is sent after the Spring context (context) is refreshed and before the application/ command-line runners is called.

6 、 AvailabilityChangeEvent

This event is sent immediately after the previous event, with a status of ReadinessState.CORRECT, indicating that the application is already active.

7 、 ApplicationReadyEvent

This event is sent after any application/ command-line runners call.

8 、 AvailabilityChangeEvent

This event is sent immediately after the previous event, with status: ReadinessState.ACCEPTING_TRAFFIC, indicating that the application is ready to receive the request.

9 、 ApplicationFailedEvent

This event is sent when the application starts an exception.

The list of events described above includes only SpringApplicationEvents events bound to SpringApplication, and in addition to these events, the following events are also sent after ApplicationPreparedEvent and before ApplicationStartedEvent:

WebServerInitializedEvent

This Web server initialization event is sent after WebServer starts, along with ServletWebServerInitializedEvent (ServletWeb server initialization event) and ReactiveWebServerInitializedEvent (responsive Web server initialization event).

ContextRefreshedEvent

This context refresh event is sent after the Spring application context (ApplicationContext) refresh.

Custom startup event listener

Now that we know the events in the startup process of Spring Boot, we can deal with something we want to do at each step, and we just need to customize a listener to listen for an event.

For example, in step 8 above, when the application is launched and ready to receive requests, we simply output a success ID.

1. Create a new listener

Import lombok.extern.slf4j.Slf4j; import org.springframework.boot.availability.AvailabilityChangeEvent; import org.springframework.boot.availability.ReadinessState; import org.springframework.context.ApplicationListener; / sources * * Source Wechat official account: Java Technology Stack * / @ Slf4j public class JavastackListener implements ApplicationListener {@ Override public void onApplicationEvent (AvailabilityChangeEvent event) {log.info ("listening event:" + event) If (ReadinessState.ACCEPTING_TRAFFIC = = event.getState ()) {log.info ("Application startup is complete, you can request …") ;}

Create a new custom listener that implements the ApplicationListener interface. Generic AvailabilityChangeEvent means only listening for AvailabilityChangeEvent events.

Since the event in step 8 has the same name as the event in step 6, we can distinguish which part of the event is based on the status of the event.

2. Register the listener

There are two ways to register a listener:

1. Automatically register in the META-INF/spring.factories file in the resource directory:

Org.springframework.context.ApplicationListener=\ cn.javastack.springboot.features.listener.JavastackListener

2. If you are listening for events after the creation of a Spring application context (ApplicationContext), you can directly use the @ Component annotation on the listener, otherwise you need to use the automatic registration of the first method, because the ApplicationContext has not been created and the Bean cannot be loaded.

3. Application startup

Let's take a look at the startup log:

You can see that the monitoring log of step 6 and step 8 is output at the same time, but only the startup completion log of step 8 is output, and the custom snooping implementation is successful.

This is the end of this article on "sample analysis of Spring Boot startup events and listeners". I hope the above content can be of some help to you, so that you can learn more knowledge. if you think the article is good, please share it for more people to see.

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