自定义Listener

前言

为什么要自定义Listener？

通过自定义，可以在程序启动过程中监听特定事件，再回调处理逻辑。

自定义SpringApplicationRunListener

1、创建自定义SpringApplicationRunListener，在回调方法中实现自定义的处理逻辑

public class CustomSpringRunListener implements SpringApplicationRunListener {
    public CustomSpringRunListener(SpringApplication application, String[] args) {
        System.out.println("CustomSpringRunListener constructor");
    }

    public void starting() {

    }

    public void environmentPrepared(ConfigurableEnvironment environment) {

    }

    public void contextPrepared(ConfigurableApplicationContext context) {

    }

    public void contextLoaded(ConfigurableApplicationContext context) {

    }

    public void started(ConfigurableApplicationContext context) {

    }

    public void running(ConfigurableApplicationContext context) {

    }

    public void failed(ConfigurableApplicationContext context, Throwable exception) {

    }
}

2、在META/spring.factories中声明自定义Listener

org.springframework.boot.SpringApplicationRunListener=\
  edu.xjh.test.listener.CustomSpringRunListener

从而，SpringBoot启动过程中会扫描META/spring.factories，加载所有的SpringApplicationRunListener

自定义ApplicationListener

1、自定义ApplicationListener，实现onApplicationEvent逻辑

public class CustomApplicationListener implements ApplicationListener<ApplicationEvent> {
    public void onApplicationEvent(ApplicationEvent event) {
		// 判断事件类型，执行特定处理逻辑
        if (event instanceof ApplicationStartingEvent) {
            System.out.println("CustomApplicationListener catch ApplicationStartingEvent");
        }else if (event instanceof ApplicationEnvironmentPreparedEvent) {
            System.out.println("CustomApplicationListener catch ApplicationEnvironmentPreparedEvent");
        }
    }
}

2、声明ApplicationListener

方法1：

在META/spring.factories中声明自定义ApplicationListener，因为启动过程中会扫描该文件进行加载

org.springframework.context.ApplicationListener=\
  edu.xjh.test.listener.CustomApplicationListener

方法2：

在实例化SpringApplication之后，手动添加Listener

public static void main(String[] args) {
	SpringApplication application = new SpringApplication(DemoApp.class);
	application.addListeners(new CustomApplicationListener());
	application.run(args);
}