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
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。
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。
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);
}
}
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);
}
}
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");
}
}
SpringApplicationEvent:获取 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);
}
}
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);
}
}
}
}
@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);
}
}
来源: http://blog.csdn.net/qq_30739519/article/details/78830773