一、背景
spring boot的定時任務非常簡單，只需要在啟動類中加上@EnableScheduling注解，然后在對應的方法上配置@Scheduled就可以了，系統會自動處理並按照Scheduled中的配置定時執行方法。
但是在啟動項目的時候，發生了很詭異的現象，有兩個TaskScheduler/ScheduledExecutorService的異常打印了出來。但是系統並沒有受影響，依然正常啟動，而且定時任務也是正常執行。
2018-09-29 15:54:05,187 DEBUG main org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor [//] Could not find default TaskScheduler bean
org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'org.springframework.scheduling.TaskScheduler' available
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveNamedBean(DefaultListableBeanFactory.java:996)
at org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor.resolveSchedulerBean(ScheduledAnnotationBeanPostProcessor.java:278)
at org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor.finishRegistration(ScheduledAnnotationBeanPostProcessor.java:221)
at org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor.onApplicationEvent(ScheduledAnnotationBeanPostProcessor.java:200)
at org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor.onApplicationEvent(ScheduledAnnotationBeanPostProcessor.java:94)
at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:167)
at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:139)
at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:383)
at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:337)
at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:882)
at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.finishRefresh(EmbeddedWebApplicationContext.java:144)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:545)
at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:122)
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:737)
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:370)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:314)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1162)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1151)
at com.cmft.RunApp.main(RunApp.java:34)
2018-09-29 15:54:05,190 DEBUG main org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor [//] Could not find default ScheduledExecutorService bean
org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'java.util.concurrent.ScheduledExecutorService' available
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveNamedBean(DefaultListableBeanFactory.java:996)
at org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor.resolveSchedulerBean(ScheduledAnnotationBeanPostProcessor.java:278)
at org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor.finishRegistration(ScheduledAnnotationBeanPostProcessor.java:241)
at org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor.onApplicationEvent(ScheduledAnnotationBeanPostProcessor.java:200)
at org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor.onApplicationEvent(ScheduledAnnotationBeanPostProcessor.java:94)
at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:167)
at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:139)
at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:383)
at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:337)
at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:882)
at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.finishRefresh(EmbeddedWebApplicationContext.java:144)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:545)
at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:122)
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:737)
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:370)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:314)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1162)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1151)
at com.cmft.RunApp.main(RunApp.java:34)
2018-09-29 15:54:05,190 INFO main org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor [//] No TaskScheduler/ScheduledExecutorService bean found for scheduled processing
二、分析
雖然沒有影響系統，但是有異常看着總歸很難受，於是嘗試去探究下這個異常的原因。
通過觀察我們這兩個異常是日志模塊打印出來的debug級別日志
2018-09-29 15:54:05,187 DEBUG main org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor [//] Could not find default TaskScheduler bean
2018-09-29 15:54:05,190 DEBUG main org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor [//] Could not find default ScheduledExecutorService bean
而且都是在ScheduledAnnotationBeanPostProcessor類中打印出來。看類的名字我們大概能猜到這是@Scheduled注解的處理類。
根據日志內容我們定位到這個問題是由finishRegistration()方法打印出來。
private void finishRegistration() {
if (this.scheduler != null) {
this.registrar.setScheduler(this.scheduler);
}
if (this.beanFactory instanceof ListableBeanFactory) {
Map<String, SchedulingConfigurer> configurers = ((ListableBeanFactory)this.beanFactory).getBeansOfType(SchedulingConfigurer.class);
Iterator var2 = configurers.values().iterator();
while(var2.hasNext()) {
SchedulingConfigurer configurer = (SchedulingConfigurer)var2.next();
configurer.configureTasks(this.registrar);
}
}
if (this.registrar.hasTasks() && this.registrar.getScheduler() == null) {
Assert.state(this.beanFactory != null, "BeanFactory must be set to find scheduler by type");
try {
this.registrar.setTaskScheduler((TaskScheduler)this.resolveSchedulerBean(TaskScheduler.class, false));
} catch (NoUniqueBeanDefinitionException var8) {
try {
this.registrar.setTaskScheduler((TaskScheduler)this.resolveSchedulerBean(TaskScheduler.class, true));
} catch (NoSuchBeanDefinitionException var7) {
if (this.logger.isInfoEnabled()) {
this.logger.info("More than one TaskScheduler bean exists within the context, and none is named 'taskScheduler'. Mark one of them as primary or name it 'taskScheduler' (possibly as an alias); or implement the SchedulingConfigurer interface and call ScheduledTaskRegistrar#setScheduler explicitly within the configureTasks() callback: " + var8.getBeanNamesFound());
}
}
} catch (NoSuchBeanDefinitionException var9) {
this.logger.debug("Could not find default TaskScheduler bean", var9);
try {
this.registrar.setScheduler(this.resolveSchedulerBean(ScheduledExecutorService.class, false));
} catch (NoUniqueBeanDefinitionException var5) {
try {
this.registrar.setScheduler(this.resolveSchedulerBean(ScheduledExecutorService.class, true));
} catch (NoSuchBeanDefinitionException var4) {
if (this.logger.isInfoEnabled()) {
this.logger.info("More than one ScheduledExecutorService bean exists within the context, and none is named 'taskScheduler'. Mark one of them as primary or name it 'taskScheduler' (possibly as an alias); or implement the SchedulingConfigurer interface and call ScheduledTaskRegistrar#setScheduler explicitly within the configureTasks() callback: " + var5.getBeanNamesFound());
}
}
} catch (NoSuchBeanDefinitionException var6) {
this.logger.debug("Could not find default ScheduledExecutorService bean", var6);
this.logger.info("No TaskScheduler/ScheduledExecutorService bean found for scheduled processing");
}
}
}
this.registrar.afterPropertiesSet();
}
看代碼我們會發現，spring會從先從注冊過的bean中找任務調度器TaskScheduler
this.registrar.setTaskScheduler((TaskScheduler)this.resolveSchedulerBean(TaskScheduler.class, false));
如果獲取不到會拋出異常，然后打印出來
this.logger.debug("Could not find default TaskScheduler bean", var9);
然后繼續尋找定時任務的執行類ScheduledExecutorService
this.registrar.setScheduler(this.resolveSchedulerBean(ScheduledExecutorService.class, false));
如果找不到，會繼續拋出異常並打印出來
catch (NoSuchBeanDefinitionException var6) {
this.logger.debug("Could not find default ScheduledExecutorService bean", var6);
this.logger.info("No TaskScheduler/ScheduledExecutorService bean found for scheduled processing");
}
如此，便看到開頭我們看到的兩個異常。
看后面代碼我們會發現，如果注冊的bean中找不到，會調用scheduleTasks()方法初始化TaskScheduler，所以這兩個異常並不會影響系統。可能spring 的開發者是想借此提醒開發人員要自己在系統中注冊要使用的bean,而不是依賴框架來默認初始化。
解決辦法
修改日志級別
第一種是眼不見為凈法，簡單粗暴地修改日志級別就好。
log4j.logger.org.springframework.scheduling = INFO
這樣debug級別的日志就不會被打印出來，只有最后的info級別日志才會被打印。
注冊TaskScheduler
既然提示的異常是注冊的bean中找不到TaskScheduler，那么我們就注冊TaskScheduler。
@Bean
public TaskScheduler scheduledExecutorService() {
ThreadPoolTaskScheduler scheduler = new ThreadPoolTaskScheduler();
scheduler.setPoolSize(8);
scheduler.setThreadNamePrefix("scheduled-thread-");
return scheduler;
}