JAVA高级面试进阶训练营视频教程

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一、背景

spring boot的定时任务非常简单，只需要在启动类中加上@EnableScheduling注解，然后在对应的方法上配置@Scheduled就可以了，系统会自动处理并按照Scheduled中的配置定时执行方法。

但是在启动项目的时候，发生了很诡异的现象，有两个TaskScheduler/ScheduledExecutorService的异常打印了出来。但是系统并没有受影响，依然正常启动，而且定时任务也是正常执行。

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

虽然没有影响系统，但是有异常看着总归很难受，于是尝试去探究下这个异常的原因。

通过观察我们这两个异常是日志模块打印出来的debug级别日志

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类中打印出来。看类的名字我们大概能猜到这是@Scheduled注解的处理类。

根据日志内容我们定位到这个问题是由finishRegistration()方法打印出来。

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();
    }

看代码我们会发现，spring会从先从注册过的bean中找任务调度器TaskScheduler

 this.registrar.setTaskScheduler((TaskScheduler)this.resolveSchedulerBean(TaskScheduler.class, false));

如果获取不到会抛出异常，然后打印出来

this.logger.debug("Could not find default TaskScheduler bean", var9);

然后继续寻找定时任务的执行类ScheduledExecutorService

this.registrar.setScheduler(this.resolveSchedulerBean(ScheduledExecutorService.class, false));

如果找不到，会继续抛出异常并打印出来

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，便看到开头我们看到的两个异常。

看后面代码我们会发现，如果注册的bean中找不到，会调用scheduleTasks()方法初始化TaskScheduler，所以这两个异常并不会影响系统。可能spring 的开发者是想借此提醒开发人员要自己在系统中注册要使用的bean,而不是依赖框架来默认初始化。

解决办法

修改日志级别

第一种是眼不见为净法，简单粗暴地修改日志级别就好。

log4j.logger.org.springframework.scheduling = INFO

这样debug级别的日志就不会被打印出来，只有最后的info级别日志才会被打印。

注册TaskScheduler

既然提示的异常是注册的bean中找不到TaskScheduler，那么我们就注册TaskScheduler。

    @Bean
    public TaskScheduler scheduledExecutorService() {
        ThreadPoolTaskScheduler scheduler = new ThreadPoolTaskScheduler();
        scheduler.setPoolSize(8);
        scheduler.setThreadNamePrefix("scheduled-thread-");
        return scheduler;
    }

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