Question

我添加了一个带有@Scheduled(fixedDelay = 0)注释的方法，并且在方法中我使用了一些存储库，在类中初始化：@Autowired private ContactRepository contactRepository;

关于存储库：public interface ContactRepository extends CrudRepository<Contact, String>

问题是我得到了例外：

java.lang.IllegalArgumentException: null
    at java.util.concurrent.ScheduledThreadPoolExecutor.scheduleWithFixedDelay(ScheduledThreadPoolExecutor.java:589) ~[na:1.8.0_151]
    at java.util.concurrent.Executors$DelegatedScheduledExecutorService.scheduleWithFixedDelay(Executors.java:738) ~[na:1.8.0_151]
    at org.springframework.scheduling.concurrent.ConcurrentTaskScheduler.scheduleWithFixedDelay(ConcurrentTaskScheduler.java:235) ~[spring-context-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.scheduling.config.ScheduledTaskRegistrar.scheduleFixedDelayTask(ScheduledTaskRegistrar.java:511) ~[spring-context-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.scheduling.config.ScheduledTaskRegistrar.scheduleFixedDelayTask(ScheduledTaskRegistrar.java:485) ~[spring-context-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.scheduling.config.ScheduledTaskRegistrar.scheduleTasks(ScheduledTaskRegistrar.java:362) ~[spring-context-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.scheduling.config.ScheduledTaskRegistrar.afterPropertiesSet(ScheduledTaskRegistrar.java:332) ~[spring-context-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor.finishRegistration(ScheduledAnnotationBeanPostProcessor.java:280) ~[spring-context-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor.onApplicationEvent(ScheduledAnnotationBeanPostProcessor.java:211) ~[spring-context-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.scheduling.annotation.ScheduledAnnotationBeanPostProcessor.onApplicationEvent(ScheduledAnnotationBeanPostProcessor.java:102) ~[spring-context-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:172) ~[spring-context-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:165) ~[spring-context-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:139) ~[spring-context-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:400) ~[spring-context-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:354) ~[spring-context-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:888) ~[spring-context-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.finishRefresh(ServletWebServerApplicationContext.java:161) ~[spring-boot-2.0.1.RELEASE.jar:2.0.1.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:553) ~[spring-context-5.0.5.RELEASE.jar:5.0.5.RELEASE]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:140) ~[spring-boot-2.0.1.RELEASE.jar:2.0.1.RELEASE]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:759) [spring-boot-2.0.1.RELEASE.jar:2.0.1.RELEASE]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:395) [spring-boot-2.0.1.RELEASE.jar:2.0.1.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:327) [spring-boot-2.0.1.RELEASE.jar:2.0.1.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1255) [spring-boot-2.0.1.RELEASE.jar:2.0.1.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1243) [spring-boot-2.0.1.RELEASE.jar:2.0.1.RELEASE]
    at com.user.app.Main.main(Main.java:17) [classes/:na]

更新

当我使用fixedDelay = 1（或更多）时，它可以工作。为什么呢？

Answer 1

根据Javadoc for ScheduledExecutorService.scheduleWithFixedDelay(Runnable, long, long, TimeUnit)，IllegalArgumentException发生period <= 0。因此，大概@Scheduled(fixedDelay = 0)会导致period 0导致此异常发生。

也许Scheduled方法不是你真正想要的？如果你想在启动后执行一个方法，这个问题可能会有所帮助：Execute method on startup in spring

Answer 2

fixedDelay是以毫秒为单位执行计划任务的频率的周期。您无法将其设置为0，因为它没有意义并且您有相应的IllegalArgumentexception

Answer 3

@Scheduler注释将调用委托给ScheduledThreadPoolExecutor，其中fixedDelay参数为long delay。

这是Oracle JDK方法的实现：

public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command,
                                                 long initialDelay,
                                                 long delay,
                                                 TimeUnit unit) {
    if (command == null || unit == null)
        throw new NullPointerException();
    if (delay <= 0L)
        throw new IllegalArgumentException();
    ScheduledFutureTask<Void> sft =
        new ScheduledFutureTask<Void>(command,
                                      null,
                                      triggerTime(initialDelay, unit),
                                      -unit.toNanos(delay),
                                      sequencer.getAndIncrement());
    RunnableScheduledFuture<Void> t = decorateTask(command, sft);
    sft.outerTask = t;
    delayedExecute(t);
    return t;
}

我们清楚地看到if (delay <= 0L) throw new IllegalArgumentException();

设置0有什么意义？这真是一个非法论点。你能每隔0秒做一些动作吗？不，它基本上意味着这些行动同时发生。你需要它们之间的最短时间。

然后public abstract long initialDelay将允许您在执行方法之前指定第一个延迟。

首次执行a之前延迟的毫秒数 fixedRate()或fixedDelay()任务。

示例：

@Scheduled(initialDelay = 1000, fixedDelay = 10000)

任务将在initialDelay（1s）之后第一次执行 - 并且将根据fixedDelay（每10s）继续执行。

@Scheduled方法无法使用存储库

3 个答案: