Java 使用 Spring 任务命名空间安排任务运行一次
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Scheduling tasks to run once, using the Spring task namespace
提问by Karl Johansson
I'm setting up a scheduled tasks scheme in spring, using the task namespace.
我在 spring 中设置了一个计划任务方案，使用任务命名空间。
I want to schedule most tasks to fire according to a cron expression, and some to fire just once, a fixed delay after startup, and then never again (i.e. what setting repeatCountto 0on a SimpleTriggerBean would achieve).
我想根据cron表达式大多数的任务安排到火，有的在启动后只启动一次，一个固定的延迟，然后再也没有（即什么设置repeatCount，以0将实现在SimpleTriggerBean）。
Is it possible to achieve this within the task namespace, or do I need to revert to defining beans for my triggers?
是否可以在任务命名空间中实现这一点，或者我是否需要恢复为我的触发器定义 bean？
采纳答案by Sean Patrick Floyd
If you have a look at the Task namespace XSD, you'll see that there are only three different configuration types: fixed-delay, fixed-rateand cron.
如果您查看Task 命名空间 XSD，您将看到只有三种不同的配置类型：fixed-delay、fixed-rate和cron。
And if you look at the source of ScheduledTasksBeanDefinitionParser, you'll see that no more than one of these values are evaluated. Here is the relevant part:
如果您查看ScheduledTasksBeanDefinitionParser的源代码，您会发现评估的值不超过一个。这是相关部分：
String cronAttribute = taskElement.getAttribute("cron");
if (StringUtils.hasText(cronAttribute)) {
cronTaskMap.put(runnableBeanRef, cronAttribute);
}
else {
String fixedDelayAttribute = taskElement.getAttribute("fixed-delay");
if (StringUtils.hasText(fixedDelayAttribute)) {
fixedDelayTaskMap.put(runnableBeanRef, fixedDelayAttribute);
}
else {
String fixedRateAttribute = taskElement.getAttribute("fixed-rate");
if (!StringUtils.hasText(fixedRateAttribute)) {
parserContext.getReaderContext().error(
"One of 'cron', 'fixed-delay', or 'fixed-rate' is required",
taskElement);
// Continue with the possible next task element
continue;
}
fixedRateTaskMap.put(runnableBeanRef, fixedRateAttribute);
}
}
So there is no way to combine these attributes. In short: the namespace won't get you there.
所以没有办法组合这些属性。简而言之：命名空间不会让你到达那里。
回答by aruizca
My working example:
我的工作示例：
<bean id="whateverTriggerAtStartupTime" class="org.springframework.scheduling.quartz.SimpleTriggerBean">
<property name="jobDetail" ref="whateverJob"/>
<property name="repeatCount" value="0"/>
<property name="repeatInterval" value="10"/>
</bean>
回答by Jeremy Gehrs
This works and is way easier than the other answers.
这有效并且比其他答案更容易。
// Will fire the trigger 1 + repeatCount number of times, start delay is in milliseconds
simple name: 'mySimpleTrigger', startDelay: 5000, repeatCount: 0
回答by bacar
If you don't need an initial delay, you can make it run 'just once' on startup as follows:
如果您不需要初始延迟，则可以使其在启动时“仅运行一次”，如下所示：
<task:scheduled-tasks>
<!-- Long.MAX_VALUE ms = 3E8 years; will run on startup
and not run again for 3E8 years -->
<task:scheduled ref="myThing" method="doStuff"
fixed-rate="#{ T(java.lang.Long).MAX_VALUE }" />
</task:scheduled-tasks>
(Of course, if you think your code is going to run for longer than 3E8 years, you may need a different approach...)
（当然，如果您认为您的代码将运行超过3E8 年，您可能需要不同的方法......）
If you need an initial delay, you can configure it as follows (I'm testing with Spring 3.1.1) - this doesn't require any additional dependencies and you don't have to write your own trigger, but you do have to configure the PeriodicTriggerprovided by Spring:
如果您需要初始延迟，您可以按如下方式配置（我正在使用 Spring 3.1.1 进行测试） - 这不需要任何额外的依赖项，您不必编写自己的触发器，但您必须配置PeriodicTriggerSpring提供的：
<bean id="onstart" class="org.springframework.scheduling.support.PeriodicTrigger" >
<!-- Long.MAX_VALUE ms = 3E8 years; will run 5s after startup and
not run again for 3E8 years -->
<constructor-arg name="period" value="#{ T(java.lang.Long).MAX_VALUE }" />
<property name="initialDelay" value="5000" />
</bean>
<task:scheduled-tasks>
<task:scheduled ref="myThing" method="doStuff" trigger="onstart" />
</task:scheduled-tasks>
Spring 3.2 appears to support the "initial-delay" attribute directly, but I haven't tested this; I'd guess this works:
Spring 3.2 似乎直接支持“initial-delay”属性，但我还没有测试过；我猜这有效：
<task:scheduled-tasks>
<task:scheduled ref="myThing" method="doStuff"
fixed-rate="#{ T(java.lang.Long).MAX_VALUE }"
initial-delay="5000"/>
</task:scheduled-tasks>
