Scheduling tasks to run once, using the Spring task namespace

Question

I'm setting up a scheduled tasks scheme in spring, using the task namespace.

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 (ie what setting repeatCount to 0 on a SimpleTriggerBean would achieve).

Is it possible to achieve this within the task namespace, or do I need to revert to defining beans for my triggers?

Answer 1

If you don't need an initial delay, you can make it run 'just once' on startup as follows:

<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...)

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 PeriodicTrigger provided by Spring:

<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:

<task:scheduled-tasks>
    <task:scheduled ref="myThing" method="doStuff" 
                        fixed-rate="#{ T(java.lang.Long).MAX_VALUE }" 
                        initial-delay="5000"/>
</task:scheduled-tasks>

Answer 2

My working example:

<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>

Answer 3

If you have a look at the Task namespace XSD , you'll see that there are only three different configuration types: fixed-delay , fixed-rate and 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:

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.

Answer 4

This works and is way easier than the other answers.

    // Will fire the trigger 1 + repeatCount number of times, start delay is in milliseconds
    simple name: 'mySimpleTrigger', startDelay: 5000, repeatCount: 0