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68. Job Scheduler

SolarNode provides a ManagedJobScheduler service that can automatically execute jobs exported by plugins that have user-defined schedules.

The Job Scheduler uses the Task Scheduler

The Job Scheduler service uses the Task Scheduler internally, which means the number of jobs that can execute simultaneously will be limited by its thread pool configuration.

68.1 Managed Jobs

Any plugin simply needs to register a ManagedJob service for the Job Scheduler to automatically schedule and execute the job. The schedule is provided by the getSchedle() method, which can return a cron expression or a plain number representing a millisecond period.

The net.solarnetwork.node.job.SimpleManagedJob class implements ManagedJob and can be used in most situations. It delegates the actual work to a net.solarnetwork.node.job.JobService API, discussed in the next section.

68.2 Job Service

The ManagedJob API delegates the actual task work to a JobService API. The executeJobService() method will be invoked when the job executes.

68.3 Example Managed Job

Let's imagine you have a com.example.Job class that you would like to allow users to schedule. Your class would implement the JobService interface, and then you would provide a localized messages properties file and configure the service using OSGi Blueprint.

package com.example;

import java.util.Collections;
import java.util.List;
import net.solarnetwork.node.job.JobService;
import net.solarnetwork.node.service.support.BaseIdentifiable;
import net.solarnetwork.settings.SettingSpecifier;

/**
 * My super-duper job.
 */
public class Job exetnds BaseIdentifiable implements JobService {
    @Override
    public String getSettingUid() {
        return "com.example.job"; // (1)!
    }

    @Override
    public List<SettingSpecifier> getSettingSpecifiers() {
        return Collections.emptyList(); // (2)!
    }

    @Override
    public void executeJobService() throws Exception {
        // do great stuff here!
    }
}
  1. The setting UID will be configured in the Blueprint XML as well.
  2. The SimpleManagedJob class we'll configure in Blueprint XML will automatically add a schedule setting to configure the job schedule.
title = Super-duper Job
desc = This job does it all.

schedule.key = Schedule
schedule.desc = The schedule to execute the job at. \
    Can be either a number representing a frequency in <b>milliseconds</b> \
    or a <a href="{0}">cron expression</a>, for example <code>0 * * * * *</code>.

<service interface="net.solarnetwork.node.job.ManagedJob"><!-- (1)! -->
    <service-properties>
        <entry key="service.pid" value="com.example.job"/>
    </service-properties>
    <bean class="net.solarnetwork.node.job.SimpleManagedJob"><!-- (2)! -->
        <argument>
            <bean class="com.example.Job">
                <property name="uid" value="com.example.job"/><!-- (3)! -->
                <property name="messageSource">
                    <bean class="org.springframework.context.support.ResourceBundleMessageSource">
                        <property name="basenames" value="com.example.Job"/>
                    </bean>
                </property>
            </bean>
        </argument>
        <property name="schedule" value="0 * * * * *"/>
    </bean>
</service>
  1. This registers a ManagedJob service with the SolarNode runtime.
  2. The SimpleManagedJob class is a handy ManagedJob implementation. It adds a schedule setting to any settings returned by the JobService.
  3. The uid value should match the service.pid used earlier, which matches the value returned by the getSettingUid() method in the Job class.

When this plugin is deployed in SolarNode, the component will appear on the main Settings page and offer a configurable Schedule setting, like this:

Example job in Settings UI