Using schedulers
Schedulers enable Java™ Platform, Enterprise Edition (Java EE) application tasks to run at a requested time. Schedulers also enable application developers to create their own stateless session Enterprise JavaBeans (EJB) components to receive event notifications during a task life cycle, allowing the plugging-in of custom logging utilities or workflow applications.
About this task
- Invoke a session bean method
- Send a Java Message Service (JMS) message to a queue or topic
Stateless session EJB components are also used to provide generic calendaring. Developers can either use the supplied calendar bean or create their own for their existing business calendars. For example, one of your business processes might involve invoicing for services. With the scheduler's use of stateless EJB components, you can schedule when periodic email distributions are to be sent to your customers who have received invoices. The scheduler service performs these tasks, repeating as necessary, according to the metadata for that task.
A scheduler is the mechanism by which the timer service for Enterprise Java Beans runs for persistent timers. You can configure the EJB timer service to use many of the features that schedulers provide. See the configuring a timer service information for more details. Non-persistent timers do not use the scheduler service, but they can use the work manager for the scheduler. Non-persistent timers use a work manager directly.
Schedulers | EJB timers |
---|---|
Run stateless session EJB components and sends JMS messages | Run all EJB types except for stateful session beans |
Persistent, transactional and highly available | Persistent, transactional and highly available |
Tasks guaranteed to run only once | Timers guaranteed to run only once, if the timer EJB uses a container-managed global transaction |
Run repeating tasks using any calculation rules | Run repeating tasks using a repeating interval defined in milliseconds |
Uses a modified fixed-delay time calculation to determine repeating intervals (next run time based on the start-time of the previous task) | Uses a fixed-rate time calculation to determine repeating intervals (time of the next task is based on the original scheduled time) |
Programmatic task monitoring capability with the use of the NotificationSink stateless session EJB component | No programmatic timer monitoring |
Stop late or time-sensitive tasks from running | Stop late or time-sensitive tasks from running (achieved through manual detection within the javax.ejb.TimedObject implementation) |
Manage any task lifecycle (find, suspend, resume, cancel and purge tasks programmatically and through Java Management Extensions (JMX)) | Find and cancel its timers programmatically. Administrators find and cancel timers using a command-line utility. |
Store a limited amount of text with the data, like a Name (arbitrary data stored externally) | Store arbitrary data with a timer |
This task demonstrates how to manage, develop and interoperate with schedulers and subsequent tasks.