Scheduling Recurring Tasks In Java Applications
By Tom White
2004-01-23
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Introduction
All manner of Java applications commonly need to schedule tasks for repeated execution. Enterprise applications need to schedule daily logging or overnight batch processes. A J2SE or J2ME calendar application needs to schedule alarms for a user's appointments. However, the standard scheduling classes, Timer and TimerTask, are not flexible enough to support the range of scheduling tasks typically required. In this article, Java developer Tom White shows you how to build a simple, general scheduling framework for task execution conforming to an arbitrarily complex schedule.
The java.util.Timer and java.util.TimerTask classes, which I'll refer to collectively as the Java timer framework, make it easy for programmers to schedule simple tasks. (Note that these classes are also available in J2ME.) Before this framework was introduced in the Java 2 SDK, Standard Edition, Version 1.3, developers had to write their own scheduler, which involved grappling with threads and the intricacies of the Object.wait() method. However, the Java timer framework is not rich enough to meet the scheduling requirements of many applications. Even a task that needs repeating every day at the same time cannot be directly scheduled using Timer, due to the time jumps that occur as daylight saving time comes and goes.
This article presents a scheduling framework that is a generalisation of Timer and TimerTask to allow more flexible scheduling. The framework is very simple -- it consists of two classes and an interface -- and it's easy to learn. If you're used to working with the Java timer framework, you should be able to pick up the scheduling framework very quickly. (For more information about the Java timer framework, see Resources.)
First published by IBM developerWorks
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