This post is part of a series delving into the details of the JSR-352 (Java Batch) specification. Each post examines a very specific part of the specification and looks at how it works and how you might use it in a real batch application.To start at the beginning, follow the link to the first post.The next post in the series is
here.
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The restart method on the JobOperator interface allows you to provide a Properties object containing restart parameters. This is equivalent to the Properties object of job parameters that can be supplied when a job is started for the first time.
The batch specification says that job parameters are NOT remembered from one execution to the next. That means that if you specified parameters when you started the job the first time, you need to decide if you want to specify those same (or different) parameters when you restart the job when it fails (or, to be optimistic, if it fails).
Whether you specify different values for the parameters on a restart than you did when you initially started the job depends, of course, on what those parameters do in the JSL. The parameters might point to files that need to be processed and you still need to process those same files.
On the other hand, it could be that the job failed because of a problem with some of those files and you have new, corrected, files somewhere else and the job restart needs to point there instead.
There is one thing you cannot change across a restart. If you have a partitioned step and coded the partition plan right in the JSL (meaning no PartitionMapper is involved), then the number of partitions must be the same. If the value used for the number of partitions comes from a job parameter, then you have to specify the same value on the restart as you did on the initial start of the job.
This post is shorter than most of them because this topic is really pretty simple and straight forward. I feel a bit guilty. Maybe I will just make it look longer and see if anybody notices. Obviously our song is “Killing Time” by Triumph.
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And that about wraps it up for this topic.