How do you read meta data before the actual job in Spring Batch - spring-batch

Question

I'm currently designing a Spring Batch application that reads from a table, transforms the data and then writes it to another table.
However, before I begin reading the source table, I need to collect some meta data for the application run (e.g. read the holiday calendar table to determine if it's a bank holiday or not). This meta data will not change anymore during runtime, so it needs to be read only once, at the very beginning of the application run.
How can this be achieved? Use a JobListener? Configure a separate Job for this and then pass the information to the "actual" job through an ExecutionContext? Configure a separate step that gets only executed once?

Answer 1

Configure a JobExecutionListener to get the information you need and store it on the Job's ExecutionContext.
You can create a Listener class that either extends JobExecutionListenerSupport to only override the beforeJob method or create a standalone Listener class with a beforeJob method annotated with #BeforeJob.
When configuring the job, just add an instance of your custom Listener class to your JobBuilder configuration before adding any steps.
#Bean
public Job myJob() {
return this.jobBuilderFactory.get("myJob")
.listener(new MyListener())
.start(step1())
.next(step2())
.next(step3())
.build();
}
Anything you add in your Job's ExecutionContext can then be injected into any other Processor/Reader/Writer/Step beans that are configured as long as they are annotated with either #JobScope or #StepScope:
#Bean
#JobScope
public ItemReader<MyItem> myItemReader(
#Value("#{jobExecutionContext['myDate']}") Date myDate) {
//...
}
Component classes work the same as well
#Component
#JobScope
static class MyProcessor implements ItemProcessor<ItemA, ItemB> {
private Date myDate;
public MyProcessor(
#Value("#{jobExecutionContext['myDate']}") Date myDate) {
this.myDate = myDate;
}
// ...
}