How to get access to job parameters from ItemReader, in Spring Batch?

Question

This is part of my job.xml:

<job id="foo" job-repository="job-repository">   <step id="bar">     <tasklet transaction-manager="transaction-manager">       <chunk commit-interval="1"         reader="foo-reader" writer="foo-writer"       />     </tasklet>   </step> </job> 

This is the item reader:

import org.springframework.batch.item.ItemReader; import org.springframework.beans.factory.annotation.Value; import org.springframework.stereotype.Component; @Component("foo-reader") public final class MyReader implements ItemReader<MyData> {   @Override   public MyData read() throws Exception {     //...   }   @Value("#{jobParameters['fileName']}")   public void setFileName(final String name) {     //...   } } 

This is what Spring Batch is saying in runtime:

Field or property 'jobParameters' cannot be found on object of  type 'org.springframework.beans.factory.config.BeanExpressionContext' 

What's wrong here? Where I can read more about these mechanisms in Spring 3.0?

Answer 1

As was stated, your reader needs to be 'step' scoped. You can accomplish this via the @Scope("step") annotation. It should work for you if you add that annotation to your reader, like the following:

import org.springframework.batch.item.ItemReader; import org.springframework.beans.factory.annotation.Value; import org.springframework.stereotype.Component;  @Component("foo-reader") @Scope("step") public final class MyReader implements ItemReader<MyData> {   @Override   public MyData read() throws Exception {     //...   }    @Value("#{jobParameters['fileName']}")   public void setFileName(final String name) {     //...   } } 

This scope is not available by default, but will be if you are using the batch XML namespace. If you are not, adding the following to your Spring configuration will make the scope available, per the Spring Batch documentation:

<bean class="org.springframework.batch.core.scope.StepScope" /> 

Answer 2

If you want to define your ItemReader instance and your Step instance in a single JavaConfig class. You can use the @StepScope and the @Value annotations such as:

@Configuration public class ContributionCardBatchConfiguration {     private static final String WILL_BE_INJECTED = null;     @Bean    @StepScope    public FlatFileItemReader<ContributionCard> contributionCardReader(@Value("#{jobParameters['fileName']}")String contributionCardCsvFileName){       ....    }     @Bean    Step ingestContributionCardStep(ItemReader<ContributionCard> reader){          return stepBuilderFactory.get("ingestContributionCardStep")                  .<ContributionCard, ContributionCard>chunk(1)                  .reader(contributionCardReader(WILL_BE_INJECTED))                  .writer(contributionCardWriter())                  .build();     } } 

The trick is to pass a null value to the itemReader since it will be injected through the @Value("#{jobParameters['fileName']}") annotation.

Thanks to Tobias Flohre for his article : Spring Batch 2.2 – JavaConfig Part 2: JobParameters, ExecutionContext and StepScope