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

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?

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To be able to use the jobParameters I think you need to define your reader as scope 'step', but I am not sure if you can do it using annotations.

Using xml-config it would go like this:

<bean id="foo-readers" scope="step"
class="...MyReader">
<property name="fileName" value="#{jobExecutionContext['fileName']}" />
</bean>

See further at the Spring Batch documentation.

Perhaps it works by using @Scope and defining the step scope in your xml-config:

<bean class="org.springframework.batch.core.scope.StepScope" />
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Did you declare the jobparameters as map properly as bean?

Or did you perhaps accidently instantiate a JobParameters object, which has no getter for the filename?

For more on expression language you can find information in Spring documentation here.

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最佳答案

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" />
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Pretty late, but you can also do this by annotating a @BeforeStep method:

@BeforeStep
public void beforeStep(final StepExecution stepExecution) {
JobParameters parameters = stepExecution.getJobExecution().getJobParameters();
//use your parameters
}
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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

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While executing the job we need to pass Job parameters as follows:

JobParameters jobParameters= new JobParametersBuilder().addString("file.name", "filename.txt").toJobParameters();
JobExecution execution = jobLauncher.run(job, jobParameters);

by using the expression language we can import the value as follows:

 #{jobParameters['file.name']}
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Complement with an additional example, you can access all job parameters in JavaConfig class:

@Bean
@StepScope
public ItemStreamReader<GenericMessage> reader(@Value("#{jobParameters}") Map<String,Object> jobParameters){
....
}
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This could be an easier manner to do it:

@Configuration
@Setter
@StepScope
public  class Reader extends FlatFileItemReader<Object> {


public Reader(@Value("#{jobParameters['filePath']}") String resource){
setResource(new FileSystemResource(resource));
}


}
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You can use StepExecution context inside a method annotated with @BeforeStep annotation inside your item reader to get the Job parameters & set it to a variable, which you can use inside your read method.

In my case I've written something like this :-

@Component
@RequiredArgsConstructor
public class SpelItemReader implements ItemReader<BatchRequest>{


private String requestId;




@Override
public BatchRequest read() {
//access the request-id variable here
}


@BeforeStep
public void beforeStep(StepExecution stepExecution) {
requestId = stepExecution.getJobParameters().getString("requestId");
}

}


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