Dynamically setting FlatFileItemReader.resource

[JWindebank]

Hi everyone, I have pretty much solved my external mapping issue however have one additional problem to solve for.

I would like to be able to modify the resource property of FlatFileItemReader at runtime with a value sourced earlier in the job.

I have the current job:

<job id="processTrades">
	<step id="step1" next="step2">
		<tasklet ref="mappingLoaderTasklet" />
	</step>
	<step id="step2">
		<tasklet>
			<chunk reader="tradeReader" processor="tradeProcessor" writer="tradeWriter" commit-interval="1" />
		</tasklet>
	</step>
</job>

mappingLoaderTasklet is used to load a static class with some mapping details from an external configuration file that can be used throughout the job.

package com.windebank.projects.tradeloader;

import org.apache.log4j.Logger;
import org.springframework.batch.core.StepContribution;
import org.springframework.batch.core.scope.context.ChunkContext;
import org.springframework.batch.core.step.tasklet.Tasklet;
import org.springframework.batch.repeat.RepeatStatus;

public class MappingLoaderTasklet implements Tasklet {

	final Logger logger = Logger.getLogger(MappingLoaderTasklet.class);
	
	private String inputFile;

	public String getInputFile() {
		return inputFile;
	}

	public void setInputFile(String inputFile) {
		this.inputFile = inputFile;
	}

	public RepeatStatus execute(StepContribution contribution,
			ChunkContext chunkContext) throws Exception {

		TradeMapping.inputFile = inputFile;
		TradeMapping.read();
		
		logger.info("MappingLoaderTasklet: " + inputFile);

		return null;
	}
}

One of these mapping fields is the input file location that I want used by the ItemReader. I would like to be able to effectively do the following:

FlatFileItemReader.resource = TradeMapping.fileName

I just don't know how this can work when interacting with the beans. I know I can use late binding from the JobParameters as follows:

<beans:bean name="tradeReader"
	class="org.springframework.batch.item.file.FlatFileItemReader" scope="step">
	<beans:property name="lineMapper" ref="tradeLineMapper" />
	<beans:property name="resource" value="#{jobParameters['inputFile']}" />
</beans:bean>

However this still isn't late enough binding for what I want.

Anyone got any ideas please?

[Marten Deinum]

If you don't expose the inputFile as job parameter it will not be available. You only set it inside your tasklet and not as a job parameter, hence your binding isn't working. You can store the attribute/add it to the execution context and retrieve it from there. If my memory serves me well there is either a sample doing that or it is written out in the Spring Batch Reference Guide.

Also storing attributes in a class with static members isn't a very good idea IMHO (what happens if you have 2 instances of the job running, what about restartability ?!). But that is just IMHO ofcourse .

[JWindebank]

Thanks Marten. I am only using the static members for now to solve the problem of not being able to pass objects around, however the execution context appears to solve this. Thank you!

I have one additional question I'm hoping someone can help with please. If I look at how to implement functionality to save an object to the execution context, it requires me to modify the ItemReader. Eg:

public class SavingItemWriter implements ItemWriter<Object> {
    private StepExecution stepExecution;

    public void write(List<? extends Object> items) throws Exception {
        // ...

        ExecutionContext stepContext = this.stepExecution.getExecutionContext();
        stepContext.put("someKey", someObject);
    }

    @BeforeStep
    public void saveStepExecution(StepExecution stepExecution) {
        this.stepExecution = stepExecution;
    }
}

This looks fine except my program is using the built in FlatFileItemReader and so I have nowhere to add the code as required. I am trying to get my head around this and it looks like I might need a delegate, or to extend the FlatFileItemReader. Am I on the right path here please? If so, can anyone provide any tips or references for me as the Spring Batch Reference is a little light on info around these.

Thanks again.