FlatFileItemWriter - Writer must be open before it can be written to

I've a SpringBatch Job where I skip all duplicate items write to a Flat file.

However the FlatFileItemWriter throws the below error whenever there's a duplicate:

Writer must be open before it can be written to

Below is the Writer & SkipListener configuration -

    @Bean(name = "duplicateItemWriter")
    public FlatFileItemWriter<InventoryFileItem> dupItemWriter(){

        return new FlatFileItemWriterBuilder<InventoryFileItem>()
                .name("duplicateItemWriter")
                .resource(new FileSystemResource("duplicateItem.txt"))
                .lineAggregator(new PassThroughLineAggregator<>())
                .append(true)
                .shouldDeleteIfExists(true)
                .build();
    }


public class StepSkipListener implements SkipListener<InventoryFileItem, InventoryItem> {

    private FlatFileItemWriter<InventoryFileItem> skippedItemsWriter;
    
    public StepSkipListener(FlatFileItemWriter<InventoryFileItem> skippedItemsWriter) {
        this.skippedItemsWriter = skippedItemsWriter;
    }
    @Override
    public void onSkipInProcess(InventoryFileItem item, Throwable t) {
        System.out.println(item.getBibNum() + " Process - " + t.getMessage());
        
        try {
            skippedItemsWriter.write(Collections.singletonList(item));
        } catch (Exception e) {
            System.out.println(e.getMessage());
        }
    }

The overall Job is defined as below and I'm using the duplicateItemWriter from the SkipListener.

@Bean(name = "fileLoadJob")
    @Autowired
    public Job fileLoadJob(JobBuilderFactory jobs, StepBuilderFactory steps,
            FlatFileItemReader<inventoryFileItem> fileItemReader,
            CompositeItemProcessor compositeItemProcessor,
            @Qualifier(value = "itemWriter") ItemWriter<InventoryItem> itemWriter,
            StepSkipListener skipListener) {

        return jobs.get("libraryFileLoadJob")
                .start(steps.get("step").<InventoryFileItem, InventoryItem>chunk(chunkSize)
                        .reader(FileItemReader)
                        .processor(compositeItemProcessor)
                        .writer(itemWriter)
                        .faultTolerant()
                        .skip(Exception.class)
                        .skipLimit(Integer.parseInt(skipLimit))
                        .listener(skipListener)
                        .build())
                .build();
    }

I've also tried to write all data to FlatFileItemWriter - that doesn't work as well. However if write to a DB, then there's no issue with it.

The Spring-Batch version I'm using is - 4.3.3 I've referred to the below threads as well:

• unit testing a FlatFileItemWriter outside of Spring - "Writer must be open before it can be written to" exception
• Spring Batch WriterNotOpenException
• FlatfileItemWriter with Compositewriter example

This was just gross oversight, I missed that the FlatFileItemWriter needs a stream. I'm somewhat disappointed to put up this question, but I'm posting the answer just in case it helps someone.

The solution was as simple as adding a stream(dupItemWriter) to the Job Definition.

FlatfileItemWriter with Compositewriter example

@Bean(name = "fileLoadJob")
    @Autowired
    public Job fileLoadJob(JobBuilderFactory jobs, StepBuilderFactory steps,
            FlatFileItemReader<inventoryFileItem> fileItemReader,
            CompositeItemProcessor compositeItemProcessor,
            @Qualifier(value = "itemWriter") ItemWriter<InventoryItem> itemWriter,
@Qualifier(value = "duplicateItemWriter")FlatFileItemWriter<InventoryFileItem> dupItemWriter,
            StepSkipListener skipListener) {

        return jobs.get("libraryFileLoadJob")
                .start(steps.get("step").<InventoryFileItem, InventoryItem>chunk(chunkSize)
                        .reader(FileItemReader)
                        .processor(compositeItemProcessor)
                        .writer(itemWriter)
                        .faultTolerant()
                        .skip(Exception.class)
                        .skipLimit(Integer.parseInt(skipLimit))
                        .listener(skipListener)
                        .stream(dupItemWriter)
                        .build())
                .build();
    }