ItemWriter not outputting rows how I would like - spring

Question

I've written a spring batch job to read from a database and then write to a csv.
The job works but unfortunately in my output CSV file it just puts whatever is in the toString method of my Domain Object.
What I am really after is all the values in the bean separated by a comma. Which is why in my ItemWriter below I put in a DelimitedLineAggregator.
But I think my understanding of that DelimitedLineAggregator is wrong. I thought that the LineAggregator was used for the output but now I think it's used for the input data.
#Bean
#StepScope
public ItemWriter<MasterList> masterListFileWriter(
FileSystemResource masterListFile,
#Value("#{stepExecutionContext}")Map<String, Object> executionContext) {
FlatFileItemWriter<MasterList> writer = new FlatFileItemWriter<>();
writer.setResource(masterListFile);
DelimitedLineAggregator<MasterList> lineAggregator = new DelimitedLineAggregator<>();
lineAggregator.setDelimiter(";");
writer.setLineAggregator(lineAggregator);
writer.setForceSync(true);
writer.open(new ExecutionContext(executionContext));
return writer;
}
Two things.
What can I change to output all the values of my MasterList domain object separated by a comma? Is changing the toString method the only way?
Also can someone clarify the use of the LineAggregator in the writer. I'm now thinking it's used to specify how you want to aggregate lines coming from your Reader. Is that right?
Thanks in advance

Answer 1

I worked this out by adding a BeanWrapperFieldExtractor to the writer.
#Bean
#StepScope
public ItemWriter<MasterList> masterListFileWriter(
FileSystemResource masterListFile,
#Value("#{stepExecutionContext}")Map<String, Object> executionContext) {
FlatFileItemWriter<MasterList> writer = new FlatFileItemWriter<>();
writer.setResource(masterListFile);
DelimitedLineAggregator<MasterList> lineAggregator = new DelimitedLineAggregator<>();
lineAggregator.setDelimiter(",");
BeanWrapperFieldExtractor<MasterList> extractor = new BeanWrapperFieldExtractor<MasterList>();
extractor.setNames(new String[] { "l2", "l2Name"});
lineAggregator.setFieldExtractor(extractor);
writer.setLineAggregator(lineAggregator);
writer.setForceSync(true);
writer.open(new ExecutionContext(executionContext));
return writer;
}