How to run a SQL only once which is required for processing the read data in spring batch

I am new to Spring Batch, I have a spring boot app inn which i run a Spring batch job which executes a series of step, on one of the steps, I read thousands of record from a DB and process them and write it to a file. while processing I need a data from another table which i need to store in it a list, which i can use to process all the read data before writing them to a file again.

Is there a way where i can run that SQL only once common to all data?

`

@Configuration
public class JDBCStep {

  @Bean("JdbcStep")
  public Step  step() {
    
    return stepBuilderFactory.get("JdbcStep")
                .<ReadObject, WriteObject>chunk(10)
                .reader(reader)
                .processor(new processor())
                .writer(writer)
                .listener(new CustomStepListener())
                .build();
  }

  @Bean
  public ItemReader<StudentDTO> itemReader(DataSource dataSource,
                                             PagingQueryProvider queryProvider) {
        return new JdbcPagingItemReaderBuilder<StudentDTO>()
                .name("pagingItemReader")
                .dataSource(dataSource)
                .pageSize(1)
                .queryProvider(queryProvider)
                .rowMapper(new BeanPropertyRowMapper<>(SampleDTO.class))
                .build();
    } 

   public class Processor implements ItemProcessor<SampleDTO, OutputDTO>{
        @override
        public OutputDTO process(SampleDTO input){
           return ProcessService.processData(input)
        }
   }
}

public class CustomStepListener implements StepExecutionListener {

	@Override
	public void beforeStep(StepExecution stepExecution) {
		System.out.println("StepExecutionListener - beforeStep");
	}

	@Override
	public ExitStatus afterStep(StepExecution stepExecution) {
		System.out.println("StepExecutionListener - afterStep");
		return null;
	}

}


@Service
public class ProcessService{
    public OutputDTO processData(SampleDTO s){

        **Here For processing this data s, I need a List of ID from another table which is common for all the sampleDTO data to be processed. If i make a DB call in this method, It makes a DB call for all the record. Is there a way i can make a DB call only once to process all the data**
     
     Query q = entityManager.createQuery(query);
     List results = q.getResultList();

//I need the results for all the records to be processed.

}

You can implement StepExecutionListener to your processor class.

> StepExecutionListener represents the most generic listener for Step
> execution. It allows for notification before a Step is started and
> after it ends. https://docs.spring.io/spring-batch/docs/current/reference/html/step.html

Before the processor step, you can load ids once which will be used by all process data.

  public class Processor implements ItemProcessor<SampleDTO, OutputDTO>, StepExecutionListener {

    private static List<String> ids = new ArrayList<>();

    @Override
    public OutputDTO process(SampleDTO input) throws Exception {
        return new ProcessService().processData(input, ids);
    }

    @Override
    public void beforeStep(StepExecution stepExecution) {
        Query q = entityManager.createQuery(query);
        ids = q.getResultList();
    }

    @Override
    public ExitStatus afterStep (StepExecution stepExecution) {
        ids.clear();
        return stepExecution.getExitStatus();
    }
}

If you are using a custom StepExecutionListener you can also use the @BeforeStep annotation which will only be called once before the step is executed.

public class Processor implements ItemProcessor<SampleDTO, OutputDTO> {

    private final List<String> ids;

    public Processor(){
        ids = new ArrayList<>();
    }

    @BeforeStep
    public void beforeStepExecution() {
        Query q = entityManager.createQuery(query);
        ids = q.getResultList();
    }

    @Override
    public OutputDTO process(SampleDTO input) throws Exception {
        return new ProcessService().processData(input, ids);
    }

}