ItemWriter not producing output when having a StepScope annotation to access parameter in ItemReader in Spring Batch

I'm using a spring boot with spring batch application to test passing a parameter to the ItemReader by using below code, but the content of contact-out.dat file (which is the output file) is empty when I use StepScope annotation. There's no error, it just doesn't produce any result:

@Bean
@StepScope
public ItemReader<Contact> reader(@Value("#{jobParameters['fileName']}") String fileName) {    	    	
BeanIOFlatFileItemReader<Contact> reader = new BeanIOFlatFileItemReader<>();
try {    		
reader.setUseSpringExceptions(true);
reader.setResource(new FileSystemResource(fileName));
reader.setStreamName(inputContactStreamName);
reader.setStreamMapping(new ClassPathResource(beanIoConfigurationXmlPath));
reader.setStreamFactory(StreamFactory.newInstance());
reader.getLineNumber();
reader.afterPropertiesSet();
} catch (Exception e) {
log.error("ERROR: An issue occurred in the BeanIO Item Reader:: {} {}", e.getMessage(), e.getStackTrace());
}
return reader;    	
}    
@Bean
public FlatFileItemWriter<Contact> writer() {
FlatFileItemWriter<Contact> writer = new FlatFileItemWriter<>();
writer.setResource(new FileSystemResource(fileOutputContact));
writer.setLineAggregator(new DelimitedLineAggregator<Contact>() {
{
setDelimiter(",");
setFieldExtractor(new BeanWrapperFieldExtractor<Contact>() {
{
setNames(new String[] { "firstName", "lastName", "street", "city", "state", "zip" });
}    				
});
}
});
return writer;
}
@Bean("InputJob")
@Scope(value = ConfigurableBeanFactory.SCOPE_PROTOTYPE)
public Job importUserJob(Step step) {
return jobBuilderFactory.get("importUserJob")
.incrementer(new RunIdIncrementer())          
.flow(step)
.end()
.build();
}
@Bean
public Step step(ItemReader<Contact> reader) {    	
return stepBuilderFactory.get("step")
.<Contact, Contact> chunk(10)
.reader(reader(null))          
.processor(contactItemProcessor)
.writer(writer())          
.build();
}

Now, if I remove the StepScope annotation and make below changes then contact-out.dat file has the expected content:

@Bean
//@StepScope
public ItemReader<Contact> reader(/*@Value("#{jobParameters['fileName']}") String fileName*/) {...}
@Bean
public Step step(ItemReader<Contact> reader) {    	
return stepBuilderFactory.get("step")
.<Contact, Contact> chunk(10)
.reader(reader(/*null*/))          
.processor(contactItemProcessor)
.writer(writer())          
.build();
}

What I'm doing wrong here when using StepScope annotation that ouput file is always empty?

When using @Configuration classes the best thing to do for @Bean methods is to be as specific as possible about the type. As this type information is used at load time to determine what callbacks to do or what proxy to create.

When you are adding an @StepScope what happens is that a lazy proxy is created for the argument type of the method. In your case that is an ItemReader<Contact>. If you check the javadoc of the FlatFileItemReader you see that it implements more interfaces. Those interfaces are needed by Spring Batch to do the appropriate callbacks to initialize the reader. However if it is an ItemReader those callbacks aren't there.

@Bean
@StepScope
public BeanIOFlatFileItemReader<Contact> reader(@Value("#{jobParameters['fileName']}") String fileName) {             
    BeanIOFlatFileItemReader<Contact> reader = new BeanIOFlatFileItemReader<>();
    reader.setUseSpringExceptions(true);
    reader.setResource(new FileSystemResource(fileName));
    reader.setStreamName(inputContactStreamName);
    reader.setStreamMapping(new ClassPathResource(beanIoConfigurationXmlPath));
    reader.setStreamFactory(StreamFactory.newInstance());
    reader.getLineNumber();
    return reader;          
}

With this the proper proxy will be created and all the callbacks will be effective.

In your configuration you are already injecting the ItemReader as an argument use that instead of calling reader(null).

@Bean
public Step step(BeanIOFlatFileItemReader<Contact> reader) {      
    return stepBuilderFactory.get("step")
      .<Contact, Contact> chunk(10)
      .reader(reader)          
      .processor(contactItemProcessor)
      .writer(writer())          
      .build();
}