improve JobParameters to Non ThreadLocal

JobParameters are managed by org.springframework.batch.core.scope.context.SynchronizationManagerSupport#executionHolder using ThreadLocal, which prevents SpEL bindings (@Value("#{jobParameters['param']}")) from working correctly in other threads.

However, JobParameters are typically read-only and do not change during batch execution. In a multi-threaded step (TaskExecutor), this ThreadLocal management causes access to JobParameters within JobScope or StepScope beans to fail.

I’m not sure why JobParameters need to be managed within a ThreadLocal JobContext. Could JobParameters be modified to be non-ThreadLocal instead?

I’m using a class that encapsulates JobParameters. However, access to this class's fields fails when accessed within a JobScope (or StepScope) bean in a multi-threaded step.

encapsulates JobParameters

@JobScope
@Component
public class MyJobParameters {

    @Value("#{jobParameters['firstParam']}")
    private String firstParam;

    @Value("#{jobParameters['secondParam']}")
    private String secondParam;

    public String getFirstParam() {
        return firstParam;
    }

    public String getSecondParam() {
        return secondParam;
    }
}

failed (multi thread step)

    public Step myMultiThreadStep() {
        return new StepBuilder("chunkWorkingStep", jobRepository)
                .<Sample, Sample>chunk(500, new ResourcelessTransactionManager())
                .reader(myReader())
                .processor(myProcessor())
                .writer(myWriter())
                .taskExecutor(taskExecutor())
                .build();
    }
    
    public ItemProcessor<Sample, Sample> myProcessor() {
        String firstParam = myJobParameters.getFirstParam(); // failed
        return item -> {
                   String secondParam = myJobParameters.getSecondParam(); // failed
            return item;
        };
    }

ok (non multi thread step)

    public Step myStep() {
        return new StepBuilder("chunkWorkingStep", jobRepository)
                .<Sample, Sample>chunk(500, new ResourcelessTransactionManager())
                .reader(myReader())
                .processor(myProcessor())
                .writer(myWriter())
                .build();
    }
    
    public ItemProcessor<Sample, Sample> myProcessor() {
        String firstParam = myJobParameters.getFirstParam(); // ok
        return item -> {
                   String secondParam = myJobParameters.getSecondParam(); // ok
            return item;
        };
    }

If there’s anything I might be missing or not understanding, please let me know.

Start with org.springframework.batch.core.scope.context.SynchronizationManagerSupport#executionHolder and trace how JobParameters are resolved for JobScope and StepScope beans. Reproduce the supplied multi-threaded-step example, then define tests showing that SpEL JobParameters bindings remain available across worker threads without breaking existing scope behavior.