春季批处理：执行异步作业时，CustomItemWriter中出现NullPointerException

Question

我正在使用带有4.2.1.RELEASE版本的spring batch。我有一份工作，我使用不同的工作参数多次运行。同步执行作业时，一切正常。当我尝试异步运行作业时，在尝试从CustomItemWriter的执行上下文中获取某些值时，我得到了NullPointerException。作业由作业调度程序调度。

CustomItemWriter

public class CustomWriter ItemWriter<T>, StepExecutionListener {
    private CustomObject customObject;

    @Override
    public void beforeStep(StepExecution stepExecution) {
        ExecutionContext executionContext = stepExecution.getJobExecution().getExecutionContext();
        customObject = (CustomObject) Objects.requireNonNull(executionContext.get("custom_object")); -> Exception when running asynchronous
    }

    @Override
    public void write(List<? extends CustomWriter> list) {
        // do something
    }

    @Override
    public ExitStatus afterStep(StepExecution stepExecution) {
        return ExitStatus.COMPLETED;
    }
}

BatchConfig

public class BatchConfig extends DefaultBatchConfigurer {
    @Autowired
    @Qualifier("batchDataSource")
    private DataSource batchDataSource;

    @Autowired
    private PlatformTransactionManager platformTransactionManager;

    @Autowired
    private JobRepository jobRepository;

    @Override
    @Autowired
    public void setDataSource(@Qualifier("batchDataSource") final DataSource batchDataSource) {
        super.setDataSource(batchDataSource);
    }

    @Bean
    public BatchDataSourceInitializer batchDataSourceInitializer(
            @Qualifier("batchDataSource") final DataSource batchDataSource, final ResourceLoader resourceLoader) {
        return new BatchDataSourceInitializer(batchDataSource, resourceLoader, new BatchProperties());
    }

    @Override
    public JobRepository createJobRepository() throws Exception {
        Jackson2ExecutionContextStringSerializer defaultSerializer = new Jackson2ExecutionContextStringSerializer();
        defaultSerializer.setObjectMapper(JsonUtils.getObjectMapper());

        JobRepositoryFactoryBean factory = new JobRepositoryFactoryBean();
        factory.setDataSource(batchDataSource);
        factory.setTransactionManager(platformTransactionManager);
        factory.setSerializer(defaultSerializer);
        factory.afterPropertiesSet();

        return factory.getObject();
    }

    @Bean
    public JobLauncher asyncJobLauncher() throws Exception {
        SimpleJobLauncher jobLauncher = new SimpleJobLauncher();
        jobLauncher.setJobRepository(jobRepository);
        jobLauncher.setTaskExecutor(new SimpleAsyncTaskExecutor());
        jobLauncher.afterPropertiesSet();
        return jobLauncher;
    }
}

MainClass

@EnableScheduling
@EnableAsync
@SpringBootApplication
@Import({BatchConfig.class, DataSourceConfig.class, MainJobConfig.class})
public class App {
    public static void main(String[] args) {
        SpringApplication.run(App.class, args);
    }
}

异常（仅在异步执行作业时发生）

java.lang.NullPointerException: null
    at java.util.Objects.requireNonNull(Objects.java:203)
    at com.aldisued.tcmapp.chunks.writer.CustomItemWriter.beforeStep(CustomItemWriter.java:22)
    at org.springframework.batch.core.listener.CompositeStepExecutionListener.beforeStep(CompositeStepExecutionListener.java:79)
    at org.springframework.batch.core.step.AbstractStep.execute(AbstractStep.java:204)
    at org.springframework.batch.core.job.SimpleStepHandler.handleStep(SimpleStepHandler.java:148)
    at org.springframework.batch.core.job.flow.JobFlowExecutor.executeStep(JobFlowExecutor.java:68)
    at org.springframework.batch.core.job.flow.support.state.StepState.handle(StepState.java:68)
    at org.springframework.batch.core.job.flow.support.SimpleFlow.resume(SimpleFlow.java:169)
    at org.springframework.batch.core.job.flow.support.SimpleFlow.start(SimpleFlow.java:144)
    at org.springframework.batch.core.job.flow.FlowJob.doExecute(FlowJob.java:137)
    at org.springframework.batch.core.job.AbstractJob.execute(AbstractJob.java:319)
    at org.springframework.batch.core.launch.support.SimpleJobLauncher$1.run(SimpleJobLauncher.java:147)
    at java.lang.Thread.run(Thread.java:748)

JobScheduler

@Component
public class JobScheduler {
    @Autowired
    private Environment environment;

    @Autowired
    @Qualifier("asyncJobLauncher")
    private JobLauncher jobLauncher;

    @Autowired
    private Job job;

    @Scheduled(cron = "${job.cron.expr}")
    public void runJob() throws JobParametersInvalidException, JobExecutionAlreadyRunningException,
            JobRestartException, JobInstanceAlreadyCompleteException, InterruptedException {
        runJobs(getStringList();
    }

    private void runJobs(List<String> stringList) throws JobParametersInvalidException,
            JobExecutionAlreadyRunningException, JobRestartException, JobInstanceAlreadyCompleteException {
        for (String string : stringList) {
            JobParameters params = new JobParametersBuilder()
                    .addDate("exec_time", new Date())
                    .addString("exec_time", string)
                    .toJobParameters();

            jobLauncher.run(job, params);
        }
    }

    private List<Strings> getStringList() {
        // get some strings
    }
}

我如何使执行线程安全或我做错了什么？