Spring Batch step not executing

Question

I am working on a spring batch project in which I am reading a list of students, processing it and writing it.

For now I have kept it simple and processing just returns the student and write just prints it.

I was expecting every-time the step runs I will see the output but I see it only once when the step runs for the first time. Below is the output

2020-04-03 01:33:16.153  INFO 14710 --- [           main] o.s.batch.core.job.SimpleStepHandler     : Executing step: [xxxx]
[Student{id=1, name='ABC'}]
as
[Student{id=2, name='DEF'}]
as
[Student{id=3, name='GHI'}]
as
2020-04-03 01:33:16.187  INFO 14710 --- [           main] o.s.batch.core.step.AbstractStep         : Step: [xxxx] executed in 33ms
2020-04-03 01:33:16.190  INFO 14710 --- [           main] o.s.b.c.l.support.SimpleJobLauncher      : Job: [SimpleJob: [name=readStudents]] completed with the following parameters: [{}] and the following status: [COMPLETED] in 52ms
job triggered
2020-04-03 01:33:17.011  INFO 14710 --- [   scheduling-1] o.s.b.c.l.support.SimpleJobLauncher      : Job: [SimpleJob: [name=readStudents]] launched with the following parameters: [{time=1585857797003}]
2020-04-03 01:33:17.017  INFO 14710 --- [   scheduling-1] o.s.batch.core.job.SimpleStepHandler     : Executing step: [xxxx]
2020-04-03 01:33:17.022  INFO 14710 --- [   scheduling-1] o.s.batch.core.step.AbstractStep         : Step: [xxxx] executed in 4ms
2020-04-03 01:33:17.024  INFO 14710 --- [   scheduling-1] o.s.b.c.l.support.SimpleJobLauncher      : Job: [SimpleJob: [name=readStudents]] completed with the following parameters: [{time=1585857797003}] and the following status: [COMPLETED] in 11ms

Also I notice that first time there are no parameters in job and after that there are parameters. Whereas I am supplying job parameters whenever I run job.

Config file

@EnableBatchProcessing
public class Config {

  private JobRunner jobRunner;

  public Config(JobRunner jobRunner){
    this.jobRunner = jobRunner;
  }

  @Scheduled(cron = "* * * * * *")
  public void scheduleJob() throws JobParametersInvalidException, JobExecutionAlreadyRunningException, JobRestartException, JobInstanceAlreadyCompleteException {
    System.out.println("job triggered");
    jobRunner.runJob();
  }
}

@Configuration
public class JobConfig {
  @Bean
  public Job job(JobBuilderFactory jobBuilderFactory,
                 StepBuilderFactory stepBuilderFactory,
                 ItemReader<Student> reader,
                 ItemProcessor<Student, Student> processor,
                 ItemWriter<Student> writer) {

    Step step = stepBuilderFactory.get("xxxx")
        .<Student, Student>chunk(1)
        .reader(reader)
        .processor(processor)
        .writer(writer)
        .build();

    return jobBuilderFactory
        .get("readStudents")
        .start(step)
        .build();
  }

  @Bean
  public ItemReader<Student> reader() {
    return new InMemoryStudentReader();
  }
}

Job runner file

public class JobRunner {

  private Job job;
  private JobLauncher simpleJobLauncher;

  @Autowired
  public JobRunner(Job job, JobLauncher jobLauncher) {
    this.simpleJobLauncher = jobLauncher;
    this.job = job;
  }


  public void runJob() throws JobParametersInvalidException, JobExecutionAlreadyRunningException, JobRestartException, JobInstanceAlreadyCompleteException {
    JobParameters jobParameters =
        new JobParametersBuilder()
            .addLong("time",System.currentTimeMillis()).toJobParameters();
    simpleJobLauncher.run(job, jobParameters);

  }
}

In memory student reader

public class InMemoryStudentReader implements ItemReader<Student> {

  private int nextStudentIndex;
  private List<Student> studentData;

  public InMemoryStudentReader() {
    initialize();
  }

  private void initialize() {
    Student s1 = new Student(1, "ABC");
    Student s2 = new Student(2, "DEF");
    Student s3 = new Student(3, "GHI");

    studentData = Collections.unmodifiableList(Arrays.asList(s1, s2,s3));
    nextStudentIndex = 0;
  }

  @Override
  public Student read() throws Exception {
    Student nextStudent = null;

    if (nextStudentIndex < studentData.size()) {
      nextStudent = studentData.get(nextStudentIndex);
      nextStudentIndex++;
    }

    return nextStudent;
  }
}

Answer 1

Because you are calling initialize() in InMemoryStudentReader constructor. Spring only initialize InMemoryStudentReader once and wire it to your job. After the first run, nextStudentIndex is not reset to 0. So the next time your job runs, your reader cannot read anymore.

If you want it to work, you should reset the nextStudentIndex to 0 whenever you start your job.