code: public JobStatus readJobStatus(JobID jobId) {
      JobStatus jobStatus = null;
      
      if (null == jobId) {
        LOG.warn("Could not read job status for null jobId");
        return null;
      }
      
      if (active) {
        try {
          FSDataInputStream dataIn = getJobInfoFile(jobId);
          if (dataIn != null) {
            jobStatus = readJobStatus(dataIn);
            dataIn.close();
          }
        } catch (IOException ex) {
          LOG.warn("Could not read [" + jobId + "] job status : " + ex, ex);
        }
      }
      return jobStatus;
    }
docs: This method retrieves JobStatus information from DFS stored using
  store method.
  
  @param jobId the jobId for which jobStatus is queried
  @return JobStatus object, null if not able to retrieve