code: public static void processButtons(HttpServletRequest request,
        HttpServletResponse response, JobTracker tracker) throws IOException {
  
      if (conf.getBoolean(PRIVATE_ACTIONS_KEY, false)
          && request.getParameter("killJobs") != null) {
        String[] jobs = request.getParameterValues("jobCheckBox");
        if (jobs != null) {
          for (String job : jobs) {
            tracker.killJob(JobID.forName(job));
          }
        }
      }
  
      if (conf.getBoolean(PRIVATE_ACTIONS_KEY, false) &&
            request.getParameter("changeJobPriority") != null) {
        String[] jobs = request.getParameterValues("jobCheckBox");
  
        if (jobs != null) {
          JobPriority jobPri = JobPriority.valueOf(request
              .getParameter("setJobPriority"));
  
          for (String job : jobs) {
            tracker.setJobPriority(JobID.forName(job), jobPri);
          }
        }
      }
    }
docs: Method used to process the request from the job page based on the
  request which it has received. For example like changing priority.
  
  @param request HTTP request Object.
  @param response HTTP response object.
  @param tracker {@link JobTracker} instance
  @throws IOException