title: cron expression with spring quartz
body: <p>How to write cron expressions for below?</p>
  
  <ol>
  <li>first working day  of each month at 00:00:00</li>
  <li>4th working day of each month at 06:00:00</li>
  <li>00:00:00 on saturday</li>
  </ol>
  
  <p>Based on above cron expression, how to get start date and end date?</p>
  
  <ol>
  <li>first day of prior month and first day of present month</li>
  <li>1st of previous month and 3 rd working day of present month</li>
  <li>Date of monday on present week and date of staturday of present week.</li>
  </ol>