How to get starttime and endtime from Gatling resource code

Hi all,
I want to get the starttime and endtime, and I want try
DataReader dataReader = DataReader.newInstance(SystemConf.gatlingResultsFilePath) ;

but it goes wrong
Exception in thread “pool-1-thread-1” java.lang.NullPointerException
at io.gatling.core.result.reader.DataReader$.newInstance(DataReader.scala:25)
at io.gatling.core.result.reader.DataReader.newInstance(DataReader.scala)

How can I get them

Could you explain what you’re trying to do, please?