title: how to append date to log file name using RollingFileAppender
body: <p>i'm using log4j RollingFileAppender , i'm trying to append date to file name </p>
  
  <p>so i append "-%d{yyyy-MM-dd_HH-mm}." to active file name property in log4j.properties like below , however file is generated  with name mylog-%d{yyyy-MM-dd_HH-mm}.log without setting the date </p>
  
  <p>log4j.appender.mylog.rollingPolicy.ActiveFileName=mylog-%d{yyyy-MM-dd_HH-mm}.log</p>
  
  <p>any helping ideas ??</p>