public void setDatePattern(String pattern) {
        datePattern = pattern;
    }
The <b>DatePattern</b> takes a string in the same format as expected by
{@link SimpleDateFormat}. This options determines the rollover schedule.
metamorphosis-client-extension/src/main/java/com/taobao/metamorphosis/client/extension/log4j/DailyRollingFileStreamAppender.java