DailyRollingFileAppender may be the option that you are looking for.
You can specify your appender in the appender option of your log4j.properties file like this
log4j.rootCategory=ALL, STDOUT, ROLLFILE
log4j.appender.ROLLFILE=org.apache.log4j.DailyRollingFileAppender
from javadoc of log4j api.
The rolling schedule is specified by the DatePattern option. This pattern should follow the SimpleDateFormat conventions. In particular, you must escape literal text within a pair of single quotes. A formatted version of the date pattern is used as the suffix for the rolled file name.
For example, if the File option is set to /foo/bar.log and the DatePattern set to '.'yyyy-MM-dd, on 2001-02-16 at midnight, the logging file /foo/bar.log will be copied to /foo/bar.log.2001-02-16 and logging for 2001-02-17 will continue in /foo/bar.log until it rolls over the next day.
Hope this helps,
Regards,