use DailyRollingFileAppender , propertys set as underside :
log4j.appender.R=org.apache.log4j.RollingFileAppender
log4j.appender.dailyFile.bufferSize=2048
log4j.appender.dailyFile.immediateFlush=false
log4j.appender.dailyFile.bufferedIO=true

when JVM Process finish, there is some data in io buffer not flush to disk.
FileAppender RollingFileAppender maybe have same problem.

public DailyRollingFileAppender()

{ // set when JVM Process finish , flush buffer to disk // in my project to extend DailyRollingFileAppender,use this method. maybe your can reference Runtime.getRuntime().addShutdownHook( ...... ); }