log4j: rotating log files based on time rather than size

Question

I use log4j with the "RollingFileAppender" to create a log rotation based on a certain size per file. How can I configure it to log to each file for a certain amount of time before rotating? For example, so that each log file contains one hour of logs, rotating at the top of each hour? BTW, I configure log4j programatically in Java using a Properties object (as opposed to a log4j.properties file)

Thanks for any help!

Answer 1

Use a DailyRollingFileAppender.

In particular, setting its 'datePattern' property to '.'yyyy-MM-dd-HH would cause file to rotate every hour.

Answer 2

You probably want to use a DailyRollingFileAppender. To roll them hourly, for example, you'd use a DatePattern of '.'yyyy-MM-dd-HH. For a log4j.properties file:

log4j.appender.myAppender=org.apache.log4j.DailyRollingFileAppender
log4j.appender.myAppender.DatePattern='.'yyyy-MM-dd-HH
...

Or for your programmatic configuration:

DailyRollingFileAppender appender = new DailyRollingFileAppender();
appender.setDatePattern("'.'yyyy-MM-dd-HH");

Logger root = Logger.getRootLogger();
root.addAppender(appender);

Unfortunately, using a DailyRollingFileAppender means that you can't limit the file size - this could be problematic if you have tons of logs in the given rolled period.

Answer 3

The other thing to be careful of with any rolling file appender is to make sure only one vm access a particular log file at a time. This is because log4j caches the log file size for performance reasons, and your 'rolling' will get wonky if multiple vm's access the sames files.

Answer 4

You need to use the DailyRollingFileAppender. Despite its misleading name it can be configured in a to run at configurable time periods up to minutes.