How can I configure Log4j to send different logging levels to separate appenders and log files?

Logging Different Levels and Content with Log4j

Question:

Can log4j be configured to direct different logging levels to separate appenders? The goal is to create multiple log files with specific content, such as a main log catching all INFO and above messages, while another log captures DEBUG messages for only a selected group of classes.

Answer:

Configuring Log4j for Multiple Log Files

Log4j allows customization of logging to multiple destinations through appenders. To achieve the desired configuration:

1. Define Multiple Appenders: Start by creating separate appenders for each type of log. Assign them appropriate File attributes to specify their log file destination. Set the Threshold to control the logging level for each appender (e.g., INFO for main log and DEBUG for specific classes).
2. Configure Root Logger: The rootLogger option determines where all logging is initially sent. Configure it to send logs to the appenders you created earlier.
3. Set Logger Levels: Use the log4j.logger property to set specific logging levels for different classes or packages. This allows you to selectively control the level of detail logged for each class.

Example Configuration:

log4j.rootLogger=QuietAppender, LoudAppender, TRACE
# setup main log
log4j.appender.QuietAppender=org.apache.log4j.RollingFileAppender
log4j.appender.QuietAppender.Threshold=INFO
log4j.appender.QuietAppender.File=quiet.log

# setup specific log
log4j.appender.LoudAppender=org.apache.log4j.RollingFileAppender
log4j.appender.LoudAppender.Threshold=DEBUG
log4j.appender.LoudAppender.File=loud.log

# set logging level for specific classes
log4j.logger.com.yourpackage.yourclazz=TRACE

With this configuration, the 'quiet.log' will contain all INFO and above messages for all classes, while 'loud.log' will only contain DEBUG messages for the specified class 'yourclazz'.

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