For this example to work you'll need a JDBC driver compatible to the system the database is running on. An opensource one that allows you to connect to DB2 databases on an IBM System i can be found here: JT400
Even though this example is DB2 specific, it works for almost every other system if you exchange the driver and adapt the JDBC URL.
# Root logger option
log4j.rootLogger= ERROR, DB
# Redirect log messages to a DB2
# Define the DB appender
log4j.appender.DB=org.apache.log4j.jdbc.JDBCAppender
# Set JDBC URL (!!! adapt to your target system !!!)
log4j.appender.DB.URL=jdbc:as400://10.10.10.1:446/DATABASENAME;naming=system;errors=full;
# Set Database Driver (!!! adapt to your target system !!!)
log4j.appender.DB.driver=com.ibm.as400.access.AS400JDBCDriver
# Set database user name and password
log4j.appender.DB.user=USER
log4j.appender.DB.password=PASSWORD
# Set the SQL statement to be executed.
log4j.appender.DB.sql=INSERT INTO DB.TABLENAME VALUES('%d{yyyy-MM-dd}','%d{HH:mm:ss}','%C','%p','%m')
# Define the layout for file appender
log4j.appender.DB.layout=org.apache.log4j.PatternLayout