Since in log4j javadoc is
WARNING: This version of JDBCAppender is very likely to be completely replaced in the future. Moreoever, it does not log exceptions.
What should I do to log to a database?
If you are looking for a database appender which not only works, but also supports connection pooling, is maintained and properly documented, than consider logback's DBAppender.
Ironically enough, the warning in the javadocs about removing JDBCAppender in future versions of log4j was written by me.