I am looking for some kind of analyzer tool for log files generated by log4j files. I am looking something more advanced than grep? What are you using for log file analysis?

I am looking for following kinds of features:

• The tool should tell me how many time a given log statement or a stack trace has occurred, preferably with support for some kinds of patterns (eg. number of log statements matching 'User [a-z]* logged in').
• Breakdowns by log level (how many INFO, DEBUG lines) and by class that initiated the log message would be nice.
• Breakdown by date (how many log statements in given time period)
• What log lines occur commonly together?
• Support for several files since I am using log rolling
• Hot spot analysis: find if there is a some time period when there is unusually high number of log statements
• Either command-line or GUI are fine
• Open Source is preferred but I am also interested in commercial offerings

My log4j configuration uses org.apache.log4j.PatternLayout with pattern %d %p %c - %m%n but that could be adapted for analyzer tool.