What does rootCategory in log4j.properties mean?

Question

log4j.rootCategory field in log4j.properties can have 4 different values, namely: DEBUG, WARN, INFO and ERROR.

Can you tell me which is most suitable for which cases?

Answer 1

From the least severe to the most one:

ALL < DEBUG < INFO < WARN < ERROR < FATAL < OFF

If you choose one of them log4j will generate all messages of that type and of more severe type.

Purposes:

• ALL: generates all messages*
• DEBUG: debug messages
• INFO: information that aren't problems
• WARN: not error but something that could cause a future error
• ERROR: something went wrong, a problem that the application manages, the application could be stopped or not, usually must be reported
• FATAL: an error that crashes the application
• OFF: generates no messages*

(*) these are only keywords; for these categories there are no methods all(msg) and off(msg), like we have error(msg) or debug(msg).

Usually

• during development I set
  • logging on file to ALL or DEBUG
• when deployed I set
  • logging on file to INFO or WARN
  • logging via email to ERROR