What does these properties in log4j.properties mean?

问题

log4j.rootCategory feild in log4j.properties can have 4 different values namely:

DEBUG,WARN,INFO and ERROR. Can you tell me which is most suitable for what cases?

回答1:

From the least severe to the most one:

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

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

Purposes:

• ALL: prints 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: prints 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 to ALL or DEBUG, while when deployed I set to INFO or WARN.

来源：https://stackoverflow.com/questions/4933707/what-does-these-properties-in-log4j-properties-mean