In some cases we have to write logs to different outputs
according to log level. It can be easily configured by specifying the filter of
certain appenders. The most easiest way of specifying appenders is having a properties
configuration file, but properties configuration files doesn’t support log
level filters. Therefore it is necessary to stick with XML to specify
appenders.
Log4J supports different log levels. These log levels can be
used in different events as mentioned in table 1.
#
|
Level
|
Summary
|
1
|
ALL
|
ALL has the lowest rank and it is intended to turn on all logging.
|
2
|
DEBUG
|
DEBUG level is useful to developers to indentify events in an
informational manner and allows to debug the application.
|
3
|
ERROR
|
ERROR level specifies events that must immediately investigated but
which allows the application to continue its functionality.
|
4
|
FATAL
|
FATAL level can be used to log terrible errors that can cause
application to abort its operations.
|
5
|
INFO
|
INFO level is useful to mention informative messages after important process
has finished.
|
6
|
OFF
|
OFF has the highest rand and it is intended to turn off all logging.
|
7
|
TRACE
|
TRACE level is used to log events in a very informative manner.
Basically TRACE logs are used in development and eventually remove from
production deployments.
|
8
|
WARN
|
WARN level can be used to log potentially harmful situations.
|
Basically when a low priority log level is given, messages
with higher priority for the given log level are also logged. In that case log
level range filter (LevelRangeFilter) can be used to reject messages with
priorities outside a certain range. The range can be configured by specifying
the values for LevelMin, LevelMax, and AcceptOnMatch properties.
A sample of log4j XML file with log level filters created by
a colleague is added below.
References:
References:
- "Logging Services." Log4J. Apache Software Foundation, n.d. Web.
- "Log4j Architecture." Log4J. Apache Software Foundation, n.d. Web.
