How to log FATAL (or any custom log level) with SLF4J and Log4j2

Question

I have those specific requirements :

• Need to be able to log in FATAL level
• Need to use SLF4J
• Need to use Log4j2

Right now, here's my implementation:

final Logger logger = LoggerFactory.getLogger(HelloWorld.class);
final Marker marker = MarkerFactory.getMarker("FATAL");
logger.error(marker, "!!! Fatal World !!!");

Here's my PatternLayout (in yaml):

PatternLayout:
  Pattern: "%d{ISO8601_BASIC} %-5level %marker [%t] %logger{3.} - %msg%n"

Here's my log output :

20150506T155705,158 ERROR FATAL [main] - !!! Fatal World !!!

Do you have any idea about how to efficiently to remove the "ERROR" from the log output?

Thank you very much

Answer 1

Marker is not really what you want here. Marker is for "enriching" log messages, making them more easily searchable. You are trying to change the log level/priority, which is a little different.

You're using logger.error() which will log the message as an ERROR level.

If there is no FATAL level pre-defined (usually there is, such as logger.fatal()), then use the generic logger.log() which allows you to specify the log level.

logger.fatal(yourMessage);

OR

logger.log(priorityLevel, yourMessage);

UPDATE:

From the SLF4J website:

The Marker interface, part of the org.slf4j package, renders the FATAL level largely redundant. If a given error requires attention beyond that allocated for ordinary errors, simply mark the logging statement with a specially designated marker which can be named "FATAL" or any other name to your liking.

http://www.slf4j.org/faq.html#fatal

So, with SLF4J, it is not possible to have a FATAL log level. I strongly disagree with the rationale behind this decision, but it is what it is.

Answer 2

Here's the closest working solution I came with some colleagues :

1. Create a Fatal Marker class using SLF4J Markers.
2. Using a RoutingAppender, use the Marker as the routing pattern: "$${marker:}"
3. Configure a Fatal-specific appender that has its own PatternLayout that doesn't include the LogLevel but a hardcoded FATAL level.

Here's the Java sample :

Marker fatal = MarkerFactory.getMarker("FATAL");
// Usage example
final Logger logger = LoggerFactory.getLogger(FatalLogger.class);
logger.log(fatal, "this is a fatal message");

// Log sample : 
20150514T115144,279  FATAL [main] FatalLogger - this is a fatal message

Here's the YAML sample :

Configuration:
  status: debug

  Appenders:
    RandomAccessFile:
      - name: APPLICATION_APPENDER
        fileName: logs/application.log
        PatternLayout:
          Pattern: "%d{ISO8601_BASIC} %-5level %msg%n"
      - name: FATAL_APPENDER
        fileName: logs/application.log
        PatternLayout:
          Pattern: "%d{ISO8601_BASIC} FATAL %msg%n"

    Routing:
      name: ROUTING_APPENDER
      Routes:
        pattern: "$${marker:}"
        Route:
        - key: FATAL
          ref: FATAL_APPENDER
        - ref: APPLICATION_APPENDER #DefaultRoute

  Loggers:
    Root:
      level: trace
      AppenderRef:
        - ref: ROUTING_APPENDER

Answer 3

I know the question is for log4j. I found this page when looking in relation to logback. Here's what sl4j recommends: https://www.slf4j.org/faq.html#fatal.