Log4j - Formatting Layouts

Log4j - File Appenders

log4j Resources

log4j - Logging Levels

Quiz

The org.apache.logging.log4j.Level levels. You can also define your custom levels by sub-classing the Level class.

Level	Description
ALL	All levels including custom levels.
DEBUG	Designates fine-grained informational events that are most useful to debug an application.
INFO	Designates informational messages that highlight the progress of the application at coarse-grained level.
WARN	Designates potentially harmful situations.
ERROR	Designates error events that might still allow the application to continue running.
FATAL	Designates very severe error events that will presumably lead the application to abort.
OFF	The highest possible rank and is intended to turn off logging.
TRACE	Designates finer-grained informational events than the DEBUG.

How do Levels Works?

A log request of level p in a logger with level q is enabled if p >= q. This rule is at the heart of log4j. It assumes that levels are ordered. For the standard levels, we have ALL < DEBUG < INFO < WARN < ERROR < FATAL < OFF.

Example - Filtering Messages using LOG Level

The Following example shows how we can filter all our DEBUG and INFO messages. This program uses of logger method setLevel(Level.X) to set a desired logging level:

This example would print all the messages except Debug and Info:

Log4jDemo.java

package com.tutorialspoint;

import org.apache.logging.log4j.Level;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

public class Log4jDemo{

   /* Get actual class name to be printed on */
   private static final Logger LOGGER = LogManager.getLogger();
   
   public static void main(String[] args) {
      LOGGER.atLevel(Level.WARN);
	   
      LOGGER.trace("Trace Message!");
      LOGGER.debug("Debug Message!");
      LOGGER.info("Info Message!");
      LOGGER.warn("Warn Message!");
      LOGGER.error("Error Message!");
      LOGGER.fatal("Fatal Message!");
   }
}

Output

When you compile and run the LogClass program, it would generate the following result −

2025-09-04T13:41:43.223410900Z main ERROR Error Message!
2025-09-04T13:41:43.227410200Z main FATAL Fatal Message!

Example - Setting Levels using Configuration File

log4j provides you configuration file based level setting which sets you free from changing the source code when you want to change the debugging level.

Following is an example configuration file which would perform the same task as we did using the log.setLevel(Level.WARN) method in the above example.

Log4j2.properties

appender.0.type = Console
appender.0.name = CONSOLE
appender.0.layout.type = PatternLayout
appender.0.layout.pattern = %p - %m%n

rootLogger.level = WARN
rootLogger.appenderRef.0.ref = CONSOLE

Let us now use our following program −

Log4jDemo.java

package com.tutorialspoint;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;

public class Log4jDemo{

   /* Get actual class name to be printed on */
   private static final Logger LOGGER = LogManager.getLogger();

   public static void main(String[] args) {
      LOGGER.trace("Trace Message!");
      LOGGER.debug("Debug Message!");
      LOGGER.info("Info Message!");
      LOGGER.warn("Warn Message!");
      LOGGER.error("Error Message!");
      LOGGER.fatal("Fatal Message!");
   }
}

Output

Now compile and run the above program and you would get following result in console −

WARN - Warn Message!
ERROR - Error Message!
FATAL - Fatal Message!

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