Log4j2: Markers

By using log4j2 framework, you can generate debugging and diagnostic information only when it is needed. For example, an application has two kinds of users ADMIN, GENERAL. Application wants to track ADMIN actions all the time, but it doesn’t want to track GENERAL user actions all the time. One way to accomplish this is shown below.

For example, following application define two markers one for ADMIN and other for GENERAL users.

log4j2.xml is configured like below.

<MarkerFilter marker="ADMIN" onMatch="ACCEPT" onMismatch="DENY" />

Above statement logs the events, if the marker is ADMIN, else don’t log the events.

log4j2.xml

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="DEBUG" monitorInterval="30">
 <Appenders>
  <Console name="my_console_appender" target="SYSTEM_OUT">
   <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n" />
   <MarkerFilter marker="ADMIN" onMatch="ACCEPT"
    onMismatch="DENY" />
   >
  </Console>
 </Appenders>
 <Loggers>
  <Root level="trace">
   <AppenderRef ref="my_console_appender" />
  </Root>
 </Loggers>
</Configuration>

package log4j_tutorial;

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

public class HelloWorld {
 private static final Logger logger = LogManager.getLogger();
 private static final Marker ADMIN_USER = MarkerManager.getMarker("ADMIN");
 private static final Marker GENERAL_USER = MarkerManager
   .getMarker("GENERAL");

 public static void adminActions() {
  logger.info(ADMIN_USER, "Admin actions are triggered");
 }

 public static void generalActions() {
  logger.info(GENERAL_USER, "User actions are triggered");
 }

 public static void main(String args[]) {
  adminActions();
  generalActions();
 }
}

Output

18:05:36.096 [main] INFO  log4j_tutorial.HelloWorld - Admin actions are triggered

Following are the attributes for Marker filter.

Attribute	Type	Description
marker	String	The name of the Marker to compare.
onMatch	String	Action to take when the filter matches. May be ACCEPT, DENY or NEUTRAL. The default value is NEUTRAL.
onMismatch	String	Action to take when the filter does not match. May be ACCEPT, DENY or NEUTRAL. The default value is DENY.

How can you log both ADMIN and GENERAL user actions?        

Update Marker filter like below.

<MarkerFilter marker="ADMIN" onMatch="ACCEPT" onMismatch="ACCEPT" />

                           (OR)

<MarkerFilter marker="ADMIN" onMatch="ACCEPT" onMismatch="NEUTRAL" />

                           (OR)

<MarkerFilter marker="ADMIN" onMatch="ACCEPT" onMismatch="NEUTRAL" />

<MarkerFilter marker="GENERAL" onMatch="ACCEPT" />

Above statement accept both ADMIN and GENERAL user log messages. You will get following statements in console.

18:35:26.861 [main] INFO  log4j_tutorial.HelloWorld - Admin actions are triggered

18:35:26.862 [main] INFO  log4j_tutorial.HelloWorld - User actions are triggered

private static final Marker ADMIN_USER = MarkerManager.getMarker("ADMIN");

Above statement retrieves a Marker or create a Marker that has no parent. All Markers created by MarkerManager are immutable.

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