Logging levels in log4j

Logging levels:

All logging levels are defined in the org.apache.log4j.Level class. We can also create our own levels.

Logging levels are given below:

1. ALL: All levels including custom levels also.

2. DEBUG: It helps developers in application debugging.

3. INFO: It gives the information about the progress of application and its states.

4. WARN: It gives warning for unexpected events.

5. ERROR: It provides the information about error events.

6. FATAL: It provides the information about application abort.

7. OFF: It turns off all the logging. It is opposite to the ALL level.

Standard order of all logging levels:

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

i.e. If logging level set to FATAL then only FATAL messages will be displayed, if logging level set to ERROR then ERROR and FATAL messages will be displayed and so on.

In the below example as we set the logging level to WARN so only WARN, ERROR and FATAL messages will be displayed. The DEBUG and INFO message will not display.

Example:

Log4jTest.java

import org.apache.log4j.BasicConfigurator;
import org.apache.log4j.Level;
import org.apache.log4j.Logger;
 
/**
 * This class is used to show the use of 
 * logging levels in Log4j with the BasicConfigurator.
 * @author w3spoint
 */
public class Log4jTest {
	//Get the Logger object.
	private static Logger log = Logger.getLogger(Log4jTest.class);
 
	public static void main(String[] args) {
		//Configuring Log4j, It will log all messages on console.
		//BasicConfigurator use ConsoleAppender and PatternLayout 
		//for all loggers.
		BasicConfigurator.configure();
 
		//Set logging level
		log.setLevel(Level.WARN);
 
		//logger messages
		log.debug("Log4j debug message test.");
		log.info("Log4j info message test.");
		log.warn("Log4j warn message test.");
		log.error("Log4j error message test.");
		log.fatal("Log4j fatal message test.");
	}
}

Output:

0 [main] WARN com.w3spoint.business.Log4jTest 
 - Log4j warn message test.
1 [main] ERROR com.w3spoint.business.Log4jTest 
 - Log4j error message test.
1 [main] FATAL com.w3spoint.business.Log4jTest 
 - Log4j fatal message test.

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