Log4j 2 JSON Configuration Example

Apache Log4j 2 is an upgrade to Log4j 1.x that provides significant improvements over its predecessor such as performance improvement, automatic reloading of modified configuration files, java 8 lambda support and custom log levels. In addition to XML and properties files, Log4j can be configured using JSON also.

To include Log4j2 in your project, include below dependency in your project.

<dependency>
	<groupId>org.apache.logging.log4j</groupId>
	<artifactId>log4j-api</artifactId>
	<version>2.6.1</version>
</dependency>
<dependency>
	<groupId>org.apache.logging.log4j</groupId>
	<artifactId>log4j-core</artifactId>
	<version>2.6.1</version>
</dependency>

The Log4j2 uses Jackson to parse the JSON files – so let’s add it’s dependencies as well.

<dependency>
	<groupId>com.fasterxml.jackson.core</groupId>
	<artifactId>jackson-core</artifactId>
	<version>2.7.4</version>
</dependency>
<dependency>
	<groupId>com.fasterxml.jackson.core</groupId>
	<artifactId>jackson-databind</artifactId>
	<version>2.7.4</version>
</dependency>
<dependency>
	<groupId>com.fasterxml.jackson.core</groupId>
	<artifactId>jackson-annotations</artifactId>
	<version>2.7.4</version>
</dependency>

log4j2.json for logging into Console

You can use below log4j2.json file logging output into console. Please note that if no configuration file could be located then DefaultConfiguration will be used. This also causes logging output to go to the console.

{
    "configuration": {
        "status": "error",
        "name": "JSONConfigDemo",
        "packages": "com.howtodoinjava",
        "ThresholdFilter": {
            "level": "debug"
        },
        "appenders": {
            "Console": {
                "name": "STDOUT",
                "PatternLayout": {
                    "pattern": "%d [%t] %-5p %c - %m%n"
                }
            }
        },
        "loggers": {
            "root": {
                "level": "debug",
                "AppenderRef": {
                    "ref": "STDOUT"
                }
            }
        }
    }
}

log4j2.json for logging into rolling files

You can use below log4j2.json file logging output into size based rolling files.

{
   "configuration": {
      "name": "Default",
      "appenders": {
         "RollingFile": {
            "name":"File",
            "fileName":"C:/logs/howtodoinjava.log",
            "filePattern":"C:/logs/howtodoinjava-backup-%d{MM-dd-yy-HH-mm-ss}-%i.log.gz",
            "PatternLayout": {
               "pattern":"%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n"
            },
            "Policies": {
               "SizeBasedTriggeringPolicy": {
                  "size":"10 MB"
               }
            },
            "DefaultRolloverStrategy": {
               "max":"10"
            }
         }
      },
      "loggers": {
         "root": {
            "level":"debug",
            "appender-ref": {
              "ref":"File"
            }
         }
      }
   }
}

log4j2.json file location

You should put log4j2.json anywhere in application’s classpath. Log4j2 will scan all classpath locations to find out this file and then load it.

log4j2.json example

Let’s write a java class and write few log statements to verify that logs are appearing in console and log file as well.

package com.howtodoinjava.log4j2.examples;

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

public class Log4j2HelloWorldExample 
{
	private static final Logger LOGGER = LogManager.getLogger(Log4j2HelloWorldExample.class.getName());
	
	public static void main(String[] args) 
	{
		LOGGER.debug("Debug Message Logged !!!");
		LOGGER.info("Info Message Logged !!!");
		LOGGER.error("Error Message Logged !!!", new NullPointerException("NullError"));
	}
}

Now when you run the above program, you will get below logs in console.

2016-06-16 15:06:25 DEBUG Log4j2HelloWorldExample:12 - Debug Message Logged !!!
2016-06-16 15:06:25 INFO  Log4j2HelloWorldExample:13 - Info Message Logged !!!
2016-06-16 15:06:25 ERROR Log4j2HelloWorldExample:14 - Error Message Logged !!!
java.lang.NullPointerException: NullError
	at com.howtodoinjava.log4j2.examples.Log4j2HelloWorldExample.main(Log4j2HelloWorldExample.java:14) [classes/:?]

Happy Learning !!