log4j - Json Template Layout

If you want to encode your complete logging information in a JSON formatted file, then you can use org.apache.logging.log4j.JsonTemplateLayout to format your logging information.

JsonTemplateLayout is highly customizable, efficient layout. It is a garbage-free JSON generating layout as well. LogEvents are genereated according to the structure described by the JSON template provided in classpath.

CustomLayout.json

{
   "instant": { 
      "$resolver": "timestamp",
      "pattern": {
         "format": "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'",
         "timeZone": "UTC"
      }
   },
   "aConstant": 1, 
   "message": { 
      "$resolver": "message",
      "stringified": true
   }
}

log4j2.properties

appender.0.layout.type = JsonTemplateLayout
appender.0.layout.eventTemplateUri = classpath:CustomLayout.json

log4j2.xml

<Appenders>
   <Console name="logFile">
      <JsonTemplateLayout eventTemplateUri="classpath:CustomLayout.json"/>
</Appenders>

Example - Usage of JsonTemplateLayout

Following is a simple configuration file for JsonTemplateLayout:

log4j2.properties

# Define the appender
appender.0.type = Console
appender.0.name = CONSOLE

appender.0.layout.type = JsonTemplateLayout
appender.0.layout.eventTemplateUri = classpath:CustomLayout.json

# Define the root logger with appender Console
rootLogger.level = DEBUG
rootLogger.appenderRef.0.ref = CONSOLE

Now create a template json in current classpath:

CustomLayout.json

{
   "instant": { 
      "$resolver": "timestamp",
      "pattern": {
         "format": "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'",
         "timeZone": "UTC"
      }
   },
   "aConstant": 1, 
   "message": { 
      "$resolver": "message",
      "stringified": true
   }
}

Now consider the following Java Example which would generate logging information:

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.debug("Hello this is an debug message");
      LOGGER.info("Hello this is an info message");
   }
}

Output

Compile and run the above program. Console will print the following log information:

{"instant":"2025-09-07T14:58:18.268Z","aConstant":1,"message":"Hello this is an debug message"}
{"instant":"2025-09-07T14:58:18.273Z","aConstant":1,"message":"Hello this is an info message"}