Best way to write custom json messages using log4j2

Question

I have been using log4j for different kind of projects and have some experience with log4j2. All implementations used the default appender and layout. Currently i need to write a application which writes in json format. So i tried the log4j2 JSONLayout layout by setting up a very simple log4j2 logger.

public class JSONLogger {

    private static final Logger LOGGER = LogManager.getLogger();

    public static void main(String[] args) {
        JSONLogger jsonlogger = new JSONLogger() ;
    }

    public JSONLogger() {
        LOGGER.log(Level.FATAL, "hi mum!") ;

         int val1 = 10, val2 = 11, val3 = 12;

         LOGGER.log(Level.FATAL,"val1={}, val2={}, val3={}", val1, val2, val3);
    }

}

jsonLoggerProperties.xml

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="DEBUG">
    <Properties>
        <Property name="log-path">/Users/petervannes/NetBeansProjects/JSONLogger/logfiles</Property>
    </Properties>

    <Appenders>
        <RollingFile name="json_file_appender" fileName="${log-path}/jsonlogger.json"
                     filePattern="${log-path}/%d{yyyyMMdd}_jsonlogger-%i.json" >
            <JSONLayout complete="true" compact="false"/>
            <Policies>
                <SizeBasedTriggeringPolicy size="1 KB" />
            </Policies>
            <DefaultRolloverStrategy max="4"/>
        </RollingFile>

    </Appenders>


    <Loggers>
        <root level="debug" additivity="false">
            <AppenderRef ref="json_file_appender"/>
        </root>
    </Loggers>
</Configuration>

Resulting in an log entry similar to;

, {
  "timeMillis" : 1474573600359,
  "thread" : "main",
  "level" : "FATAL",
  "loggerName" : "JSONLogger",
  "message" : "val1=10, val2=11, val3=12",
  "contextStack" : [ "fieldName2" ],
  "endOfBatch" : false,
  "loggerFqcn" : "org.apache.logging.log4j.spi.AbstractLogger",
  "threadId" : 1,
  "threadPriority" : 5
}

What i need is to log to a JSON format like this;

, {
  "DateTime" : "08/01/2016 21:33:22.334",
  "level" : "FATAL",
  "Summary" : "Something has gone wrong",
  "ChainManager" : "Manager A",
  "Optionals" : { "Key_1": "Value1",
                  "Key_2": "Value2" }
}

Is this possibile with the log4j2 JSONLayout or is there any other layout i can use to get this format ?

Answer 1

The question is about writing a custom json messages using log4j2.

This is possible since version 2.11 of log4j2 version:

https://issues.apache.org/jira/browse/LOG4J2-2190

The new parameter of for JSONLayout is called

objectMessageAsJsonObject

. Sample project files;

log4j2.properties

status = error


appender.ana_whitespace.type = RollingFile
appender.ana_whitespace.name = ana_whitespace
appender.ana_whitespace.fileName = ${sys:es.logs.base_path:-target}${sys:file.separator}ana_whitespace.log
appender.ana_whitespace.layout.type = JsonLayout
appender.ana_whitespace.layout.propertiesAsList = false
appender.ana_whitespace.layout.compact = false
appender.ana_whitespace.layout.eventEol = true
appender.ana_whitespace.layout.objectMessageAsJsonObject = true
appender.ana_whitespace.layout.complete= true
appender.ana_whitespace.layout.properties= true
appender.ana_whitespace.filePattern = ${sys:es.logs.base_path:-target}${sys:file.separator}ana_whitespace-%d{yyyy-MM-dd}.log
appender.ana_whitespace.filter.1.type = MarkerFilter
appender.ana_whitespace.filter.1.onMismatch=DENY
appender.ana_whitespace.filter.1.onMatch=ACCEPT
appender.ana_whitespace.filter.1.marker=ANA_WHITESPACE
appender.ana_whitespace.policies.type = Policies
appender.ana_whitespace.policies.time.type = TimeBasedTriggeringPolicy
appender.ana_whitespace.policies.time.interval = 1
appender.ana_whitespace.policies.time.modulate = true
appender.ana_whitespace.policies.size.type = SizeBasedTriggeringPolicy
appender.ana_whitespace.policies.size.size = 10 MB

rootLogger.level = info
rootLogger.appenderRef.ana_whitespace.ref = ana_whitespace

Example Java code

package de.es.stemmer;

import java.io.IOException;
import java.util.Map;
import java.util.TreeMap;

import org.apache.http.client.ClientProtocolException;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.Marker;
import org.apache.logging.log4j.MarkerManager;
import org.apache.logging.log4j.ThreadContext;
import org.apache.logging.log4j.core.LoggerContext;
import org.apache.logging.log4j.message.ObjectMessage;

public class JsonLoggerTest {
    final static Logger log = LogManager.getLogger(JsonLoggerTest.class);
    final static Marker MARKER_WHITESPACE = MarkerManager.getMarker("ANA_WHITESPACE");

    public static void main(String[] args) throws ClientProtocolException, IOException {
        System.setProperty("es.logs.base_path", "target");
        System.setProperty("es.logs.cluster_name", "_cluster");
        LoggerContext.getContext().reconfigure();
        ThreadContext.put("orig", "MDC_origValue");
        ThreadContext.put("source", "MDC_sourceSnippet");
        Map<String, String> map = new TreeMap<>();
        map.put("orig", "msg_origValue");
        map.put("source", "msg_sourceSnippet");
        ObjectMessage msg = new ObjectMessage(map);
        log.info(MARKER_WHITESPACE, msg);
        ThreadContext.remove("orig");
        ThreadContext.remove("source");
    }

}

JSON Log Entry

[
{
  "thread" : "main",
  "level" : "INFO",
  "loggerName" : "de.es.stemmer.JsonLoggerTest",
  "marker" : {
    "name" : "ANA_WHITESPACE"
  },
  "message" : {
    "orig" : "msg_origValue",
    "source" : "msg_sourceSnippet"
  },
  "endOfBatch" : false,
  "loggerFqcn" : "org.apache.logging.log4j.spi.AbstractLogger",
  "instant" : {
    "epochSecond" : 1526576578,
    "nanoOfSecond" : 184000000
  },
  "contextMap" : {
    "orig" : "MDC_origValue",
    "source" : "MDC_sourceSnippet"
  },
  "threadId" : 1,
  "threadPriority" : 5
}

]

Answer 2

I know this is an old question but I think there is a better way to do it.

You should use the JSON Template Layout.

And then you will be able to configure your JsonLayout with a template like this one:

{
  "mdc": {
    "$resolver": "mdc"
  },
  "exception": {
    "exception_class": {
      "$resolver": "exception",
      "field": "className"
    },
    "exception_message": {
      "$resolver": "exception",
      "field": "message"
    },
    "stacktrace": {
      "$resolver": "exception",
      "field": "stackTrace",
      "stackTrace": {
        "stringified": true
      }
    }
  },
  "line_number": {
    "$resolver": "source",
    "field": "lineNumber"
  },
  "class": {
    "$resolver": "source",
    "field": "className"
  },
  "@version": 1,
  "source_host": "${hostName}",
  "message": {
    "$resolver": "message",
    "stringified": true
  },
  "thread_name": {
    "$resolver": "thread",
    "field": "name"
  },
  "@timestamp": {
    "$resolver": "timestamp"
  },
  "level": {
    "$resolver": "level",
    "field": "name"
  },
  "file": {
    "$resolver": "source",
    "field": "fileName"
  },
  "method": {
    "$resolver": "source",
    "field": "methodName"
  },
  "logger_name": {
    "$resolver": "logger",
    "field": "name"
  }
}

There are many configurations available using templates.

See more about it here:

https://logging.apache.org/log4j/2.x/manual/json-template-layout.html