Graylog Extended Log Format (GELF) implementation in Java and log4j appender without any dependencies.
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GELFJ - A GELF Appender for Log4j and a GELF Handler for JDK Logging


Add the following dependency section to your pom.xml:


What is GELFJ

It's very simple GELF implementation in pure Java with the Log4j appender and JDK Logging Handler. It supports chunked messages which allows you to send large log messages (stacktraces, environment variables, additional fields, etc.) to a Graylog2 server.

Following transports are supported:

  • TCP
  • UDP
  • AMQP

How to use GELFJ

Drop the latest JAR into your classpath and configure Log4j to use it.

Log4j appender

GelfAppender will use the log message as a short message and a stacktrace (if exception available) as a long message if "extractStacktrace" is true.

To use GELF Facility as appender in Log4j (XML configuration format):

<appender name="graylog2" class="org.graylog2.log.GelfAppender">
    <param name="graylogHost" value=""/>
    <param name="originHost" value=""/>
    <param name="extractStacktrace" value="true"/>
    <param name="addExtendedInformation" value="true"/>
    <param name="facility" value="gelf-java"/>
    <param name="Threshold" value="INFO"/>
    <param name="additionalFields" value="{'environment': 'DEV', 'application': 'MyAPP'}"/>

and then add it as a one of appenders:

    <priority value="INFO"/>
    <appender-ref ref="graylog2"/>

Or, in the format:

# Define the graylog2 destination
log4j.appender.graylog2.additionalFields={'environment': 'DEV', 'application': 'MyAPP'}

# Send all INFO logs to graylog2
log4j.rootLogger=INFO, graylog2

AMQP Configuration:

log4j.appender.graylog2.layout.ConversionPattern=%d{HH:mm:ss,SSS} %-5p [%t] [%c{1}] - %m%n
log4j.appender.graylog2.additionalFields={'environment': 'DEV', 'application': 'MyAPP'}


GelfAppender supports the following options:

  • graylogHost: Graylog2 server where it will send the GELF messages; to use TCP instead of UDP, prefix with tcp:
  • graylogPort: Port on which the Graylog2 server is listening; default 12201 (optional)
  • originHost: Name of the originating host; defaults to the local hostname (optional)
  • extractStacktrace (true/false): Add stacktraces to the GELF message; default false (optional)
  • addExtendedInformation (true/false): Add extended information like Log4j's NDC/MDC; default false (optional)
  • includeLocation (true/false): Include caller file name and line number. Log4j documentation warns that generating caller location information is extremely slow and should be avoided unless execution speed is not an issue; default true (optional)
  • facility: Facility which to use in the GELF message; default "gelf-java"
  • amqpURI: AMQP URI (required when using AMQP integration)
  • amqpExchangeName: AMQP Exchange name - should be the same as setup in graylog2-radio (required when using AMQP integration)
  • amqpRoutingKey: AMQP Routing key - should be the same as setup in graylog2-radio (required when using AMQP integration)
  • amqpMaxRetries: Retries count; default value 0 (optional)

Automatically populating fields from a JSON message

GelfJsonAppender is also available at org.graylog2.log.GelfJsonAppender. This appender is exactly the same as GelfAppender except that if you give it a parseable JSON string in the log4j message, then it will automatically set additional fields according to that JSON.

For example, given the log4j message "{\"simpleProperty\":\"hello gelf\"}", the GelfJsonAppender will automatically add the additional field simpleProperty to your GELF logging. These fields are in addition to everything else.

The GelfJsonAppender is fail safe. If the given log4j message cannot be parsed as JSON, then the message will still be logged, but there will be no additional fields derived from the message.

Logging Handler

Configured via properties as a standard Handler like

handlers = org.graylog2.logging.GelfHandler

.level = ALL

org.graylog2.logging.GelfHandler.level = ALL
org.graylog2.logging.GelfHandler.graylogHost =
#org.graylog2.logging.GelfHandler.graylogPort = 12201
#org.graylog2.logging.GelfHandler.extractStacktrace = true
#org.graylog2.logging.GelfHandler.additionalField.0 = foo=bah
#org.graylog2.logging.GelfHandler.additionalField.1 = foo2=bah2
#org.graylog2.logging.GelfHandler.facility = local0


What is GELF

The Graylog Extended Log Format (GELF) avoids the shortcomings of classic plain syslog:

  • Limited to length of 1024 byte
  • Not much space for payloads like stacktraces
  • Unstructured. You can only build a long message string and define priority, severity etc.

You can get more information here: