Log4j MQTT appender

Usage:

# output messages into a rolling log file as well as stdout
log4j.rootLogger=stdout,MQTT

# stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p %d{HH:mm:ss,SSS} %m%n

# MQTT
log4j.appender.MQTT=uk.co.appembassy.log4mqtt.MqttAppender
log4j.appender.MQTT.topic=logging/topic
#log4j.appender.MQTT.username=username
#log4j.appender.MQTT.password=password
log4j.appender.MQTT.broker=tcp://localhost:1883
log4j.appender.MQTT.clientid=clientid{ip}{hostname}
# the setting below defaults to json
log4j.appender.MQTT.outputFormat=[json|xml]

Client ID may contain two special values: {id} and {hostname}. If the ID is cassandra-{ip} and appender is working on 127.0.0.1, the ID will become cassandra-127.0.0.1. Alternatively {hostname} can be used.

Feedback

Any ideas? Improvements?