Logging with Log4jKAMAL METTANANDASOFTWARE ARCHITECTACCELERITE – PERSISTENT SYSTEMS@KAMALMETTANANDA

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Who am I?B.Sc. in 2004 University of Moratuwa

Masters in computer sciences 2012

10+ years of industry experience

Working as an Architect in Accelerite

Author of www.digizol.com

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AgendaWhat is logging

• Why logging• How to log

Log4j 1.2• Format (Layouts)• Handler (Appenders) • Logger (Categories)

Log4j 2

Java logging API

Learn further

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Objective

Make sure ALL brothers & sisters know how to use log4j in a Java project

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What is logging

Pile of logs in Indonesia. Photos by Rhett Butler

“Logging, or commercial logging, involves cutting trees for sale as timber or pulp”

• mongabay.com

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What is logging

“Logging refers to the recording of activity. Logging is a common issue for development teams. Several frameworks ease and standardize the process of logging for the Java platform.”

• wikipedia

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Why logging

Troubleshoot by finding

What has happened

What is happening

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What to log•Meaningful message•State of objects•Exceptions•Class name•Time of logging•Thread/invoker

Useful informati

on to troubles

hoot

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How to log

System.out.print()

• Most simplest• Not enough information• Unable to switch on/off

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How to log

Use a dedicated logging library

• A lot of required information• Simple enable/disable mechanism• Configurable without code changes• Multiple destinations

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Logging librariesLog4j v1.2

Log4j v2

JUL - Java Logging API

Logback

Commons logging

SLF4J

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Log4j 1.2APACHE SOFTWARE

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Environment SetupInstall Java

• From https://github.com/lkamal/log4j-workshop

Install Eclipse

Import Projects

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Log4j 1.2Started in 1996

• Released in around 2000

Free and Open source

• Apache Licensed – 2.0

Latest version 1.2.17

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Enabling Log4j in project

•log4j-1.2.x.jarJar file•log4j.properties OR•log4j.xml

Configuration file

•org.apache.log4j.LoggerLogger instance

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Hello World sampleHello world with Sysout

•01_helloworld_sysout

Hello world with log4j

•02_helloworld_log4j

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Log4j Components

Logger

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Logger instance by name

org.apache.log4j.Logger =

org.apache.log4j.Logger.getLogger(Class)

org.apache.log4j.Logger.getLogger(String)

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Logger Instance public class MainLog4j { private static Logger logger = Logger.getLogger(MainLog4j.class); …

}

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Simple log4j.properties file

# top level config=logging level, appenders log4j.rootLogger=INFO, console

# console appender configurations log4j.appender.console=org.apache.log4j.ConsoleAppender

log4j.appender.console.layout=org.apache.log4j.SimpleLayout

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Calculator sampleCalculator

with Sysout•03_calculator_sysout

Calculator with log4j

•04_calculator_log4j

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Log level - PriorityTRACE

ERROR

FATALLog Filter Size

Message Priority

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Log Level - UsageLeast priority messageslogger.trace()

logger.debug()

logger.info()

logger.warn()

logger.error()

Highest priority messageslogger.fatal()

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Log Level - log4j.properties

log4j.rootLogger=<LEVEL>, <Appenders>

• e.g:• DEBUG, console• INFO , console• ERROR , console

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Calculator with log levelsCalculator with

log levels

•05_calculator_log4j_levels

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log4j.properties - file content

log4j.rootLogger

Log level

Appenders

log4j.appender

Destination

Layout

log4j.logger

Package

Log Level

Appenders

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Layout - Format

log4j.appender.<appender>.layout property value

• org.apache.log4j.SimpleLayout• INFO - message

• org.apache.log4j.HTMLLayout• HTML table row per log line

• org.apache.log4j.xml.XMLLayout• XML tag per log line

• org.apache.log4j.PatternLayout• Mostly used

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Calculator with log formatting

Calculator with

xml/html logs

•06_calculator_log4j_format

Calculator with Pattern Layout logs

•07_calculator_log4j_patterlayout

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log4j.properties - file content

log4j.rootLogger

Log level

Appenders

log4j.appender

Destination

Layout

log4j.logger

Package

Log Level

Appenders

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Appenders – Output Handlers

log4j.appender.<appender> property

• A name must be given for <appender>• org.apache.log4j.ConsoleAppender

• System out / console• org.apache.log4j.FileAppender

• To a given file• org.apache.log4j.RollingFileAppender

• When one file is full – move to next• org.apache.log4j.DailyRollingFileAppender

• Daily write to a new file

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Appenders – Log Level

log4j.appender.<appender>.Threshold

• Required log level can be configured by overriding root level.• e.g.:

• log4.appender.console.Threshold=INFO

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Calculator with appenders

Calculator with

multiple log destination

s

• 08_calculator_log4j_appenders

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log4j.properties - file content

log4j.rootLogger

Log level

Appenders

log4j.appender

Destination

Layout

log4j.logger

Name

Log Level

Appenders

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Logger - Categories

log4j.logger.<logger-name> property

• Log level• Restrict the log level for the package

• Appender• Restrict the appender for the logs

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Calculator with CategoriesCalculator with

different loggers

•09_calculator_log4j_categories

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Logging Exceptions•logger.trace(msg, exception)•logger.debug(msg, exception)•logger.info(msg, exception)•logger.warn(msg, exception)•logger.error(msg, exception)•logger.fatal(msg, exception)

Exceptions can be logged

with stack trace

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Calculator with exceptionCalculator with

exception

•10_calculator_log4j_exception

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Log4j – Performance hit

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Log4j – Performance hitif (logger.isDebugEnabled()) {

logger.debug(“method invoked ” + result);

}

if (logger.isInfoEnabled()) {

logger.info(“method invoked ” + result);

}

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Log4j 1.2 SummarySupports logging by

simple on/off mechanism

required information

multiple destinations

Needs only 3 items

Library

Configuration file

Logger instances

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Log4j 2Performance improved against log4j 1.2

• Disclaimer: I am the founder of log4j, slf4j and logback projects but unaffiliated with log4j 2.0. As I understand it, notwithstanding its name, log4j 2.0 is very different than log4j 1.x. As far as the user API is concerned, log4j 2.0 is largely incompatible with log4j 1.x.• stackoverflow.com/a/12095467/2581128

Configuration via xml, not properties file

Migration tool for 1.2 to 2 available

Not by original author

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JUL - Java logging APIJava itself has a

logging API

java.util.logging.Logger

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Logging libraries

© zeroturnaround.com

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Learn furtherLogback

Log4j 2

JUL - Java logging API

Commons-logging

SLF4j

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Thank you