Log4j
(Short introduction to log4j)
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Usage in Source Code
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Get Logger
* Logger.getRootLogger()|Logger.getLogger(String loggerName)

Print Methods:
* public void debug(Object message);    // 7
* public void info(Object message);    // 6
* public void warn(Object message);    // 4
* public void error(Object message);    // 3
* public void fatal(Object message);    // 0
* public void log(Level,Object message);  // generic print method
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Configure File
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Logger
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log4j.rootLogger = [Level], appenderName, appenderName,…
Level = OFF, FATAL, ERROR, WARN, INFO, DEBUG, ALL

Appender
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Type of Appender
* Console, Files, GUI components, Remote socket servers, JMS, NT Event Loggers, Remote UNIX Syslog daemons
–org.apache.log4j.ConsoleAppender
–org.apache.log4j.FileAppender   (Attributes: File = filename, MaxFileSize = filesize, MaxBackupIndex =1 )
–org.apache.log4j.DailyRollingFileAppender
–org.apache.log4j.RollingFileAppender
–org.apache.log4j.WriterAppender

Syntax
* log4j.appender.appenderName = fully.qualified.name.of.appender.class
* log4j.appender.appenderName.option = value

Layout
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PatternLayout    (Layout whose style can be customized)
HTMLLayout    (HTML format log)
SimpleLayout    (Just privilege and log message)
TTCCLayout    (Time, Thread, Category, …)

Syntax
* log4j.appender.appenderName.layout = fully.qualified.name.of.layout.class
* log4j.appender.appenderName.layout.option = value
* log4j.appender.appenderName.layout.ConversionPattern =