About log4j.properties

log4j.properties Syntax:
Following is the syntax of log4j.properties file for an appender X:

[sourcecode language="text"]
# Define the root logger with appender X
log4j.rootLogger = DEBUG, X

# Set the appender named X to be a File appender
log4j.appender.X=org.apache.log4j.FileAppender

# Define the layout for X appender
log4j.appender.X.layout=org.apache.log4j.PatternLayout
log4j.appender.X.layout.conversionPattern=%m%n
[/sourcecode]

log4j.rootLogger - the first element should be the logging level, Second one should be the appender

Logging levels -
TRACE < DEBUG < INFO < WARN < ERROR < FATAL < ALL

Level	Description
ALL	All levels including custom levels.
DEBUG	Designates fine-grained informational events that are most useful to debug an application.
ERROR	Designates error events that might still allow the application to continue running.
FATAL	Designates very severe error events that will presumably lead the application to abort.
INFO	Designates informational messages that highlight the progress of the application at coarse-grained level.
OFF	The highest possible rank and is intended to turn off logging.
TRACE	Designates finer-grained informational events than the DEBUG.
WARN	Designates potentially harmful situations.

We have used only one appender FileAppender in our example above. All the possible appender options are:

• AppenderSkeleton


• AsyncAppender


• ConsoleAppender


• DailyRollingFileAppender


• ExternallyRolledFileAppender


• FileAppender


• JDBCAppender


• JMSAppender


• LF5Appender


• NTEventLogAppender


• NullAppender


• RollingFileAppender


• SMTPAppender


• SocketAppender


• SocketHubAppender


• SyslogAppender


• TelnetAppender


• WriterAppender

We have used PatternLayout with our appender. All the possible options are:

• DateLayout


• HTMLLayout


• PatternLayout


• SimpleLayout


• XMLLayout

Log4j with NetBeans IDE

I think this post will help you to configure the log4j in Netbeans IDE

First you have to create the Java Project "Log4j"
Then you have to put the "log4j.properties" file in to your src folder "This should be located in root"

[sourcecode language="text"]
#### Use Three appenders,
#stdout - is used for write to console
#R - is used for write to file
log4j.rootLogger=debug, stdout, R
# Print only messages of priority WARN or higher for your category
# log4j.category.your.category.name=WARN
# Specifically inherit the priority level
#log4j.category.your.category.name=INHERITED

# Print only messages of level WARN or above in the package
#This is use for debuging mode
log4j.logger.testlogging=DEBUG

&nbsp;

#### Appender writes to console
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
# Pattern to output the caller's file name and line number.
log4j.appender.stdout.layout.ConversionPattern=%d{yyyy-MM-dd} %5p [%t] (%F:%L) - %m%n

&nbsp;

#### Appender writes to a file
#log4j.appender.R=org.apache.log4j.FileAppender
log4j.appender.R=org.apache.log4j.RollingFileAppender
log4j.appender.R.File=example.log
# Control the maximum log file size
log4j.appender.R.MaxFileSize=100KB
# Archive log files (one backup file here)
log4j.appender.R.MaxBackupIndex=1
log4j.appender.R.layout=org.apache.log4j.PatternLayout
log4j.appender.R.layout.ConversionPattern=%d{yyyy-MM-dd} %5p [%t] (%F:%L) - %m%n
#log4j.appender.R.layout.ConversionPattern=%n%p - %m
[/sourcecode]


Finally you have to take this "log4j-1.2.17.jar" file and add in to the class path

Now you done all configuration lets try to use it

[sourcecode language="java"]
package log4j;

import org.apache.log4j.Logger;

/**
*
* @author dinuka
*/
public class Log4J {

//initializing the logger
static Logger log = Logger.getLogger(Log4J.class.getName());

/**
* @param args the command line arguments
*/
public static void main(String[] args) {
//logging in different levels
log.trace("This is a Trace");
log.debug("This is a Debug");
log.info("This is an Info");
log.warn("This is a Warn");
log.error("This is an Error");
log.fatal("This is a Fatal");

}
}
[/sourcecode]

Output file

[sourcecode language="text"]
2012-09-11 TRACE [main] (Log4J.java:19) - This is a Trace
2012-09-11 DEBUG [main] (Log4J.java:20) - This is a Debug
2012-09-11 INFO [main] (Log4J.java:21) - This is an Info
2012-09-11 WARN [main] (Log4J.java:22) - This is a Warn
2012-09-11 ERROR [main] (Log4J.java:23) - This is an Error
2012-09-11 FATAL [main] (Log4J.java:24) - This is a Fatal

[/sourcecode]