Log4 J

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Log4J
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Introduction
Use Log4J as a standard approach to log
messages in an application.
Messages can be logged to Console, File,
Network, Database etc.
In other words you can print or store your
application messages to Console or File or
Database or other targets.
It is originally developed by IBM
Now it is Open Source

Logging – Conventional Approach
Write all messages on Console.
Console has limitations.
Application
System.out.println
(“Email is working”);

Message Level
 Logging messages can be categorized as
o Debug Message
 S.o.p(“Now inserting record …..”);
o Information Message
 S.o.p(“Email server is started”);
o Warning Message
 S.o.p(“Email server is not started, Email may get delayed”);
o Error Message
 S.o.p(“IP Exception – Shared drive not accessible”);
o Fatal Message
 S.o.p(“Database server is down”);
 Log4J gives separate methods to log different level of
messages

Log4J : Appenders
Log4J facilitates message logging on
multiple targets
o Console
o File
o Network
o FTP
o Database, etc.
An Appender is configured for each target.

Log Messages
 import org.apache.log4j.Logger;
 public class Test{
 static Logger log = Logger.getLogger(Test.class);//Create Logger
 public static void main(String[] args) {
 log.debug("This is Debug Statement");
 log.info("This is Info Statement");
 log.warn("This is Warn Statement");
 log.error("This is Error Statement");
 log.fatal("This is Fatal Statement");
o int i = 0;
o try {
 int x = 5 / i;
o } catch (RuntimeException e) {
 log.error("Arithmetic Error ",e);
o }
 }
 }

Output
 28 Jun 2007 17:35:41 DEBUG TestLog:15 - This is Debug Statement
 28 Jun 2007 17:35:41 INFO TestLog:16 - This is Info Statement
 28 Jun 2007 17:35:41 WARN TestLog:17 - This is Warn Statement
 28 Jun 2007 17:35:41 ERROR TestLog:18 - This is Error Statement
 28 Jun 2007 17:35:41 FATAL TestLog:19 - This is Fatal Statement
 28 Jun 2007 17:35:41 ERROR TestLog:26 - Arithmetic Error
 java.lang.ArithmeticException: / by zero
 at com.log4J.TestLog.main(TestLog.java:24)

Level Priorities
 Level Priorities
o debug< info< warn < error <fatal
 Logging level can be defined in the log4j.properties.
o log4j.rootLogger=debug, stdout
 Log4J will log all the messages for defined level and its high
priority level.
 For example if defined level is debug then it will log
messages for debug, info, warn and fatal.
 If defined level is warn then it will log messages for warn ,
error and fatal levels.

Configuration File
log4j.properties
XML can also be used
Keep it in root class path folder
It will configure
oAppenders
oMessage Layout
oMessage Target

Appender
An Appender is an object that sends log
messages to their final destination.
It defines message targets.
o Console
o File
o Network
o FTP
o Database
o Etc.

Console Appender

Console Appender
Log messages on Console
Configure Standard Output Appender
### direct log messages to std out ###
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{dd MMM yyyy
HH:mm:ss} %5p %c{1}:%L - %m%n
### set log category - debug,info,warn,error,fatal
log4j.rootLogger=debug,stdout

File Appender

File Appender
Log messages in a File
### direct messages to file hibernate.log ###
log4j.appender.file=org.apache.log4j.FileAppender
log4j.appender.file.File=c:/temp/corejava.log
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%d{dd MMM yyyy
HH:mm:ss} %5p %c{1}:%L - %m%n
### set log category - debug,info,warn,error,fatal
log4j.rootLogger=debug,file, stdout
Message will be sent to two appenders file and stdout

Rolling File Appender
It will roll (create) log files based on size or date or
both depending on configuration.
That means new log file will be created when
File size is full
Date is changed

Other Appenders
 SocketAppender – Dumps log output to a socket
 SyslogAppender – Write to the syslog.
 NTEventLogAppender – Write the logs to the NT Event Log
system.
 SocketAppender – Dumps log output to a socket
 SMTPAppender – Sends Messages to email
 JMSAppender – Sends messages using Java Messaging
Service
 Or create your own. Not that difficult.

Message Pattern
log4j.appender.file.layout.ConversionPattern
=%d{dd MMM yyyy HH:mm:ss} %5p %c{1}:
%L - %m%n
Used to customize the layout of a log entry.
The format is closely related to conversion
pattern of the printf function in ‘c’ language.

PatternLayout Options
 c - Used to output the category of the logging event.
 C - Used to output the fully qualified class name of the caller issuing the logging
request.
 d - Used to output the date of the logging event. The date conversion specifier
may be followed by a date format specifier enclosed between braces. For
example, %d{HH:mm:ss,SSS} or %d{dd MMM yyyy HH:mm:ss,SSS}. If no date
format specifier is given then ISO8601 format is assumed
 F - Used to output the file name where the logging request was issued.
 l - Used to output location information of the caller which generated the logging
event. (C+M+L)
 L - Used to output the line number from where the logging request was issued.

PatternLayout ( Contd.)
 n - Outputs the platform dependent line separator character or
characters.
 M - Used to output the method name where the logging request was
issued.
 p - Used to output the priority of the logging event.
 t - Used to output the name of the thread that generated the logging
event.
 x - Used to output the NDC (nested diagnostic context) associated with
the thread that generated the logging event.

Application Environments
There are different application environment
for different kind of users
Developer develops application in
development Environment
Tester tests application in QA Environment
End User accesses application from
Production Environment ( Live Server )

Development
Tomcat
MySQL
Test ( QA )
Tomcat
MySQL
Production
Tomcat
MySQL
Developer Testers End User

Development
JBoss
Oracle
Test ( QA )
JBoss
Oracle
Production
JBoss
Oracle

Development
Tomcat
Oracle
Test ( QA )
Tomcat
Production
Tomcat
DB

Environments
Development
JBoss
Oracle
Test ( QA )
JBoss
Production
JBoss
Oracle

App Env & Message Level
There are different message levels for
different application environments
o Development Environment : debug
o Test (QA) Environment : info
o Production : warn

Say NO to
System.out.println(“message”);

Say YES to
Log4J

Dependency
log4j.jar

Disclaimer
This is an educational presentation to enhance the
skill of computer science students.
This presentation is available for free to computer
science students.
Some internet images from different URLs are
used in this presentation to simplify technical
examples and correlate examples with the real
world.
We are grateful to owners of these URLs and
pictures.
www.SunilOS.com 2903/17/16

Thank You!
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03/17/16

Log4 J

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