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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
3. Logging – Conventional Approach
Write all messages on Console.
Console has limitations.
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Application
System.out.println
(“Email is working”);
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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
5. 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.
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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 }
}
}
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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)
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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.
9. Configuration File
log4j.properties
XML can also be used
Keep it in root class path folder
It will configure
oAppenders
oMessage Layout
oMessage Target
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10. 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.
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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
15. 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
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File size is full
Date is changed
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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.
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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.
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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.
20. 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 )
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25. 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
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29. 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.
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