This presentation explains introduction to logback and its components and about configuration of logback.xml file, appenders as File and SMTP.

1. Logging with Logback
in Scala
Rishi Khandelwal
Software Consultant
Knoldus Software LLP

2. Agenda

Logging

Logback

Logback Architecture

Logback-classic-module

Configuration

Variable Substitution

Appenders

3. What is Logging ?

4. Logging is the process of recording application
actions and state to a secondary interface.

5. Logging Levels

TRACE

DEBUG

INFO

WARN

ERROR

6. Don't log everything.

7. 
Excessive logging is costly.

Performance will be affected.

Take a long time to analyze important
information

8. Logback ???

9. 
Logback is intended as a successor to the popular log4j project.

Logback is divided into three modules
logback-core
logback-classic
logback-access

logback-core module lays the groundwork for the other two modules.

logback-classic natively implements the SLF4J API

logback-access module integrates with Servlet containers, such as
Tomcat and Jetty

11. Logback-classic-module

Built upon three main classes: Logger,
Appender and Layout

Logger → logback-classic

Appender & layout → logback-core

12. Logger Context

It is the logging space which is categorized according to developer-chosen
criteria.

Every single logger is attached to a LoggerContext.

It is responsible for arranging loggers in a tree like hierarchy.

Loggers are named entities which is case-sensitive.

They follow the hierarchical naming rule.

13. Named Hierarchy
A logger is said to be an ancestor of another logger if its name followed by a dot is
prefix of the descendant logger name.
A logger is said to be a parent of a child logger if there are no ancestors between
itself and the descendant logger.
"com.foo" is a parent of the logger named "com.foo.Bar".
"java" is a parent of "java.util" and an ancestor of "java.util.Vector".

14. Root Logger
The root logger resides at the top of the logger hierarchy. It is
exceptional in that it is part of every hierarchy at its inception.
Like every logger, it can be retrieved by its name, as follows:
val rootLogger = LoggerFactory.getLogger(org.slf4j.Logger.ROOT_LOGGER_NAME)
Other methods :
package org.slf4j;
public interface Logger {
// Printing methods:
public void trace(String message);
public void debug(String message);
public void info(String message);

15. Effective Level

Loggers may be assigned levels

If a given logger is not assigned a level, then it inherits one from its closest
ancestor with an assigned level

The root logger always has an assigned level. By default, this is DEBUG.
The effective level for a given logger L, is equal to the first non-null level in its
hierarchy, starting at L itself and proceeding upwards in the hierarchy
towards the root logger.

17. Basic Selection Rule
A log request of level p issued to a logger having an effective level q, is enabled if p >=
q.
levels order: TRACE < DEBUG < INFO < WARN < ERROR.

18. Configuration

Logback tries to find a file called logback.groovy in the classpath.

If no such file is found, logback tries to find a file called logback-test.xml in the
classpath.

If no such file is found, it checks for the file logback.xml in the classpath..

If neither file is found, logback configures itself automatically using the
BasicConfigurator which will cause logging output to be directed to the console.

19. logback.xml

20. Printing status messages
<configuration debug="true">
<appender name="STDOUT"
class="ch.qos.logback.core.ConsoleAppender"
>
<!-- encoders are assigned the type
ch.qos.logback.classic.encoder.PatternLayoutE
ncoder by default -->
<encoder>

21. Automatically reloading configuration file
upon modification
<configuration scan="true">
...
</configuration>
For scan periods :
<configuration scan="true" scanPeriod="30 seconds" >
...
</configuration>

22. Configuration file syntax

23. 
Case sensitivity of tag names

Configuring loggers, or the <logger> element

Configuring the root logger, or the <root> element

Configuring Appenders

24. <configuration>
<appender name="STDOUT"
class="ch.qos.logback.core.ConsoleAppender">
<encoder>
<pattern>
%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
</pattern>
</encoder>
</appender>
<logger name="com.configuration" level="INFO" />
<logger name="chapters.configuration.Foo" level="DEBUG" />
<root level="DEBUG">
<appender-ref ref="STDOUT" />
</root>
</configuration>

25. <configuration>
<appender name="FILE" class="ch.qos.logback.core.FileAppender">
<file>myApp.log</file>
<encoder>
<pattern>%date %level [%thread] %logger{10} [%file:%line] %msg%n</pattern>
</encoder>
</appender>
<appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
<encoder>
<pattern>%msg%n</pattern>
</encoder>
</appender>
<logger name="chapters.configuration">
<appender-ref ref="FILE" />
</logger>
<root level="debug">
<appender-ref ref="STDOUT" />
</root>
</configuration>

26. Variable Substitution
Simple substitution :
<configuration>
<property name="USER_HOME"
value="/home/rishi/Application/blog_projects/kn
olx/src/main/resources/log" />
<appender name="FILE"
class="ch.qos.logback.core.FileAppender">
<file>${USER_HOME}/myApp.log</file>

27. Variable Substitution
System Variable substitution :
<configuration>
<appender name="FILE"
class="ch.qos.logback.core.FileAppender">
<file>${USER_HOME}/myApp.log</file>
<encoder>
<pattern>%msg%n</pattern>
</encoder>

28. Variable Substitution
Variable substitution using a separate file :
<configuration>
<property
file="/home/rishi/Application/blog_projects/knol
x/src/main/resources/variable.properties" />
<appender name="FILE"
class="ch.qos.logback.core.FileAppender">
<file>${USER_HOME}/myApp.log</file>

29. Conditional processing
<!-- if-then form -->
<if condition="some conditional expression">
<then>
...
</then>
</if>
<!-- if-then-else form -->
<if condition="some conditional expression">
<then>
...
</then>

30. Appenders
Logback delegates the task of writing a logging event to components called
appenders Logback-core
Console Appender
OutputStreamAppender File Appender
Rolling File Appender
Time Based Size based Fixed Window

31. Console Appender
<appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
<encoder>
<pattern>%-4relative [%thread] %-5level %logger{35} - %msg %n</pattern>
</encoder>
</appender>
File Appender :
<appender name="FILE" class="ch.qos.logback.core.FileAppender">
<file>testFile.log</file>
<encoder>
<pattern>%-4relative [%thread] %-5level %logger{35} - %msg%n</pattern>
</encoder>
</appender>

32. Time base rolling :
<appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
<file>logFile.log</file>
<rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
<!-- daily rollover -->
<fileNamePattern>logFile.%d{yyyy-MM-dd}.log</fileNamePattern>
<!-- keep 30 days' worth of history -->
<maxHistory>30</maxHistory>
</rollingPolicy>

33. Fixed Window :
<rollingPolicy class="ch.qos.logback.core.rolling.FixedWindowRollingPolicy">
<fileNamePattern>tests.%i.log.zip</fileNamePattern>
<minIndex>1</minIndex>
<maxIndex>3</maxIndex>
</rollingPolicy>
<triggeringPolicy class="ch.qos.logback.core.rolling.SizeBasedTriggeringPolicy">
<maxFileSize>5MB</maxFileSize>
</triggeringPolicy>

34. Size and Time based :
<appender name="ROLLING"
class="ch.qos.logback.core.rolling.RollingFileA
ppender">
<file>mylog.txt</file>
<rollingPolicy
class="ch.qos.logback.core.rolling.TimeBased
RollingPolicy">
<!-- rollover daily -->
<fileNamePattern>mylog-%d{yyyy-MM-dd}.
%i.txt</fileNamePattern>

35. SMTP Appender :
<appender name="EMAIL"
class="ch.qos.logback.classic.net.SMTPAppender">
<smtpHost>smtp.gmail.com</smtpHost>
<smtpPort>587</smtpPort>
<STARTTLS>true</STARTTLS>
<username>USERNAMNE</username>
<password>PASSWORD</password>
<asynchronousSending>false</asynchronousSending>
<to>EMAIL_IDS</to>
<from>NAME</from>
<subject>ERROR: %logger{20} - %m</subject>
<layout class="ch.qos.logback.classic.PatternLayout">
<pattern>%date %-5level %logger - %message%n</pattern>
</layout>