Logback is a logging framework for Java that consists of three modules: logback-core, logback-classic, and logback-access. Logback-classic builds upon logback-core to provide logging services for most popular logging frameworks like SLF4J. It uses Loggers, Appenders, and Layouts where Loggers generate log information, Appenders write log data to destinations, and Layouts specify the format of the log output. Logback reads configuration files like logback.xml to configure loggers, appenders, and logging levels. Common appenders include ConsoleAppender for console output and FileAppender for file output.

1. Logging with Logback
in Scala
Anurag Srivastava
Software Consultant
Knoldus Software LLP

2. Agenda

Logger

Logback

Logback Architecture

Logback-classic-module

Configuration

Appenders

3. What is Loggers or Logging ?

4. Logging refers to the recording of activity.
Logging is a common issue for development
teams.

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

6. What is Logback ???

7. 
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

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

10. 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.

11. 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".

12. 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);
public void warn(String message);
public void error(String message);
}

13. 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.

15. 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.

16. 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.

17. logback.xml

18. 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.PatternLayoutEncoder by default -->
<encoder>
<pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
</encoder>
</appender>
<root level="debug">
<appender-ref ref="STDOUT" />
</root>
</configuration>

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

20. Configuration file syntax

21. 
Case sensitivity of tag names

Configuring loggers, or the <logger> element

Configuring the root logger, or the <root> element

Configuring Appenders

22. <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>

23. 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

24. 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>

25. Shouldn't log everything.

26. 
Performance will be affected.

Take a long time to analyze important
information

27. Source :

http://logback.qos.ch/manual/introduction.html