PowerPoint Presentation

Logging with Logback
in Scala

Anurag Srivastava Software Consultant Knoldus Software LLP

Agenda

Logger

Logback

Logback Architecture

Logback-classic-module

Configuration

Appenders

What is Loggers or Logging ?

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

Logging Levels

TRACE

DEBUG

INFO

WARN

ERROR

What is Logback ???

Logback is intended as a successor to the popular log4j project.

Logback is divided into three modules

logback-corelogback-classiclogback-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

Logback-classic-module

Built upon three main classes: Logger, Appender and Layout

Logger logback-classic

Appender & layout logback-core

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.

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".

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); }

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.

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.

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.

logback.xml

Printing status messages

%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n

Automatically reloading configuration file upon modification

...

For scan periods :

...

Configuration file syntax

Case sensitivity of tag names

Configuring loggers, or the element

Configuring the root logger, or the element

Configuring Appenders

%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n

Appenders

Logback delegates the task of writing a logging event to components called appenders Logback-core Console AppenderOutputStreamAppender File Appender

Rolling File Appender

Time Based Size based Fixed Window

Console Appender

%-4relative [%thread] %-5level %logger{35} - %msg %n

File Appender :

testFile.log %-4relative [%thread] %-5level %logger{35} - %msg%n

Shouldn't log everything.

Performance will be affected.

Take a long time to analyze important information

Source :

http://logback.qos.ch/manual/introduction.html