logging with logback in scala

Logging with Logback in Scala

Rishi Khandelwal Software Consultant Knoldus Software LLP

Agenda

Logging Logback Logback Architecture Logback-classic-module Configuration Variable Substitution Appenders

What is Logging ?

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

Logging Levels

TRACE DEBUG INFO WARN ERROR

Don't log everything.

Excessive logging is costly.

Performance will be affected.

Take a long time to analyze important information

Logback ???

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

Logback is divided into three moduleslogback-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 LoggerThe 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 RuleA 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

<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>

Automatically reloading configuration file upon modification

<configuration scan="true">

...

</configuration>

For scan periods :

<configuration scan="true" scanPeriod="30 seconds" >

...

</configuration>

Configuration file syntax

Case sensitivity of tag names

Configuring loggers, or the <logger> element

Configuring the root logger, or the <root> element

Configuring Appenders

<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>

<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>

Variable Substitution

Simple substitution :

<configuration>

<property name="USER_HOME" value="/home/rishi/Application/blog_projects/knolx/src/main/resources/log" />

<appender name="FILE" class="ch.qos.logback.core.FileAppender">

<file>${USER_HOME}/myApp.log</file>

<encoder>

<pattern>%msg%n</pattern>

</encoder>

</appender>

<root level="debug">

<appender-ref ref="FILE" />

</root>

</configuration>

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>

</appender>

<root level="debug">

<appender-ref ref="FILE" />

</root>

</configuration>

sbt -DUSER_HOME="/home/rishi/Application/blog_projects/knolx/src/main/resources/log" run

Variable Substitution

Variable substitution using a separate file :

<configuration>

<property file="/home/rishi/Application/blog_projects/knolx/src/main/resources/variable.properties" />

<appender name="FILE" class="ch.qos.logback.core.FileAppender">

<file>${USER_HOME}/myApp.log</file>

<encoder>

<pattern>%msg%n</pattern>

</encoder>

</appender>

<root level="debug">

<appender-ref ref="FILE" />

</root>

</configuration>

Conditional processing <!-- if-then form -->

<if condition="some conditional expression">

<then>

...

</then>

</if>

<!-- if-then-else form -->

<if condition="some conditional expression">

<then>

...

</then>

<else>

...

</else>

</if>

Conditional processing requires the Janino library.

"org.codehaus.janino" % "janino" % "2.6.1"

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

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>

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>

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>

Size and Time based :

<appender name="ROLLING" class="ch.qos.logback.core.rolling.RollingFileAppender">

<file>mylog.txt</file>

<rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">

<!-- rollover daily -->

<fileNamePattern>mylog-%d{yyyy-MM-dd}.%i.txt</fileNamePattern>

<timeBasedFileNamingAndTriggeringPolicy

class="ch.qos.logback.core.rolling.SizeAndTimeBasedFNATP">

<!-- or whenever the file size reaches 100MB -->

<maxFileSize>100MB</maxFileSize>

</timeBasedFileNamingAndTriggeringPolicy>

</rollingPolicy>

<encoder>

<pattern>%msg%n</pattern>

</encoder>

</appender>

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>

</appender>

<root level="info">

<appender-ref ref="CONSOLE" />

<appender-ref ref="EMAIL" />

</root>