How to enable debug in slf4j Logger?

Question

How to globally enable debug for all the slf4j.Logger objects?

Answer 1

Here's a sample configuration I usually use to setup logging with logback.
Gradle dependencies (the same apply to Maven)

compile group: 'org.slf4j', name: 'slf4j-api', version: '1.7.25'
compile group: 'ch.qos.logback', name: 'logback-classic', version: '1.2.3'

logback.xml configuration to be placed in the project's classpath (src/main/resources)

<configuration>

    <statusListener class="ch.qos.logback.core.status.NopStatusListener" />

    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
        <layout class="ch.qos.logback.classic.PatternLayout">
            <Pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36}.%M\(%line\) - %msg%n</Pattern>
        </layout>
    </appender>
    
    <!-- enable debug only on org.hibernate.SQL package -->
    <logger name="org.hibernate.SQL" level="debug" additivity="false">
        <appender-ref ref="STDOUT" />
    </logger>

    <root level="info">
        <appender-ref ref="STDOUT" />
    </root>

</configuration>

Answer 2

For log4j

<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/" debug="true">

<!-- ============================== -->
<!-- Append messages to the console -->
<!-- ============================== -->

<appender name="CONSOLE" class="org.apache.log4j.ConsoleAppender">
    <param name="Target" value="System.out"/>
    <param name="Threshold" value="INFO"/>

    <layout class="org.apache.log4j.PatternLayout">
        <!-- The default pattern: Date Priority [Category] Message\n -->
        <param name="ConversionPattern" value="%d [%t] %-5p %c - %m%n"/>
    </layout>
</appender>

<appender name="web" class="org.apache.log4j.DailyRollingFileAppender">
    <param name="Threshold" value="DEBUG"/>
    <param name="Append" value="true"/>
    <param name="File" value="${catalina.home}/logs/web.log"/>
    <layout class="org.apache.log4j.PatternLayout">
        <param name="ConversionPattern" value="%d [%t] %-5p %c - %m%n"/>
    </layout>
</appender>

<category name="com.idc.scd" additivity="false">
    <priority value="${log4j.category.com.mypackage}"/>
    <appender-ref ref="web"/>
</category>

</log4j:configuration>

by this cofiguration your all "com.mypackage" logs will be written in "web.log" file under catalina.home.

Answer 3

depends on what binding you are using... if e.g. it's log4j have a look at http://logging.apache.org/log4j/1.2/manual.html and its Configuration chapter

Answer 4

exists various capability to switch debug log on:
this article have good explanation all of those. to me good fit is:

Using slf4j with Log4j logger
create file src/main/resources/log4j.properties

log4j.rootLogger=DEBUG, STDOUT
log4j.logger.deng=INFO
log4j.appender.STDOUT=org.apache.log4j.ConsoleAppender
log4j.appender.STDOUT.layout=org.apache.log4j.PatternLayout
log4j.appender.STDOUT.layout.ConversionPattern=%5p [%t] (%F:%L) - %m%n

Answer 5

Use logback as the slf4j binding.

The default behaviour without an configuration file is to log all events at level DEBUG and above to System.out. See http://logback.qos.ch/manual/configuration.html#automaticConf for details.

Answer 6

Pass the System Property -Dorg.slf4j.simpleLogger.defaultLogLevel=DEBUG at your Java startup for the SLF4J Simple api