Complete “Scala Logging” Example

Question

I'm trying to use Typesafe's Scala Logging but couldn't get it to print any debug message. I expect Scala Logging to print debug message to the default screen but it doesn't work. A complete example would be very helpful or specific advise what to change would be great too. I use Scala 2.11. Here is what I did:

1. I added the dependency to build.sbt:

   libraryDependencies += "com.typesafe.scala-logging" %% "scala-logging" % "3.1.0"
   

   Even though I'm not sure if this is required, I added the following line but it didn't do any difference:

   libraryDependencies += "com.typesafe.scala-logging" % "scala-logging-slf4j_2.11" % "2.1.2"
   

2. This is how my class looks like basically:

   import com.typesafe.scalalogging._
   
   class MyClass extends LazyLogging {
     // ...
     logger.debug("Here goes my debug message.")
     // ...
   }
   

3. I discovered the file ./src/main/resources/logback.xml but am not sure which module installed it and if its relevant. I changed the log level to "debug" without effect.

   <configuration>
   
     <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>
   
     <logger name="scala.slick" level="DEBUG"/>
   
     <root level="debug">
       <appender-ref ref="STDOUT" />
     </root>
   </configuration>
   

Answer 1

IIRC it'll print messages starting from info level by default. To change this, you need to put logback.xml file into src/main/resources (or use -Dlogback.configurationFile=/path/to/config.xml JVM parameter). See Configuration chapter in Logback documentation.

Answer 2

You're close, but you have to declare a logger instance using an SLF4J logger in the apply method for the Logger companion in com.typesafe.scalalogging. In your build.sbt include:

libraryDependencies += "com.typesafe.scala-logging" %% "scala-logging" % "3.1.0"

libraryDependencies += "org.slf4j" % "slf4j-api" % "1.7.10"

Then this will work:

import com.typesafe.scalalogging._
import org.slf4j.LoggerFactory

class MyClass extends LazyLogging {
  // ...
  val logger = Logger(LoggerFactory.getLogger(this.getClass))
  logger.debug("Here goes my debug message.")
  // ...
}

Here is a reference for LoggerFactory. Hope it helps!

Answer 3

For those who're still struggling for how to make your scala-logging work in your sbt project. They just need to follow these steps:

1. Add these two dependencies in your build.sbt:

   libraryDependencies += "com.typesafe.scala-logging" %% "scala-logging" % "3.1.0"
   libraryDependencies += "ch.qos.logback" % "logback-classic" % "1.1.2"
   

2. Create a file logback.xml in your /src/main/resources/ and paste below mentioned content in that file.

   <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>
   
       <appender name="FILE" class="ch.qos.logback.core.FileAppender">
           <!-- path to your log file, where you want to store logs -->
           <file>/Users/yourusername/test.log</file>
           <append>false</append>
           <encoder>
               <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
           </encoder>
       </appender>
   
       <root level="debug">
           <appender-ref ref="STDOUT" />
           <appender-ref ref="FILE" />
       </root>
   </configuration>
   

3. Extend your Scala class or object with trait LazyLogging:

   import com.typesafe.scalalogging.slf4j.LazyLogging
   class MyClass extends LazyLogging {
     logger.debug("This is very convenient ;-)")
   }
   

4. It's done.

P.S: Only a side note that logger is already a member of trait LazyLogging so you don't need to create it (as shown in above example)