Read environment variables from logback configuration file

Question

Hi,

I have this logback.xml file:

<configuration debug="true" scan="true" scanPeriod="60 seconds">

  <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} - %msg%n</Pattern>
    </layout>
  </appender>

  <appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
    <File>${MY_HOME}/logs/mylog.log</File>

    <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
      <FileNamePattern>logs/my.%d{yyyy-MM-dd}.log</FileNamePattern>
      <MaxHistory>30</MaxHistory>
    </rollingPolicy>

    <layout class="ch.qos.logback.classic.PatternLayout">
      <Pattern>%d{HH:mm:ss.SSS} [%thread] %-5level - %msg%n</Pattern>
    </layout>

  </appender> 

  <root level="TRACE">
    <appender-ref ref="FILE"/>
  </root>

</configuration>

And ${MY_HOME} is a defined system variable (echo $MY_HOME on linux shows the correct path).

The thing is that logback doesnt seem to read it properly, it stores the logs under MY_HOME_IS_UNDEFINED/logs/my.log

What am I doing wrong? Thanks a lot!

EDIT: I made a mistake and put OSC_HOME where I really meant MY_HOME. Sorry about that

Answer 1

You perhaps mean MY_HOME. In your config file there is reference for OSC_HOME. See Variable substitution rules of Logback for details.

You can pass environment variable as a Java System property and then Logback will perform the variable substitution. You can pass this as JVM option in your command line. For example:

java -DMY_HOME=${MY_HOME} -cp ... MainClass

Or You can define MY_HOME in your config file itself.

<configuration debug="true" scan="true" scanPeriod="60 seconds">
  <property name="MY_HOME" value="/home/my" />
  <appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
    <File>${MY_HOME}/logs/mylog.log</File>
  </appender> 
</configuration>

Answer 2

Things are actually working as designed: logback doesn't read environment variables at all when doing variable substitution. Quoting the documentation:

The value of the substituted variable can be defined in the configuration file itself, in an external properties file or as a system property.

So, either use one of the mentioned solutions or get OSC_HOME_IS_UNDEFINED :)