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Is it possible to reference system environment variables (as opposed to Java system properties) in a log4j xml configuration file?

I'd like to be able to do something like:

<level value="${env.LOG_LEVEL}" />

and have it get that from the system environment variables, so I can avoid having to pass in so many things with -D parameters.

Derek Lewis
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  • I just commented on the most upvoted answer and explained my reasoning. I've also just now upvoted the answer I accepted, for what it's worth. – Derek Lewis Sep 30 '15 at 20:46

6 Answers6

55

I tried to do that recently and couldn't get it to work. What I ended up doing is sending a variable at startup. So say you have an environment variable called $LOG_LEVEL:

<level value="${log_level}" />

and at startup...

java -Dlog_level=$LOG_LEVEL your_app
Einar
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    I specifically asked how to do this *without* having to set them all as -D parameters, so this doesn't answer my question at all. – Derek Lewis Sep 30 '15 at 20:46
29

This syntax is documented only in log4j 2.X so make sure you are using the correct version. It does not work on the 1.X versions.

    <Appenders>
    <File name="file" fileName="${env:LOG_PATH}">
        <PatternLayout>
            <Pattern>%d %p %c{1.} [%t] %m %ex%n</Pattern>
        </PatternLayout>
    </File>
</Appenders>
Derek Lewis
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Shoham
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    You can also specify a default using the following syntax `${env:LOG_PATH:-/default/path}` where `/default/path` will be used if `LOG_PATH` is not set. – tmortiboy Jul 25 '18 at 07:30
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    Is there any work around to make this work using version 1.x? – manikanta nvsr Apr 08 '20 at 11:07
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    ${env:LOG_PATH} did not work for me. Rather ${sys:LOG_PATH} worked. – Purushothaman Jun 17 '20 at 15:45
  • @tmortiboy i want to add a default for my env var in log4j2... what is the dash for? give a link to documentation on it. thanks. – user2052618 Jul 19 '22 at 14:21
  • @user2052618 Quite simply, the separator between the variable name and the default value is ":-". That syntax seems to be inspired by bash variable evaluation. – Chris Noe Aug 10 '23 at 17:54
12

I think this is not supported, but basically you can do two things to bring in your environment variables:

  1. Use System.setProperty before Log4J gets configured

  2. Convert (your) environment variables to system properties in your launcher

The first option basically boils down to this:

for (Map<String,String>.Entry entry : System.getenv().entrySet()) {
  System.setProperty(entry.getKey(), entry.getValue());
}

... but the question is of course where to put this code. In particular if you're running within some sort of Tomcat container or similar, this might be troublesome.

The other largely depends on your environment. Basically if you have a shell script that starts your app, you can write some shell magic to set all environment variables as properties, or just the ones you need, e.g.:

java -DMY_ENV=$MY_ENV -DMY_OTHER_ENV=$MY_OTHER_ENV -cp ... com.example.Main

It's also possible to alter your server startup scripts to support this, e.g. catalina.sh or similar.

Martin Probst
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6

You need to put a colon between env and the name of the variable, like this:

<level value="${env:LOG_LEVEL}" />
Daniel Estrada
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0

Create a system variable. I prefer to use setenv.bat for such variables.

@echo off
rem app specific log dir
set "APP_LOG_ROOTDIR=../app/app-log"
exit /b 0

Add reference in log4j.xml file

<appender name="fileAppender" class="org.apache.log4j.RollingFileAppender">
  <param name="Threshold" value="DEBUG" />
  <param name="MaxFileSize" value="512KB" />
  <param name="MaxBackupIndex" value="10" />
  <param name="File" value="${APP_LOG_ROOTDIR}/app.log"/>
  <layout class="org.apache.log4j.PatternLayout">
   <param name="ConversionPattern" value="%d %-5p %c{1} %m %n" />
  </layout>
</appender>
tkolleh
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  • Does the syntax you show there, ${APP_LOG_ROOTDIR} look at system environment variables, not just Java system properties? My understanding (and experience) has been that it only looks at Java system properties, not environment variables. – Derek Lewis Feb 04 '16 at 00:43
  • @DerekLewis Yes, the syntax looks at system environment variables. Those variables are available to tomcat at startup, similar to the variables `set` by tomcat via the _setenv.bat_ script. Note, i've only used this on windows. This isn't an issue for me on *nix so never I had to use this solution. – tkolleh Feb 04 '16 at 19:06
0

Just do this while calling the main program, it will solve the issue

  1. -DLOG4J_CONFIGURATION_FILE=P:\conf\TEST_FOLDER\ssdf\log4j2.xml -> Path from where the log4j2.xml file to be read
  2. -DLOGDIRECTORY=P:\conf\TEST_FOLDER\ssdf\Final_log_Destination\test.log -> This is the variable inputted in the xml file
  3. Use the below in the xml file for the value to get changed

${sys:LOGDIRECTORY}

Thejas HM
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