Using system environment variables in log4j xml configuration

Question

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.

Teleprinter

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. – Teleprinter

Answer 1

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>

Allonym

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. – Gomorrah

Is there any work around to make this work using version 1.x? – Mediatize

${env:LOG_PATH} did not work for me. Rather ${sys:LOG_PATH} worked. – Cravens

@Gomorrah 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. – Lagging

@Lagging Quite simply, the separator between the variable name and the default value is ":-". That syntax seems to be inspired by bash variable evaluation. – Diggs

Answer 2

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

Zeldazelde

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. – Teleprinter

Answer 3

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.

Pyongyang

Answer 4

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

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

Nealey

Answer 5

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>

Vltava

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. – Teleprinter

@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. – Vltava

Answer 6

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}

Whimsey