How to lookup property parameter in web app for log4j2?

Question

I want to configure log4j2 to lookup the logging path dynamically from web startup (tomcat).

From the docs ( http://logging.apache.org/log4j/2.x/manual/lookups.html ) there is a web: lookup with different parameter possibilities.

At first I'm trying the provided example:

<Appenders>
   <File name="ApplicationLog" fileName="${web:rootDir}/app.log"/>
</Appenders>

Result: ERROR Unable to create file ${web:rootDir}/app.log java.io.IOException

I also tried the other buildin properties like servletContextName and contextPath with the same error message.

So I'm probably still missing something important. But what?

Answer 1

For automatic replacement of the ${web:...} placeholders in your logging configuration, you need the log4j-web jar as well as log4j-core . Without the former Log4j2 will work, but it won't replace these placeholders.

Perhaps you are missing that dependency in your project?

Log4j-web on Maven Central

Answer 2

Is ${web:rootDir} a value? The placeholder is not replaced by its real value.

In the page you can red:

Information on how to use Lookups in configuration files can be found in the Property Substitution: http://logging.apache.org/log4j/2.x/manual/configuration.html#PropertySubstitution