[FIXED] How to lookup property parameter in web app for log4j2?

Issue

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?

Solution

Add log4j-web JAR

Your usual log4j-core JAR file on its own is not enough.

There is an additional component called log4j-web.

For automatic replacement of the ${web:...} placeholders in your logging configuration, you need the additional log4j-web JAR file. If you don't have this log4j-web JAR file, then Log4j2 itself will still work, but it will not replace these placeholders with anything. So for example ${web:rootDir} will just end up as the literal text ${web:rootDir}.

Perhaps you are missing that dependency in your project?

Log4j-web on Maven Central

Answered By - JeroenHoek