Configuring pax-logging in OSGi environment built with Gradle and BND

I am trying to get Log4J2 working via Pax Logging but online docs focus on Log4J (v1). My project is Java, Gradle with BND plugin for OSGi bundles aimed at the Equinox environment.

I am using Gradle 6.8.3

I have my build.gradle file for an OSGi bundle that aims to expose logging functionality to other bundles using:

implementation 'org.ops4j.pax.logging:pax-logging-api:2.1.0'
implementation 'org.ops4j.pax.logging:pax-logging-log4j2:2.1.0'

In my BND file, I include the following imports:

Import-Package: org.apache.logging.log4j;version="2.17.1";provider=paxlogging, org.apache.commons.logging;version="[1.1.1,2)";provider=paxlogging, org.apache.logging.log4j.core;version="2.17.1";provider=paxlogging

Since my project has file appenders defined, which don’t form part of the Log4J2 API, but Log4J2 Core, I therefore export the following from the same bundle to enable Log4J2 Core classes to have visibility in other bundles that depend on the logging bundle:

Export-Package: com.mycompany.loggingbundle, org.apache.logging.log4j, org.apache.logging.log4j.message, org.apache.logging.log4j.util, org.apache.logging.log4j.core;version="2.17.1", org.apache.logging.log4j.core.appender;version="2.17.1", org.apache.logging.log4j.core.filter;version="2.17.1", org.apache.logging.log4j.core.impl;version="2.17.1", org.apache.logging.log4j.spi;version="2.17.1"

Everything compiles, builds and install fine.

At runtime, I have an issue:

org.osgi.framework.BundleException: Could not resolve module: com.mycompany.otherbundle [1306]
  Unresolved requirement: Require-Bundle: com.mycompany.loggingbundle
    -> Bundle-SymbolicName: com.mycompany.loggingbundle; bundle-version="<hidden>"; singleton:="true"
       com.mycompany.loggingbundle [1311]
         Unresolved requirement: Import-Package: org.apache.logging.log4j.core; provider="paxlogging"; version="2.17.1"

    at org.eclipse.osgi.container.Module.start(Module.java:434)
    at org.eclipse.osgi.container.ModuleContainer$ContainerStartLevel.incStartLevel(ModuleContainer.java:1582)
    at org.eclipse.osgi.container.ModuleContainer$ContainerStartLevel.incStartLevel(ModuleContainer.java:1561)
    at org.eclipse.osgi.container.ModuleContainer$ContainerStartLevel.doContainerStartLevel(ModuleContainer.java:1533)
    at org.eclipse.osgi.container.ModuleContainer$ContainerStartLevel.dispatchEvent(ModuleContainer.java:1476)
    at org.eclipse.osgi.container.ModuleContainer$ContainerStartLevel.dispatchEvent(ModuleContainer.java:1)
    at org.eclipse.osgi.framework.eventmgr.EventManager.dispatchEvent(EventManager.java:230)
    at org.eclipse.osgi.framework.eventmgr.EventManager$EventThread.run(EventManager.java:340)

Hopefully some OSGi expert knows what I’ve got wrong because the whole reason to use Pax Logging was to avoid the need to create Log4J2 fragments and have an easier configuration for a multi-bundled environment. Perhaps there is a systematic series of things to look at to resolve this?

Answer

Update

I opened up the pax-logging-log4j2 JAR file to review its manifest and can see it doesn’t export anything from org.apache.logging.log4j.core so my re-exporting it from my bundle could never provide the core packages I was hoping.

This still leaves the problem of how to get access to things like a FileAppnder elsewhere in code, but it answers the question as to what is wrong with my approach.

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