Re: how to use log4j-to-jul with log4j-web

You are correct that log4j-to-jul routes the log4j2 API to java.util.logging. When using log4j-to-jul you cannot use ANY other log4j modules except for log4j-api. You must configure Tomcat’s logging to handle all the logging for your application. 

Ralph

> On Jun 2, 2023, at 3:13 PM, Jason Guild <[email protected]> wrote:
> 
> Hi All:
> 
> I have a web application that uses log4j (v2.20) which runs inside Tomcat 9.x on Java 8.
> 
> Currently, the WEB-INF/log4j2.xml configuration file in the application sends its output to a rolling file appender targeting a separate file on the file system, but what I'd like to do is make all log4j output go to the regular per-application log under ${catalina_base}/logs which is managed by the stock Tomcat JULI implementation.
> 
> We now have the log4j-to-jul module which can adapt log4j 2 output back to java.util.logging.
> Similar to my understanding of the purpose for log4j-to-slf4j, it seems that log4j-to-jul is meant to be used as an implementation by itself for log4j-api and without log4j-core.
> 
> The application currently uses log4j-web to get the all the essential setup for initializing log4j 2 under an application container. The log4j-web library appears to have a hard dependency on log4j-core.
> 
> After adding log4j-to-jul to the application classpath, I can see that it is recognized:
>> Multiple logging implementations found:
>> Factory: org.apache.logging.log4j.core.impl.Log4jContextFactory, Weighting: 10
>> Factory: org.apache.logging.log4j.tojul.JULLoggerContextFactory, Weighting: 20
> 
> But then the following error is reported:
>> ERROR StatusLogger LogManager returned an instance of org.apache.logging.log4j.tojul.JULLoggerContextFactory which does not implement org.apache.logging.log4j.core.impl.Log4jContextFactory. Unable to initialize Log4j.
> 
> In org.apache.logging.core.config.Configurator, line 47 there is a conditional that checks the return type of the logging implementation is-a Log4jContextFactory. The problem is then that JULLoggerContextFactory implements only LoggerContextFactory.
> 
> I'd like to keep my tomcat container as stock as possible. Particularly, continuing to use the built-in JULI per-application logging and *not* switching the entire container to use log4j as its logging implementation.
> 
> Can anyone suggest how I can use log4j-to-jul successfully for my use case?
> 
> Thanks,
> Jason
> 
> 
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