[slf4j-user] log4j-over-slf4j checks circular dependency too strict

[Ceki Gulcu]

Hi Tom,

Sounds reasonable. Would you open a bug report requesting the change you 
describe? Thanks,

On 10.08.2010 06:38, Tom Liu wrote:
> Hi guys,
>
> I think log4j-over-slf4j (as well as jcl bridges) checks circular
> dependency too strict.
> Even when slf4j-log4j12.jar is visible, it does not necessarily mean
> it will be picked up by slf4j-api as the logging backend.
>
> Here is a setup in tomcat 6 demonstrate the issue:
> tomcat container lib contains: jcl-over-slf4j.jar, slf4j-api.jar,
> slf4j-log4j12.jar, log4j.jar
> Webapp WEB-INF/lib contains: log4j.jar, log4j-over-slf4j.jar,
> slf4j-api.jar, logback-core.jar, logback-access.jar.
> What we want to achieve is that tomcat logging (from commons-logging)
> will be routed to log4j and webapp's logging (from log4j) will be
> routed to logback.
> In theory, there will be no circular dependencies in runtime as
> logback is picked up as the logging backend. However, webapp failed to
> start because the "potential" circular dependency is detected.
>
> Is it possible to change the circular dependency detection algorithm
> to test against the actual binding picked up? I did a hack on
> org.apache.log4j.Log4jLoggerFactory which works for me:
> class Log4jLoggerFactory {
> ...
>
> static {
>
>          LoggerFactoryBinder binder = StaticLoggerBinder.getSingleton();
>          if ("org.slf4j.impl.Log4jLoggerFactory".equals(binder.getLoggerFactoryClassStr()))
> {
>              String part1 = "Detected both log4j-over-slf4j.jar AND
> slf4j-log4j12.jar on the class path, preempting StackOverflowError.
> REPLACED ";
>              String part2 = "See also " + LOG4J_DELEGATION_LOOP_URL + "
> for more details.";
>
>              Util.reportFailure(part1);
>              Util.reportFailure(part2);
>              throw new IllegalStateException(part1 + part2);
>          }
>
>      }
> ...
>
> }
>
> Thanks,
> Tom