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

[Tom Liu]

Hi Ceki,

I opened the bug here: http://bugzilla.slf4j.org/show_bug.cgi?id=194

Thank you very much,
Tom

On Tue, Aug 10, 2010 at 3:09 PM, Ceki Gulcu <ceki at qos.ch> wrote:
> 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
>
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