[slf4j-dev] [Bug 291] New: Unusable with Logback-ContextSelectors.

[bugzilla-daemon at qos.ch]

http://bugzilla.slf4j.org/show_bug.cgi?id=291

           Summary: Unusable with Logback-ContextSelectors.
           Product: SLF4J
           Version: 1.7.x
          Platform: PC
        OS/Version: Windows XP
            Status: NEW
          Severity: major
          Priority: P1
         Component: log4j-over-slf4j
        AssignedTo: slf4j-dev at qos.ch
        ReportedBy: thomas.moeller at continentale.de


Log4j-Loggers are cached in static fields.

See org.apache.log4j.Log4jLoggerFactory:

  public static synchronized Logger getLogger(String name) {
    if (log4jLoggers.containsKey(name)) {
      return (org.apache.log4j.Logger) log4jLoggers.get(name);
    } else {
      Logger log4jLogger = new Logger(name);

      log4jLoggers.put(name, log4jLogger);
      return log4jLogger;
    }
  }

A Log4j-Logger caches a reference to a Slf4j-Logger.

See org.apache.log4j.Category:

Category(String name) {
    this.name = name;
    slf4jLogger = LoggerFactory.getLogger(name);
    if (slf4jLogger instanceof LocationAwareLogger) {
      locationAwareLogger = (LocationAwareLogger) slf4jLogger;
    }
  }

The problem is that the result of LoggerFactory.getLogger(name) is not
cacheable because it could depend on Logback-ContextSelectors. One example: the
JNDI-ContextSelector switches between different JNDI-Contexts. If the
log4j-over-slf4j bridge jar is installed in a shared classloader the first
request to getLogger() would tie the logger to the respective JNDI-Context.

And it is not a solution to move the bridge jar to each web application because
the context selector could switch e. g. between users.

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