Support using another slf4j backend than logback

We are using gatling 2.2.5 as part of our maven build process, and as such, it does inheritance all the libraries our product uses : slf4j, log4j1.x, log4j2.x ( i know, i know , but it’s a legacy product can’t be changed ).

The usage of logback inside gatling conflicts with these libraries, as there’s a race condition between them, so we’re giving an error :

SLF4J: Found binding in [jar:file:/D:/Users/OU83MP/.m2/repository/org/apache/logging/log4j/log4j-slf4j-impl/2.2/log4j-slf4j-impl-2.2.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/D:/Users/OU83MP/.m2/repository/org/slf4j/slf4j-log4j12/1.7.5/slf4j-log4j12-1.7.5.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/D:/Users/OU83MP/.m2/repository/ch/qos/logback/logback-classic/1.1.7/logback-classic-1.1.7.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
SLF4J: Actual binding is of type [org.apache.logging.slf4j.Log4jLoggerFactory]
15:08:00.845 [main] TRACE io.gatling.app.Gatling$ - Starting
15:08:00.942 [main] TRACE io.gatling.app.Gatling$ - Configuration loaded
15:08:01.251 [GatlingSystem-akka.actor.default-dispatcher-4] INFO  akka.event.slf4j.Slf4jLogger - Slf4jLogger started
15:08:01.251 [main] TRACE io.gatling.app.Gatling$ - ActorSystem instantiated
15:08:01.266 [main] TRACE io.gatling.app.Gatling$ - Runner instantiated
15:08:01.358 [main] TRACE io.gatling.app.Runner - Running
java.lang.reflect.InvocationTargetException
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at io.gatling.mojo.MainWithArgsInFile.runMain(MainWithArgsInFile.java:50)
        at io.gatling.mojo.MainWithArgsInFile.main(MainWithArgsInFile.java:33)
Caused by: java.lang.ClassCastException: org.apache.logging.slf4j.Log4jLoggerFactory cannot be cast to ch.qos.logback.classic.LoggerContext

If we exclude the logback dependency, we get a ClassNotFoundException. If we exclude the slf4j/log4j2 dependencies, problem still persists.

Would’nt it be better to use the slf4j-api inside gatling, and not impose the ( great ) logback impl ?

[testphreak]

Hi @slandelle I am fine with gatling shipping with Logback like before. I was in fact suggesting that above.

Could you please revert @sebastianvoss’s change to this line and catch the ClassNotFoundException instead? That would resolve this issue.

I can send a pull request if you prefer that with the change below.

finally {
    try {
      LoggerFactory.getILoggerFactory.asInstanceOf[LoggerContext].stop()
    } catch {
      case e: ClassNotFoundException => logger.info(e.getMessage)
    }
}

Catching the exception would really help the logs look clean. Also since it appears that log4j2 doesn’t have a stop method, the new warning message is not accurate. Thank you.

[sebastianvoss]

@testphreak Sorry, got distracted by some other stuff. Will do so by end of today.