我工程里配的log4j.xml文件，但是由于想动态改变日志级别，所以引了logback-classic包，结果一直打印debug日志。

LoggerContext loggerContext= (LoggerContext) LoggerFactory.getILoggerFactory();
<dependency>
     <groupId>ch.qos.logback</groupId>
     <artifactId>logback-classic</artifactId>
 </dependency>

后来又加了这个依赖，放在logback-classic上面

<dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-log4j12</artifactId>
</dependency>

2018-08-13 20:43:48.478:INFO::No Transaction manager found - if your webapp requires one, please configure one.
log4j:WARN No appenders could be found for logger (org.jboss.logging).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
2018-08-13 20:43:48.922:INFO:/:Initializing Spring root WebApplicationContext
SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/D:/m2space/repository/org/slf4j/slf4j-log4j12/1.7.21/slf4j-log4j12-1.7.21.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/D:/m2space/repository/ch/qos/logback/logback-classic/1.2.0/logback-classic-1.2.0.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.slf4j.impl.Log4jLoggerFactory]

然后又换了一下，把logback-classic放在上面，结果如下：

log4j:WARN No appenders could be found for logger (org.jboss.logging).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
2018-08-13 20:48:32.894:INFO:/:Initializing Spring root WebApplicationContext
SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/D:/m2space/repository/ch/qos/logback/logback-classic/1.2.0/logback-classic-1.2.0.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/D:/m2space/repository/org/slf4j/slf4j-log4j12/1.7.21/slf4j-log4j12-1.7.21.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 [ch.qos.logback.classic.util.ContextSelectorStaticBinder]

再看logback-classic 默认level是debug，怪不得用这包不配logback.xml全打debug呢

  public LoggerContext()
  {
    this.loggerCache = new ConcurrentHashMap();
    
    this.loggerContextRemoteView = new LoggerContextVO(this);
    this.root = new Logger("ROOT", null, this);
    this.root.setLevel(Level.DEBUG);
    this.loggerCache.put("ROOT", this.root);
    initEvaluatorMap();
    this.size = 1;
    this.frameworkPackages = new ArrayList();
  }

那为什么那个是info呢，因为slf4j-log4j12的
StaticLoggerBinder无参构造方法中初始化loggerFactory为new Log4jLoggerFactory()，Log4jLoggerFactory的LogManager是org.apache.log4j.LogManager，默认是找log4j.xml

尝试把两个依赖都去掉，会打印如下：

SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.

也就是slf4j-api的LoggerFactory的bind方法

private static final void bind()
  {
    try
    {
      Set<URL> staticLoggerBinderPathSet = null;
      if (!isAndroid())
      {
        staticLoggerBinderPathSet = findPossibleStaticLoggerBinderPathSet();
        reportMultipleBindingAmbiguity(staticLoggerBinderPathSet);
      }
      StaticLoggerBinder.getSingleton();
      INITIALIZATION_STATE = 3;
      reportActualBinding(staticLoggerBinderPathSet);
      fixSubstituteLoggers();
      replayEvents();
      
      SUBST_FACTORY.clear();
    }
    catch (NoClassDefFoundError ncde)
    {
      String msg = ncde.getMessage();
      if (messageContainsOrgSlf4jImplStaticLoggerBinder(msg))
      {
        INITIALIZATION_STATE = 4;
        Util.report("Failed to load class \"org.slf4j.impl.StaticLoggerBinder\".");
        Util.report("Defaulting to no-operation (NOP) logger implementation");
        Util.report("See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.");
      }
      else
      {
        failedBinding(ncde);
        throw ncde;
      }
    }
    catch (NoSuchMethodError nsme)
    {
      String msg = nsme.getMessage();
      if ((msg != null) && (msg.contains("org.slf4j.impl.StaticLoggerBinder.getSingleton()")))
      {
        INITIALIZATION_STATE = 2;
        Util.report("slf4j-api 1.6.x (or later) is incompatible with this binding.");
        Util.report("Your binding is version 1.5.5 or earlier.");
        Util.report("Upgrade your binding to version 1.6.x.");
      }
      throw nsme;
    }
    catch (Exception e)
    {
      failedBinding(e);
      throw new IllegalStateException("Unexpected initialization failure", e);
    }
  }

那，这时候调用接口，返回成功了，中间明明有logger.info打印语句，可是控制台就没有显示出来，以后要用什么可以心里有点逼数了。