docs: private static synchronized void setImplementation(Class<? extends Log> implClass) {
      try {
        //如果已经实现，则直接跳过
        if(logConstructor != null) {
          return;
        }
  
        Constructor<? extends Log> candidate = implClass.getConstructor(String.class);
        Log log = candidate.newInstance(LogFactory.class.getName());
        log.debug("Logging initialized using '" + implClass + "' adapter.");
        logConstructor = candidate;
      } catch (Throwable t) {
        // do nothing
      }
    }