code: public Log getLog(Class<?> clazz) {
  		Log log = logCache.get(clazz);
  		if (null == log) {
  			log = createLog(clazz);
  			logCache.put(clazz, log);
  		}
  		return log;
  	}
docs: 获得日志对象
  
  @param clazz 日志对应类
  @return 日志对象