code: public static String getPackage(Class<?> clazz) {
  		if (clazz == null) {
  			return StrUtil.EMPTY;
  		}
  		final String className = clazz.getName();
  		int packageEndIndex = className.lastIndexOf(StrUtil.DOT);
  		if (packageEndIndex == -1) {
  			return StrUtil.EMPTY;
  		}
  		return className.substring(0, packageEndIndex);
  	}
docs: 获得给定类所在包的名称<br>
  例如：<br>
  com.xiaoleilu.hutool.util.ClassUtil =》 com.xiaoleilu.hutool.util
  
  @param clazz 类
  @return 包名