code: public static Field getSoftDeleteColumn(Class<?> clazz) {
  		List<Field> fields = getColumns(clazz);
  		
  		for(Field field : fields) {
  			Column column = field.getAnnotation(Column.class);
  			if(column.softDelete() != null && column.softDelete().length == 2
  					&& !column.softDelete()[0].trim().isEmpty()
  					&& !column.softDelete()[1].trim().isEmpty()) {
  				return field;
  			}
  		}
  		return null;
  	}
docs: 获得软删除标记字段，最多只能返回1个。
  @param clazz
  @return 如果没有则返回null