private static String mappingKey(Map<String, String> mapping, String fieldName) {
		if (MapUtil.isEmpty(mapping)) {
			return fieldName;
		}
		return ObjectUtil.defaultIfNull(mapping.get(fieldName), fieldName);
	}
private static String mappingKey ( Map < String , String > mapping , String fieldName ) { if ( MapUtil . isEmpty ( mapping ) ) { return fieldName ; } return ObjectUtil . defaultIfNull ( mapping . get ( fieldName ) , fieldName ) ; }
获取指定字段名对应的映射值

@param mapping 反向映射Map
@param fieldName 字段名
@return 映射值，无对应值返回字段名
@since 4.1.10