通过反射机制，找到相应的Left或者Right广告

type SearchAdsObj struct {Left     PositionAdsObj `json:"left"`Right    PositionAdsObj `json:"right"`
}func getFieldByName(obj SearchAdsObj, fieldName string) (interface{}, error) {fmt.Printf("getFieldByName: %s \n", fieldName)val := reflect.ValueOf(obj)// fmt.Printf("getFieldByName val %v \n", val)if val.Kind() != reflect.Struct {fmt.Printf("getFieldByName input is not a struct")return nil, fmt.Errorf("getFieldByName input is not a struct")}field := val.FieldByName(fieldName)if !field.IsValid() {fmt.Printf("getFieldByName field %s not found in the struct", fieldName)return nil, fmt.Errorf("getFieldByName field %s not found in the struct", fieldName)}var inter interface{} = fieldif myStruct, ok := inter.(PositionAdsObj); ok {// 如果转换成功，myStruct现在包含MyStruct类型的值return myStruct, nil} else {// 如果转换失败，说明myInterface不包含MyStruct类型的值fmt.Println("Conversion failed, myInterface does not contain a PositionAdsObj")return nil, fmt.Errorf("Conversion failed, myInterface does not contain a PositionAdsObj")}
}

注意 getFieldByName 传入的是SearchAdsObj具体类型的实体，而不能是：obj interface{}

func getFieldByName(obj interface{}, fieldName string) (interface{}, error) {

因为反射访问结构体内部字段时候，需要操作的对象是一个实际类型的结构体