VB.Net使用Newtonsoft解析JSON遇StartArray错误求助

问题背景 #

我用VB开发，使用Newtonsoft解析一段已通过JSONLINT验证的合法JSON时失败，报错信息如下：

Error reading JObject from JsonReader. Current JsonReader item is not an object: StartArray. Path '', line 1, position 1.

目标JSON内容：

[{
    "payload": {
        "MainBlock": {
            "S0": {
                "interfaceId": "IF-XXX",
                "schemaVersion": "1.1.1",
                "eventCode": "[ABCPeriodData]"
            },
            "S1": {
                "environment": "DEV",
                "senderUniqueReference": "S-005-1234567abc-SUP-20222313-12345687A",
                "sentTimestamp": "2022-12-31T12:35:45\u002B06:30",
                "senderId": "4ce0a6cd4b",
                "senderRole": "ABC",
                "DIPConnectionProviderId": "1009012345"
            },
            "A0": {
                "always": ["SUP", "SDS", "ADS", "UMDS"]
            },
            "D0": {
                "transactionId": "T-022-4ce0a6cd4b-ABC-20230503-000404",
                "transactionTimestamp": "2023-05-03T13:34:34\u002B00:00",
                "publicationId": "PUB-XXX"
            }
        },
        "SecondBlock": {
            "B903List": [{
                "calculationDay": {
                    "calculationDayDate": "2022-12-31T12:35:45\u002B06:30",
                    "calculationPeriodDuration": 30
                },
                "XYZcalculationPeriods": [{
                    "XYZroup": {
                        "GSPGroupID": "_K",
                        "connectionTypeIndicator": "W",
                        "domesticPremiseIndicator": true,
                        "marketSegmentIndicator": "A",
                        "measurementQuantityID": "AI"
                    },
                    "XYZroupcalculationPeriods": [{
                        "calculationPeriodEffectiveToDateTime": "2022-12-31T12:35:45\u002B06:30",
                        "loadShapePeriodValue": "123456789.123",
                        "defaultLoadShapeFlag": "A"
                    }, {
                        "calculationPeriodEffectiveToDateTime": "2022-12-31T12:35:45\u002B06:30",
                        "loadShapePeriodValue": "123456789.123",
                        "defaultLoadShapeFlag": "A"
                    }]
                }]
            }]
        }
    }
}]

我之前用JObject.Parse()解析其他JSON文件正常，但这段JSON以数组开头，用同样方法就报错，尝试以下代码仍未解决：

Dim o As JObject = JObject.Parse(Json)
Dim results As List(Of JToken) = o.Children().ToList
For Each item As JProperty In results
    item.CreateReader()
    If item.Value.Type = JTokenType.Array Then
        Dim results2 As List(Of JToken) = item.Value.ToList
        For Each subitem As JObject In results2
            WorkingDictionary = New Dictionary(Of String, String)
            Dim results3 As List(Of JToken) = subitem.Children().ToList
            For Each temp2 As JProperty In results3
                temp2.CreateReader()
                Try
                    Debug.Print(temp2.Name)
                    WorkingDictionary.Add(temp2.Name, temp2.Value.ToString)
                Catch ex As Exception
                    Debug.Print(ex.StackTrace)
                    Debug.Print(ex.Message)
                End Try
            Next
            RetVal.Add(WorkingDictionary)
        Next
    Else
        Debug.Print(item.Name.ToString + "   " + item.Value.ToString)
    End If
Next

解决方案 #

核心问题原因 #

你的JSON最外层是数组（以[开头），但你使用了仅能解析单个JSON对象（以{开头）的JObject.Parse()方法，因此触发"StartArray"类型不匹配错误。

修正后的解析代码 #

改用JArray.Parse()解析外层数组，再逐层遍历嵌套结构：

Try
    ' 解析最外层数组
    Dim arr As JArray = JArray.Parse(Json)
    ' 遍历数组中的每个对象（此示例数组仅含一个元素）
    For Each obj As JObject In arr
        ' 获取payload对象
        Dim payload As JObject = obj("payload")
        
        ' 处理MainBlock下的数据
        Dim mainBlock As JObject = payload("MainBlock")
        Debug.Print("interfaceId: " & mainBlock("S0")("interfaceId").ToString())
        Debug.Print("senderUniqueReference: " & mainBlock("S1")("senderUniqueReference").ToString())
        
        ' 处理SecondBlock下的数据
        Dim secondBlock As JObject = payload("SecondBlock")
        Dim b903List As JArray = secondBlock("B903List")
        For Each b903Item As JObject In b903List
            Dim calculationDay As JObject = b903Item("calculationDay")
            Debug.Print("calculationPeriodDuration: " & calculationDay("calculationPeriodDuration").ToString())
            
            Dim xyzPeriods As JArray = b903Item("XYZcalculationPeriods")
            For Each xyzItem As JObject In xyzPeriods
                Dim xyzGroup As JObject = xyzItem("XYZroup")
                Debug.Print("GSPGroupID: " & xyzGroup("GSPGroupID").ToString())
                
                Dim xyzCalcPeriods As JArray = xyzItem("XYZroupcalculationPeriods")
                For Each periodItem As JObject In xyzCalcPeriods
                    Debug.Print("loadShapePeriodValue: " & periodItem("loadShapePeriodValue").ToString())
                Next
            Next
        Next
    Next
Catch ex As Exception
    Debug.Print(ex.StackTrace)
    Debug.Print(ex.Message)
End Try

字典收集版代码（适配你的原有需求） #

如果仍需要将数据收集到字典中，调整后的代码如下：

Try
    Dim arr As JArray = JArray.Parse(Json)
    For Each obj As JObject In arr
        Dim payload As JObject = obj("payload")
        ' 遍历payload下的所有顶级块
        For Each prop As JProperty In payload.Properties()
            WorkingDictionary = New Dictionary(Of String, String)
            WorkingDictionary.Add(prop.Name, prop.Value.ToString())
            RetVal.Add(WorkingDictionary)
        Next
    Next
Catch ex As Exception
    Debug.Print(ex.StackTrace)
    Debug.Print(ex.Message)
End Try

关键要点总结 #

• 区分JSON最外层结构：对象用JObject.Parse()，数组用JArray.Parse()
• 解析嵌套结构时，通过JToken("键名")逐层获取值，注意判断目标节点是对象还是数组
• 遍历对象的所有属性时，使用Properties()方法获取键值对集合

内容的提问来源于stack exchange，提问作者Tym