VB.NET中Web请求如何通过Newtonsoft.Json提取accessToken

先修正原代码中的请求错误 #

原代码里request.ContentLength = 0是错误的，服务器需要知道请求体的长度才能正确接收数据，应该改成：

request.ContentLength = bArray.Length

另外，建议用Using语句管理流对象，避免资源泄漏，原代码直接Close流的写法不够安全。

提取accessToken的两种实现方式 #

方式一：使用动态类型（无需定义实体类）

直接将响应JSON反序列化为动态对象，通过属性名直接获取accessToken：

Dim accessToken As String
Dim body As String = "{""username"": ""abc"", ""password"": ""abc123""}"
Dim request As WebRequest = WebRequest.Create("http://xxx.xxx.xxx.xxx/api/getaccessToken")
request.Method = "POST"
request.ContentType = "application/json"

Dim bArray As Byte() = Encoding.UTF8.GetBytes(body)
request.ContentLength = bArray.Length

' Using语句自动释放流资源
Using dStream As Stream = request.GetRequestStream()
    dStream.Write(bArray, 0, bArray.Length)
End Using

' 处理响应
Using response As WebResponse = request.GetResponse()
    Using streamReader As New StreamReader(response.GetResponseStream())
        Dim streamR = streamReader.ReadToEnd()
        ' 反序列化为动态对象
        Dim jsonResponse = JsonConvert.DeserializeObject(Of Object)(streamR)
        ' 提取accessToken
        accessToken = jsonResponse("accessToken").ToString()
    End Using
End Using

Return accessToken

方式二：使用强类型实体类（更安全）

先定义和响应结构匹配的类，再反序列化，这种方式在编译期就能检查属性名是否正确，避免运行时错误：

' 定义响应实体类
Public Class TokenResponse
    Public Property accessToken As String
    Public Property expires As String
End Class

' 主代码部分
Dim accessToken As String
Dim body As String = "{""username"": ""abc"", ""password"": ""abc123""}"
Dim request As WebRequest = WebRequest.Create("http://xxx.xxx.xxx.xxx/api/getaccessToken")
request.Method = "POST"
request.ContentType = "application/json"

Dim bArray As Byte() = Encoding.UTF8.GetBytes(body)
request.ContentLength = bArray.Length

Using dStream As Stream = request.GetRequestStream()
    dStream.Write(bArray, 0, bArray.Length)
End Using

Using response As WebResponse = request.GetResponse()
    Using streamReader As New StreamReader(response.GetResponseStream())
        Dim streamR = streamReader.ReadToEnd()
        ' 反序列化为强类型对象
        Dim tokenResponse = JsonConvert.DeserializeObject(Of TokenResponse)(streamR)
        ' 直接获取属性值
        accessToken = tokenResponse.accessToken
    End Using
End Using

Return accessToken

内容的提问来源于stack exchange，提问作者user19613128