How to read JSON http post response using VB

Question

I have the following code, it connects to PHP server and retrieve data successfully, i'm not very good with VB, how can i read the JSON response text and extract it's elements?

Public Class Form1
    Private Sub submit_Click(sender As System.Object, e As System.EventArgs) Handles submit.Click
        Dim user As String
        Dim pass As String
        user = uname.Text
        pass = passwd.Text

        Dim request As WebRequest = WebRequest.Create("http://domain.com/test.php")
        request.Method = "POST"
        Dim postData As String
        postData = "username=" & user & "&password=" & pass
        Dim byteArray As Byte() = Encoding.UTF8.GetBytes(postData)
        request.ContentType = "application/x-www-form-urlencoded"
        request.ContentLength = byteArray.Length
        Dim dataStream As Stream = request.GetRequestStream()
        dataStream.Write(byteArray, 0, byteArray.Length)
        dataStream.Close()
        Dim response As WebResponse = request.GetResponse()
        Console.WriteLine(CType(response, HttpWebResponse).StatusDescription)
        dataStream = response.GetResponseStream()
        Dim reader As New StreamReader(dataStream)
        Dim responseFromServer As String = reader.ReadToEnd()
        If responseFromServer = "0" Then
            MsgBox("Login Failed")
        Else
            MsgBox("json data")
        End If
        reader.Close()
        dataStream.Close()
        response.Close()
    End Sub
End Class

The JSON response would be something like:

{"comments": [
               {
               "comment" : "some text",
               "date"    : "some date",
               "user"    : "user name"
               },
               {
               "comment" : "some text",
               "date"    : "some date",
               "user"    : "user name"
               }
             ],
 "messages": [ .... ]
}

How to output the json string into:

Comments
user      date      comment
-----------------------------------
user 1    date 1    comment 1
user 2    date 2    comment 2

Messages
user      date      message
-----------------------------------
user 1    date 1    message 1
user 2    date 2    message 2

Answer 1

After long research and many tests I found out a very nice extension called Newtonsoft.json, it's extremely simple and can be installed from package manager console like this:

install-package Newtonsoft.json

And include it like this:

Imports Newtonsoft.Json
Imports Newtonsoft.Json.Linq

Then all i needed to do is to declare the elements names and values like this:

Else
    Dim json As String = responseFromServer
    Dim ser As JObject = JObject.Parse(json)
    Dim data As List(Of JToken) = ser.Children().ToList
    Dim output As String = ""

    For Each item As JProperty In data
        item.CreateReader()
        Select Case item.Name
            Case "comments"
                output += "Comments:" + vbCrLf
                For Each comment As JObject In item.Values
                    Dim u As String = comment("user")
                    Dim d As String = comment("date")
                    Dim c As String = comment("comment")
                    output += u + vbTab + d + vbTab + c + vbCrLf
                Next

            Case "messages"
                output += "Messages:" + vbCrLf
                For Each msg As JObject In item.Values
                    Dim f As String = msg("from")
                    Dim t As String = msg("to")
                    Dim d As String = msg("date")
                    Dim m As String = msg("message")
                    Dim s As String = msg("status")
                    output += f + vbTab + t + vbTab + d + vbTab + m + vbTab + s + vbCrLf
                Next

        End Select
    Next
    MsgBox(output)
End If

hope someone will find this useful

Answer 2

@razzak is absolutely right to use the Json.Net NuGet package. Another option that would cut this down dramatically, is to use the built in DeserializeObject function. As long as you have a well define model, then you can deserialize the Json right into an instance of the object using something like this:

dim myObject as MyDefinedObject = JsonConvert.DeserializeObject(responseFromServer)

or this in C#

MyDefinedObject m = JsonConvert.DeserializeObject<MyDefinedObject>(responseFromServer);

Also, if you don't want to loop, you could also select tokens using something like this:

Dim d = ser.SelectToken("$..resources[?(@)].travelDistance")

This code above was used to locate the travelDistance between two points from the Bing API. If you have ever dealt with the Bing or Google Map REST APIs, then you know the JSon is generally too large to loop through the data when you are looking for very specific values.

The JSon.Net website has a blog page that goes through some additional examples:

http://james.newtonking.com/json