How to read a JSON response using HttpClient in vb.net

Question

I have built a java routine for accessing a WEB API service, however I am struggling with the VB equivalent for ASP.Net. I get the API response, but I don't know how to convert it to the json elements.

The java version is:

    public boolean canLogin(){
    HttpClient httpclient = new DefaultHttpClient();
    HttpPost httppost = new HttpPost(hostURL + TOKEN_ACCESS_URL);
    httppost.addHeader("Accept", "application/json");

    // Add the post content
    List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(3);
    nameValuePairs.add(new BasicNameValuePair("grant_type", "password"));
    nameValuePairs.add(new BasicNameValuePair("username", accessUserName));
    nameValuePairs.add(new BasicNameValuePair("password", accessPassword));
    try {
        httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
    } catch (UnsupportedEncodingException e1) {
        mobileLogDataHandler.ToLog(LogType.Error, "UnsupportedEncodingException closing data stream with error: " + e1.getLocalizedMessage() + ",detail:" + e1.getMessage() + " in canLogin", mResolver, RemoteDataHandler.class);
        return false;
    }

    // post the server
    InputStream inputStream = null;
    String result = null;
    try {
        HttpResponse response = httpclient.execute(httppost);
        if (response.getStatusLine().getStatusCode()!=200){
            mobileLogDataHandler.ToLog(LogType.Error, "Failed to get server token with error: " + response.getStatusLine().toString() + " in canLogin", mResolver, this.getClass());
            return false;
        }
        HttpEntity entity = response.getEntity();
        inputStream = entity.getContent();
        BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream, "UTF-8"), 8);// json is UTF-8 by default
        StringBuilder sb = new StringBuilder();
        String line = null;
        while ((line = reader.readLine()) != null)
        {
            sb.append(line + "\n");
        }
        result = sb.toString();
        inputStream.close();

    } catch (ClientProtocolException e) {
        mobileLogDataHandler.ToLog(LogType.Error, "ClientProtocolException trying to get bearer token from server with error: " + e.getLocalizedMessage() + ",detail:" + e.getMessage() + " in canLogin", mResolver, this.getClass());
        return false;
    } catch (IOException e) {
        mobileLogDataHandler.ToLog(LogType.Error, "IOException trying to get bearer token from server with error: " + e.getLocalizedMessage() + ",detail:" + e.getMessage() + " in canLogin", mResolver, this.getClass());
        return false;
    }

    //read the response content
    try{
        JSONObject jObject = new JSONObject(result);
        bearerToken =  jObject.getString("access_token");
        String expiryIntervalInSeconds = jObject.getString("expires_in");
        return canSaveNewBearerToken(bearerToken, expiryIntervalInSeconds);
    } catch (JSONException e){
        mobileLogDataHandler.ToLog(LogType.Error, "JSON error reading data sent from server for bearer token request with error: " + e.getLocalizedMessage() + ",detail:" + e.getMessage() + " in canLogin", mResolver, this.getClass());
        return false;
    }

But in my VB version - this is all I have. How can I read it so that I get the json objects out of it:

Public Function canLogin() As Boolean
    Dim client As HttpClient = New HttpClient
    client.DefaultRequestHeaders.Accept.Add(
            New System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("application/json"))

    'Dim content As HttpContent = New StringContent("grant_type=password&username=" & mAccessUserName & "&password=" & mAccessPassword)
    Dim urlEncodedList As New List(Of KeyValuePair(Of String, String))
    urlEncodedList.Add(New KeyValuePair(Of String, String)("grant_type", "password"))
    urlEncodedList.Add(New KeyValuePair(Of String, String)("username", mAccessUserName))
    urlEncodedList.Add(New KeyValuePair(Of String, String)("password", mAccessPassword))
    Dim content As New FormUrlEncodedContent(urlEncodedList)
    'content.Headers.ContentType = New Headers.MediaTypeHeaderValue("application/x-www-form-urlencoded")  'not sure if i need this

    Dim response As HttpResponseMessage = client.PostAsync(New Uri(mHostURL & TOKEN_ACCESS_URL), content).Result

    If response.IsSuccessStatusCode Then
        Return True
    Else
        Return False
    End If


End Function

Any help appreciated.

Badrinarayanan Lakshmiraghavan · Accepted Answer · 2014-04-01 08:15:27Z

7

Dim response As HttpResponseMessage = client.PostAsync(
                               New Uri("someuri"), content).Result

If response.IsSuccessStatusCode Then
    Dim json As String = response.Content.ReadAsStringAsync().Result
    Dim bearerToken As String = DirectCast(
               JObject.Parse(json).SelectToken("access_token"),
                                    String)
    Return True
Else
    Return False
End If

PS. Make sure you have a reference to JSON.NET. Also, using .Result in ASP.NET is very problematic and can result easily in deadlocks. Better use await.

edited Apr 1, 2014 at 8:15

answered Apr 1, 2014 at 8:09

Badrinarayanan Lakshmiraghavan

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1 Comment

K K Over a year ago

Works in year 2024 too, thanks

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