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How to post json object to servlet?

TingZengTingZeng USMember ✭✭

My Xamarin side of code :

public class SendData{

public int TransactionId { set; get; }
public float DollarAmount { set; get; }


public async Task SendAjax(){

    HttpClient oHttpClient = new HttpClient();

    SendData data = new SendData();
    data.TransactionId = 4;
    data.DollarAmount = (float) 1111.11;

    var temp = "{\"TransactionId\", 4}";
    var sData = JsonConvert.SerializeObject(data);

    var oTaskPostAsync = oHttpClient.PostAsync(serverURL, new StringContent(oJsonObject.ToString(), Encoding.UTF8, sContentType))

Servlet side:

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    Object myObj = request.getParameter("jsondata");


I got null for myObj. I tried directly add TransactionId to the oJsonObject, and read TransactionId on servlet, still null data.

Any idea ? It is driving me nuts. Thx.


  • XavierPerseguersXavierPerseguers CHMember ✭✭✭

    I'm doing it like that and it works in my app:

    var payload = JsonConvert.SerializeObject(data);
    StringContent contents = new StringContent(payload, System.Text.Encoding.UTF8);
    contents.Headers.ContentType = "application/json";
    string responseBody = null;
    HttpResponseMessage response = null;
    try {
        response = await Client.PostAsync(requestUri, contents);
        response.Content.Headers.ContentType = new MediaTypeHeaderValue("application/json");
        responseBody = await response.Content.ReadAsStringAsync();
    } catch (HttpRequestException hre) {
  • TingZengTingZeng USMember ✭✭

    Thanks for replying. I found a solution myself. I have not tried yours, I will give it a shot later.

    public async Task SendAjax(IEnumerable<KeyValuePair<string, string>> dataPairs){

       HttpClient oHttpClient = new HttpClient();
        var content = new FormUrlEncodedContent(dataPairs);
            var oTaskPostAsync = oHttpClient.PostAsync(serverURL, content);
            var response = await oTaskPostAsync;
            var result = await response.Content.ReadAsStringAsync();
            return result;


    The key is to embed the data in a form format and send. This is because the receiver end is a servlet doPost(HttpServletRequest request, HttpServletResponse response).

    So far, I found the servlet only works well with either query data (embedded in query or form data). If Json data, I can only get it to work with Json sent by Javascript.

  • TingZengTingZeng USMember ✭✭

    Just tried your solution, it is the same error I got before. The Json data would not be interpreted correctly. All are null values on Servlet side. Form data works. Hope this would help someone who has the same issue.

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