Android how to send data string via Json to server?

you can do it by using query string. But for that you need a api for server-side. To send data on server side u can use this code:-

public String connect(String url) 
    {//for connect to database(QueryString API)
        String userID = null;
        HttpClient httpc = new DefaultHttpClient();
        try 
        {
        HttpPost post = new HttpPost(url);

            HttpResponse response = httpc.execute(post);
            if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) 
            {
                userID = EntityUtils.toString(response.getEntity());
                Log.v("Login response", "" + userID);
            }
        }   
        catch (ClientProtocolException e) 
        {
            e.printStackTrace();
        } 
        catch (IOException e) 
        {
            e.printStackTrace();
        }
        return userID;
    }

public void abcd(String a1, String a2, String a3,
            String a4, String a5) {

        String QS ="";//acc. to ur data
        String finalURL2 = url + QS;

        String result2 = connect(finalURL2);
        Log.v("message", result2);
    }

it Depends how your server side is implemented Normally sending data Requires Either HTTPPost Method or HTTPPut methods. More commonly used is HTTPPost methods That has header data and Body Data

you need to do it in following way

1- convert your json object to String

user.toString();
2- add Targeted URL

String URL="Enter URL here";
3- add url to the request

response = dohttpPostWithCode(URL.toString(),user.toString());
response is String [ ] that have 2 index i- for response code ii- for data

4- method to handle data

 public String[] dohttpPostWithCode(String url,String postParameters ) throws Exception {
         URL weburl = new URL(url);
         URI uri = new URI(weburl.getProtocol(), weburl.getUserInfo(), weburl.getHost(), weburl.getPort(), weburl.getPath(), weburl.getQuery(), weburl.getRef());
            BufferedReader in = null;
            String[] result = new String[2];         
            try {
                 HttpParams httpParameters = new BasicHttpParams();
                // Set the timeout in milliseconds until a connection is established.
                int timeoutConnection = 20000;
                HttpConnectionParams.setConnectionTimeout(httpParameters, timeoutConnection);
                // Set the default socket timeout (SO_TIMEOUT) 
                // in milliseconds which is the timeout for waiting for data.
                int timeoutSocket = 20000;
                HttpConnectionParams.setSoTimeout(httpParameters, timeoutSocket);
                HttpURLConnection httpURL=(HttpURLConnection) weburl.openConnection();
                httpURL.setDoOutput(true);
                httpURL.setDoInput(true);
                httpURL.setRequestMethod("POST");
                HttpClient client =new  DefaultHttpClient(httpParameters);            
                HttpPost httpPost = new HttpPost(uri);
                //httpPost.addHeader("language","en");
                httpPost.addHeader("Content-Type",  "application/json");

               // StringEntity entity = new StringEntity(postParameters, HTTP.UTF_8);
                httpPost.setEntity(new StringEntity(postParameters));
               // httpPost.setEntity(entity);
               // httpPost.setEntity(new UrlEncodedFormEntity(postParameters));
                HttpResponse response = client.execute(httpPost);               
                in = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));
                StringBuffer sb = new StringBuffer("");
                String line = "";
                String NL = System.getProperty("line.separator");

                while ((line = in.readLine()) != null) {
                    sb.append(line + NL);
                }
                in.close();
/*              String result = sb.toString();
                return result;*/
                result[0] = response.getStatusLine().getStatusCode()+"";
                result[1] = sb.toString();
                return result;
            } finally {
                if (in != null) {
                    try {
                        in.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }
        }