To send JSON object in server you have to do the following steps:-
1) Create JSON object
2) Set the header of HttpPost to "Content-Type", "application/json"
3) Now call postJsonObjectToServer method(define below) :-

public static String postJsonObjectToServer(JSONObject jsonObject, String url)
    {       
        final DefaultHttpClient client = new DefaultHttpClient();
        HttpPost method=null;
        try {
            method = new HttpPost(new URI(url));
            method.setHeader( "Content-Type", "application/json" );

            method.setEntity(new ByteArrayEntity(jsonObject.toString().getBytes("UTF8")));
        } catch (UnsupportedEncodingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }       
        catch (URISyntaxException e) 
        {
            e.printStackTrace();
        }
        HttpResponse res=null;
        try 
        {
            if(client!=null)
                res = client.execute(method);
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        if(res!=null)
        {
            HttpEntity entity=res.getEntity();
            InputStream input=null;
            try {
                input = res.getEntity().getContent();
                byte[] data = new byte[256];
                int len = 0;
                int size = 0;
                StringBuffer raw = new StringBuffer();

                while ( -1 != (len = input.read(data)) )
                {
                    raw.append(new String(data, 0, len));
                    size += len;
                }
                input.close();
                return raw.toString();
            } catch (IllegalStateException e) {
                e.printStackTrace();
                return "";
            } catch (IOException e) {

                e.printStackTrace();
                return "";
            }
        }
        else
        {
            return "";
        }
    }

Call the above method in background thread.
Similarly you can send the JSONArray to the server.