I am trying to get a JSON response from our server and the response string seems is always being truncated when the string length reaches to around 5525 characters.
String line = reader.readLine();
I believe the above line in your program is the problem. It reads a line from the server response and the String line. If the server response has a line feed (\n) then the reader will not be able to read the line after that.
use the following to avoid that..
if (responseCode == HttpURLConnection.HTTP_OK) {
InputStream in = ((URLConnection) httpConnection).getInputStream();
int len = 0;
byte[] data1 = new byte[1024];
while ( -1 != (len = in.read(data1)) )
dataFromServer.append(new String(data1, 0, len));
}