Método para obtener JSON desde una URL en Android.

.java

public String getJsonFromUrl(String urlString) {
    StringBuilder result = new StringBuilder();
    HttpURLConnection urlConnection = null;
    try {
        URL url = new URL(urlString);
        urlConnection = (HttpURLConnection) url.openConnection();
        InputStream in = new BufferedInputStream(urlConnection.getInputStream());
        BufferedReader reader = new BufferedReader(new InputStreamReader(in));
        String line;
        while ((line = reader.readLine()) != null) {
            result.append(line);
        }

    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        assert urlConnection != null;
        urlConnection.disconnect();
    }
    return result.toString();
}