How to convert a Java String to an ASCII byte array?
I found the solution. Actually Base64 class is not available in Android. Link is given below for more information.
byte[] byteArray;
byteArray= json.getBytes(StandardCharsets.US_ASCII);
String encoded=Base64.encodeBytes(byteArray);
userLogin(encoded);
Here is the link for Base64 class: http://androidcodemonkey.blogspot.com/2010/03/how-to-base64-encode-decode-android.html