Example.java

DelegatingRequest<JSONObject> tokenRequest = new DelegatingRequest<JSONObject>(
		Method.POST, TOKEN_URL, NewtorkResponseParser.jsonObjectParser,
		new Listener<JSONObject>() {

			@Override
			public void onResponse(JSONObject response) {
				ACCESS_TOKEN = response.optString("access_token");
				// Do the rest of the treatment
			}
		}, new ErrorListener() {
			@Override
			public void onErrorResponse(VolleyError error) {
				Log.e(TAG, "Error during request");
				error.printStackTrace();
			}
		});
String auth = "Basic "
		+ Base64.encodeToString(("<CONSUMER_KEY>" + ":"
				+ "<CONSUMER_SECRET>").getBytes(), Base64.NO_WRAP);
tokenRequest.addHeader("Authorization", auth);
tokenRequest.addParam("grant_type", "client_credentials");
queue.add(tokenRequest);