Java tutorial
/* * Copyright (C) 2013 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.example.marcieltorres.nfcproject_serverapp.cardreader; import android.nfc.NfcAdapter; import android.nfc.Tag; import android.nfc.tech.IsoDep; import com.example.marcieltorres.nfcproject_serverapp.MainActivity; import com.example.marcieltorres.nfcproject_serverapp.controllers.WebserviceController; import org.json.JSONException; import java.io.IOException; import java.lang.ref.WeakReference; import java.util.Arrays; /** * Callback class, invoked when an NFC card is scanned while the device is running in reader mode. * * Reader mode can be invoked by calling NfcAdapter */ public class LoyaltyCardReader implements NfcAdapter.ReaderCallback { private static final String TAG = "LoyaltyCardReader"; // AID for our loyalty card service. private static final String SAMPLE_LOYALTY_CARD_AID = "F222222222"; // ISO-DEP command HEADER for selecting an AID. // Format: [Class | Instruction | Parameter 1 | Parameter 2] private static final String SELECT_APDU_HEADER = "00A40400"; // "OK" status word sent in response to SELECT AID command (0x9000) private static final byte[] SELECT_OK_SW = { (byte) 0x90, (byte) 0x00 }; // Weak reference to prevent retain loop. mAccountCallback is responsible for exiting // foreground mode before it becomes invalid (e.g. during onPause() or onStop()). private WeakReference<AccountCallback> mAccountCallback; public interface AccountCallback { public void onAccountReceived(String account); } public LoyaltyCardReader(AccountCallback accountCallback) { mAccountCallback = new WeakReference<AccountCallback>(accountCallback); } /** * Callback when a new tag is discovered by the system. * * <p>Communication with the card should take place here. * * @param tag Discovered tag */ @Override public void onTagDiscovered(Tag tag) { //Log.i(TAG, "New tag discovered"); // Android's Host-based Card Emulation (HCE) feature implements the ISO-DEP (ISO 14443-4) // protocol. // // In order to communicate with a device using HCE, the discovered tag should be processed // using the IsoDep class. IsoDep isoDep = IsoDep.get(tag); if (isoDep != null) { try { // Connect to the remote NFC device isoDep.connect(); // Build SELECT AID command for our loyalty card service. // This command tells the remote device which service we wish to communicate with. //Log.i(TAG, "Requesting remote AID: " + SAMPLE_LOYALTY_CARD_AID); byte[] command = BuildSelectApdu(SAMPLE_LOYALTY_CARD_AID); // Send command to remote device //Log.i(TAG, "Sending: " + ByteArrayToHexString(command)); byte[] result = isoDep.transceive(command); // If AID is successfully selected, 0x9000 is returned as the status word (last 2 // bytes of the result) by convention. Everything before the status word is // optional payload, which is used here to hold the account number. int resultLength = result.length; byte[] statusWord = { result[resultLength - 2], result[resultLength - 1] }; byte[] payload = Arrays.copyOf(result, resultLength - 2); if (Arrays.equals(SELECT_OK_SW, statusWord)) { // The remote NFC device will immediately respond with its stored account number String accountNumber = new String(payload, "UTF-8"); //Log.i(TAG, "Received: " + accountNumber); // Inform CardReaderFragment of received account number mAccountCallback.get().onAccountReceived(accountNumber); mAccountCallback.get().onAccountReceived(accountNumber); } } catch (IOException e) { //Log.e(TAG, "Error communicating with card: " + e.toString()); } } } /** * Build APDU for SELECT AID command. This command indicates which service a reader is * interested in communicating with. See ISO 7816-4. * * @param aid Application ID (AID) to select * @return APDU for SELECT AID command */ public static byte[] BuildSelectApdu(String aid) { // Format: [CLASS | INSTRUCTION | PARAMETER 1 | PARAMETER 2 | LENGTH | DATA] return HexStringToByteArray(SELECT_APDU_HEADER + String.format("%02X", aid.length() / 2) + aid); } /** * Utility class to convert a byte array to a hexadecimal string. * * @param bytes Bytes to convert * @return String, containing hexadecimal representation. */ public static String ByteArrayToHexString(byte[] bytes) { final char[] hexArray = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' }; char[] hexChars = new char[bytes.length * 2]; int v; for (int j = 0; j < bytes.length; j++) { v = bytes[j] & 0xFF; hexChars[j * 2] = hexArray[v >>> 4]; hexChars[j * 2 + 1] = hexArray[v & 0x0F]; } return new String(hexChars); } /** * Utility class to convert a hexadecimal string to a byte string. * * <p>Behavior with input strings containing non-hexadecimal characters is undefined. * * @param s String containing hexadecimal characters to convert * @return Byte array generated from input */ public static byte[] HexStringToByteArray(String s) { int len = s.length(); byte[] data = new byte[len / 2]; for (int i = 0; i < len; i += 2) { data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4) + Character.digit(s.charAt(i + 1), 16)); } return data; } }