目前NFC应用的大的框架上的理解：
使用API LEVEL 19及以上，支持的API有三个：
android.nfc,android.nfc.cardemulator,android.nfc.tech
NFC在手机上的应用大体分为两类：读卡器和卡
android.nfc.cardemulator接口是为NFC作为卡应用提供的接口，在较低版本的API上是没有的android.nfc.tech，android.nfc接口是为NFC作为读卡器应用提供的接口
NFC数据过滤
NFC有三种过滤器分别是ACTION_NDEF_DISCOVERED，ACTION_TECH_DISCOVERED，ACTION_TAG_DISCOVERED。
1. ACTION_NDEF_DISCOVERED
当扫描到的tag中包含有NDEF载荷且为已知类型，该intent将用来启动Activity。该intent的优先级最高，tag分发系统总是先于其他intent用该intent来启动Activity。
2. ACTION_TECH_DISCOVERED
如果manifest中没有注册处理ACTION_NDEF_DISCOVERED类型的intent，该intent将被用以启动Activity。如果tag中没有包含可以映射到MIME或者URI类型的数据，或者虽然没有包含NDEF数据，但是已知的tag技术，则该intent也会被直接启用。
3. ACTION_TAG_DISCOVERED
如果以上两个intent都没人疼，那么该intent就会启动。
过滤器的作用是过滤掉杂质，剩下的就是我们需要的了。这三种过滤方式可同时配置，可以比方成从上到下三层，只要是符合某一层过滤器要求的，过滤完就停止往下一层。
本案例使用ACTION_TECH_DISCOVERED
读卡器实现
代码实现：
AndroidManifest.xml 中 配置activity，因为作为读卡器实现的话，需要监听intent
<activity android:name=".MainActivity" android:label="@string/app_name" android:launchMode="singleTop"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> <!-- NFC-related intent filter. Allows application to handle messages from any NFC-A devices discovered. Other Android devices are required to support NFC-A. See: res/xml/nfc_tech_filter.xml --> <intent-filter> <action android:name="android.nfc.action.TECH_DISCOVERED" /> </intent-filter> <meta-data android:name="android.nfc.action.TECH_DISCOVERED" android:resource="@xml/nfc_tech_filter" /></activity>
res/xml/nfc_tech_filter.xml 中配置tech-list
<?xml version="1.0" encoding="utf-8"?><!-- This file is used as part of the filter for incoming NFC TECH_DISCOVERED intents. --><resources xmlns:android="http://schemas.android.com/apk/res/android"> <!-- Android's host card emulation feature only supports the IsoDep protocol. --> <tech-list> <tech>android.nfc.tech.IsoDep</tech> </tech-list></resources>
配置文件完成后编写activity的处理方法：主要是enable disable NFC的ReaderMode
public static int READER_FLAGS =
NfcAdapter.FLAG_READER_NFC_A | NfcAdapter.FLAG_READER_SKIP_NDEF_CHECK;
public LoyaltyCardReader mLoyaltyCardReader;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mLoyaltyCardReader = new LoyaltyCardReader(this);
// Disable Android Beam and register our card reader callback
enableReaderMode();
}
@Override
public void onPause() {
super.onPause();
disableReaderMode();
}
@Override
public void onResume() {
super.onResume();
enableReaderMode();
}
private void enableReaderMode() {
Log.i(TAG, "Enabling reader mode");
NfcAdapter nfc = NfcAdapter.getDefaultAdapter(activity);
if (nfc != null) {
nfc.enableReaderMode(activity, mLoyaltyCardReader, READER_FLAGS, null);
}
}
private void disableReaderMode() {
Log.i(TAG, "Disabling reader mode");
NfcAdapter nfc = NfcAdapter.getDefaultAdapter(activity);
if (nfc != null) {
nfc.disableReaderMode(activity);
}
}
当TECH_DICOVERED触发时，LoyaltyCardReader的onTagDiscovered，通过tag获取到对应的IsoDep
IsoDep isoDep = IsoDep.get(tag);
后续就可以通过IsoDep跟卡端建立通讯连接，连接建立的最重要信息时aid
LoyaltyCardReader实现代码：
package com.example.android.cardreader;import android.nfc.NfcAdapter;import android.nfc.Tag;import android.nfc.tech.IsoDep;import com.example.android.common.logger.Log;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. * <p> * 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"; // Format: [Class | Instruction | Parameter 1 | Parameter 2] private static final String GET_DATA_APDU_HEADER = "00CA0000"; // "OK" status word sent in response to SELECT AID command (0x9000) private static final byte[] SELECT_OK_SW = {(byte) 0x90, (byte) 0x00}; private static final String WRITE_DATA_APDU_HEADER = "00DA0000"; private static final String READ_DATA_APDU_HEADER = "00EA0000"; private static final byte[] WRITE_DATA_APDU = BuildWriteDataApdu(); private static final byte[] READ_DATA_APDU = BuildReadDataApdu(); // 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(); Log.i(TAG, "Timeout = " + isoDep.getTimeout()); isoDep.setTimeout(3600); Log.i(TAG, "Timeout = " + isoDep.getTimeout()); Log.i(TAG, "MaxTransceiveLength = " + isoDep.getMaxTransceiveLength()); // 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[] selCommand = BuildSelectApdu(SAMPLE_LOYALTY_CARD_AID); // Send command to remote device Log.i(TAG, "Sending: " + ByteArrayToHexString(selCommand)); byte[] result = isoDep.transceive(selCommand); // 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)) { String accountNumber = new String(payload, "UTF-8"); Log.i(TAG, "Received: " + accountNumber); //todo test sample setAPDUMsg(isoDep,"test"); getAPDUMsg(isoDep); } } 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); } /** * Build APDU for GET_DATA command. See ISO 7816-4. * * @return APDU for SELECT AID command */ public static byte[] BuildGetDataApdu() { // Format: [CLASS | INSTRUCTION | PARAMETER 1 | PARAMETER 2 | LENGTH | DATA] return HexStringToByteArray(GET_DATA_APDU_HEADER + "0FFF"); } /** * 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; } public static byte[] BuildWriteDataApdu() { // Format: [CLASS | INSTRUCTION | PARAMETER 1 | PARAMETER 2 | LENGTH | DATA] return HexStringToByteArray(WRITE_DATA_APDU_HEADER + "0FFF"); } public static byte[] BuildReadDataApdu() { // Format: [CLASS | INSTRUCTION | PARAMETER 1 | PARAMETER 2 | LENGTH | DATA] return HexStringToByteArray(READ_DATA_APDU_HEADER + "0FFF"); } public static byte[] ConcatArrays(byte[] first, byte[]... rest) { int totalLength = first.length; for (byte[] array : rest) { totalLength += array.length; } byte[] result = Arrays.copyOf(first, totalLength); int offset = first.length; for (byte[] array : rest) { System.arraycopy(array, 0, result, offset, array.length); offset += array.length; } return result; } private String getAPDUMsg(IsoDep isoDep) { if (isoDep == null) { return ""; } String msg = null; try { Log.i(TAG, "Sending: " + ByteArrayToHexString(READ_DATA_APDU)); byte[] result = isoDep.transceive(READ_DATA_APDU); 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)) { msg = new String(payload, "UTF-8"); Log.i(TAG, "Received msg: " + msg); } } catch (Exception e) { Log.w(TAG, "getAPDUMsg Exception:" + e); } return msg; } private void setAPDUMsg(IsoDep isoDep, String msg) { if (isoDep == null) { return; } try { Log.i(TAG, "write: " + WRITE_DATA_APDU_HEADER); byte[] selCommand = ConcatArrays(WRITE_DATA_APDU, msg.getBytes()); Log.i(TAG, "Sending: " + ByteArrayToHexString(selCommand)); byte[] result = isoDep.transceive(selCommand); int resultLength = result.length; byte[] statusWord = {result[resultLength - 2], result[resultLength - 1]}; byte[] payload1 = 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(payload1, "UTF-8"); Log.i(TAG, "Received payload: " + accountNumber); } } catch (Exception e) { Log.w(TAG, "setAPDUMsg Exception:" + e); } return; }}
简单地说：
1、CardReader使用SAMPLE_LOYALTY_CARD_AID + SELECT_APDU_HEADER 生成 SELECT APDU;
2、CardReader发送SELECT APDU到CardEmulation后，CardEmulation返回SELECT_OK_SW + accountNumber。
其中SAMPLE_LOYALTY_CARD_AID ，SELECT_APDU_HEADER ，SELECT_OK_SW 都必须是CardReader与CardEmulation双方定义好的。
另外，CardReader在4.4和4.4以下系统的用法也略有不同，4.4以下系统用onNewIntent（），4.4系统就要通过enableReaderMode（）方法，如果4.4系统用onNewIntent（）的话，会导致一直P2P，而不是卡与读卡器的关系。
demo:git@github.com:zhan3080/NfcHCE-Reader-Emulation.git
参考链接：
https://blog.csdn.net/demon_w/article/details/50174737
https://blog.csdn.net/okletsgo007/article/details/46727831
apdu指令
https://blog.csdn.net/wwt18811707971/article/details/85785354
https://blog.csdn.net/qq_36135335/article/details/82463179