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
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