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       目前常见的智能IC卡运行着JavaCard虚拟机，智能IC卡上可以运行由精简后的Java语言编写的卡应用（简称Applet）。智能IC卡的Applet不能自己启动，必须由外部终端（例如POS机，地铁刷卡终端等）向卡片发送Select命令，由此选中卡片的Applet，Applet才能运行。Appplet侧重于数据的处理，没有花销的I/O功能。Applet的程序有生命周期和指定入口，其中最主要的几个方法如下：

接下来贴段简单的Applet 源码，下载地址：http://download.csdn.net/detail/hellogv/8090041。

大概的思路是：Applet定义了2个开头标识皆为CMD_CLA的自定义命令CMD_INS_1和CMD_INS_2，当Android手机通过NFC分别发送CMD_INS_1和CMD_INS_2，Applet分别返回strHello和strWorld。

核心源码如下：

public class mytest extends Applet {private static final byte[] strHello= { (byte) 'H', (byte) 'e',(byte) 'l', (byte) 'l', (byte) 'o'};private static final byte[] strWorld = {(byte) 'W',(byte) 'o', (byte) 'r', (byte) 'l', (byte) 'd', };private static final byte CMD_CLA = (byte) 0x80;private static final byte CMD_INS_1 = (byte) 0x10;private static final byte CMD_INS_2 = (byte) 0x20;public static void install(byte[] bArray, short bOffset, byte bLength) {// GP-compliant JavaCard applet registrationnew mytest().register(bArray, (short) (bOffset + 1), bArray[bOffset]);}/** 当Java卡Applet被选中时，由JCRE调用。Java卡Applet可以定义select()完成初始化，* 否则，JCRE调用父类的select()。* @see javacard.framework.Applet#select()*/public boolean select() {short debug=100;debug++;//用于断点调试，当被select时触发。return super.select();}/** 当Java卡Applet被放弃时，由JCRE调用。Java卡Applet可以定义deselect()完成清除，* 否则，JCRE调用父类的deselect()。* @see javacard.framework.Applet#deselect()*/public void deselect() {short debug=100;debug++;//用于断点调试super.deselect();}/** 每次收到APDU命令，都会执行* @see javacard.framework.Applet#process(javacard.framework.APDU)*/public void process(APDU apdu) {if (selectingApplet()) {return;}//获取外部终端发过来的数据byte[] buffer = apdu.getBuffer();//获取第一位数据byte CLA = (byte) (buffer[ISO7816.OFFSET_CLA] & 0xFF);//获取第二位数据byte INS = (byte) (buffer[ISO7816.OFFSET_INS] & 0xFF);if (CLA != CMD_CLA) {//格式不对ISOException.throwIt(ISO7816.SW_CLA_NOT_SUPPORTED);}switch (INS) {case CMD_INS_1:sendBytes(apdu,strHello);break;case CMD_INS_2:sendBytes(apdu,strWorld);break;default:ISOException.throwIt(ISO7816.SW_INS_NOT_SUPPORTED);}}private void sendBytes(APDU apdu,byte[] arrays) {byte[] buffer = apdu.getBuffer();short length = (short) arrays.length;Util.arrayCopyNonAtomic(arrays, (short) 0, buffer, (short) 0,(short) length);apdu.setOutgoingAndSend((short) 0, length);}
}

接下来贴出Android端的核心代码，下载地址：http://download.csdn.net/detail/hellogv/8090053。

大概的思路是：Android端的NFC读写程序定义1个Applet的ID（AID），SELECT命令的报文头（SELECT_APDU_HEADER），2个自定义命令CMD_INS_1和CMD_INS_2。首先使用AID和SELECT_APDU_HEADER生成完整的SELECT命令，transceive（发送）到卡片，用于启动卡片里的AID对应的Applet。启动卡片里的Applet后，NFC读写程序发送SAMPLE_COMMAND里面的2条自定义命令，Applet分别返回"Hello""World"。

核心源码如下：

public final class CardReader {private static final String TAG = "LoyaltyCardReader";// AID for our loyalty card service.private static final String SAMPLE_CARD_AID = "1122001122";// 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};//自定义的命令private static final String[] SAMPLE_COMMAND={"8010000000",//卡片收到后返回"Hello""8020000000"};//卡片收到后返回"World"public static String[][] TECHLISTS;public static IntentFilter[] FILTERS;static {try {//the tech lists used to perform matching for dispatching of the ACTION_TECH_DISCOVERED intentTECHLISTS = new String[][] { { IsoDep.class.getName() }};FILTERS = new IntentFilter[] { new IntentFilter(NfcAdapter.ACTION_TECH_DISCOVERED, "*/*") };} catch (Exception e) {}}static public String tagDiscovered(Tag tag) {Log.e(TAG, "New tag discovered");String strResult="";IsoDep isoDep = IsoDep.get(tag);if (isoDep != null) {try {// Connect to the remote NFC deviceisoDep.connect();//发送select 命令,卡片会返回SELECT_OK_SW（90 00）byte[] cmdSelect = BuildSelectApdu(SAMPLE_CARD_AID);Log.e(TAG, "Sending: " + ByteArrayToHexString(cmdSelect));byte[] result = isoDep.transceive(cmdSelect);Log.e(TAG, "Receive: " + ByteArrayToHexString(result));byte[][] response = getResponse(result);byte[] statusWord =response[0];if (Arrays.equals(SELECT_OK_SW, statusWord) == false)return "";//循环发送自定义命令for(int i=0;i<SAMPLE_COMMAND.length;i++){String command = SAMPLE_COMMAND[i];result = HexStringToByteArray(command);Log.e(TAG, "Sending: " + command);result = isoDep.transceive(result);Log.e(TAG, "Receive: " + ByteArrayToHexString(result));response = getResponse(result);byte[] body =response[1];strResult=strResult+new String(body)+":"+ByteArrayToHexString(body)+"\r\n";}return strResult;} catch (IOException e) {Log.e(TAG, "Error communicating with card: " + e.toString());}}return null;}/**** 分解卡片返回的数据* @param b* @return [0]表示返回的状态值，[1]表示返回的正文*/private static byte[][] getResponse(byte[] b){byte[][] result = new byte[2][];int length = b.length;byte[] status = { b[length - 2],b[length - 1] };byte[] body = Arrays.copyOf(b, length - 2);result[0]=status;result[1]=body;return result;}public static String load(Parcelable parcelable) {// 从Parcelable筛选出各类NFC标准数据final Tag tag = (Tag) parcelable;return tagDiscovered(tag);}/*** 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;}
}