之前我的一篇文章《网络唤醒全攻略(Wake On Lan)》介绍过如何设置远程唤醒电脑，着重于使用，这篇主要从原理方面解析一下当中的奥妙；
原理
将唤醒魔术包发送的被唤醒机器的网卡上，魔术包指AMD公司开发的唤醒数据包，具有远程唤醒的网卡都支持这个标准，用16进制表示如下：
6对“FF”前缀+16次重复MAC地址,举个例子假如我的网卡MAC地址是：AA:BB:CC:DD:EE:FF:11
那么魔术包就是:
0xFFFFFFFFFFAABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11AABBCCDDEEFF11
但是传送的时候必须封包成二进制格式才可以传送，简单来说，我们抽2个区段分析：
FFFFFFFFFFF 转成： 11111111 11111111 11111111 11111111 11111111 11111111
AABBCCDDEEFF11 转成：10101010 10111011 11001100 11011101 11101110 11111111 00010001
那么封包后就是把每个字节连接在一起：
11111111 11111111 11111111 11111111 11111111 11111111 10101010 10111011 11001100 11011101 11101110 11111111 00010001
……..10101010 10111011 11001100 11011101 11101110 11111111 00010001（第16次）
开发实现
关键代码（Java）:
private String Wake(String name, String host, String mac, int port) {
try {
byte[] macBytes = getMacBytes(mac);//转成字节类型
byte[] bytes = new byte[6 + 16 * macBytes.length];
for (int i = 0; i < 6; i++) {
bytes[i] = (byte) 0xff;
}
for (int i = 6; i < bytes.length; i += macBytes.length) {
System.arraycopy(macBytes, 0, bytes, i, macBytes.length); //放入16个MAC地址
}
InetAddress address = InetAddress.getByName(host);
DatagramPacket packet = new DatagramPacket(bytes, bytes.length, address, port);
DatagramSocket socket = new DatagramSocket();
socket.send(packet);
socket.close();
return "wol_package_sent_success";
} catch (Exception e) {
return "wol_package_sent_fail";
}
}
private static byte[] getMacBytes(String mac) throws IllegalArgumentException {
byte[] bytes = new byte[6];
String[] hex = mac.split("(\\:|\\-)");
if (hex.length != 6) {
throw new IllegalArgumentException("Invalid MAC address.");
}
try {
for (int i = 0; i < 6; i++) {
bytes[i] = (byte) Integer.parseInt(hex[i], 16);
}
} catch (NumberFormatException e) {
throw new IllegalArgumentException("Invalid hex digit in MAC address.");
}
return bytes;
}
更多细节请 阅读原文