Android发现局域网IP

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Android发现局域网IP的原理就在于通过udp向路由网关广播消息，然后监听对应的消息回复。示例代码如下：

1、获取udp广播地址

public static InetAddress getBroadcastAddress(Context pContext) throws UnknownHostException {    WifiManager cWifi = (WifiManager)pContext.getSystemService(Context.WIFI_SERVICE);    DhcpInfo cDhcp = cWifi.getDhcpInfo();    if(cDhcp==null) {        return InetAddress.getByName("255.255.255.255");    }    int cBroadcast = (cDhcp.ipAddress & cDhcp.netmask) | ~cDhcp.netmask;    byte[] cQuads = new byte[4];    for (int k = 0; k < 4; k++)    cQuads[k] = (byte) ((cBroadcast >> k * 8) & 0xFF);    return InetAddress.getByAddress(cQuads);}

2、根据广播地址创建udp发送和监听机制

public static DatagramSocket mSocket;public static DatagramPacket mPacket;

public static String startFind(InetAddress cAddr){String cIP = "";try {mSocket = new DatagramSocket(8000);mSocket.setBroadcast(true);byte[] cBuffer = "Hello World".getBytes();DatagramPacket cPacket = new DatagramPacket(cBuffer,cBuffer.length);cPacket.setAddress(cAddr);cPacket.setPort(9999);mSocket.send(cPacket);while(true){cIP = receiveData();if(null != cIP)break;}} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();cIP = null;}mSocket.close();return cIP;}
public static String receiveData(){byte[] cReceivedata = new byte[1024];DatagramPacket cPacket = new DatagramPacket(cReceivedata,cReceivedata.length);cPacket.getAddress();try{if (mSocket == null){Log.e("dataSocket", "null");}mSocket.receive(cPacket);}catch(IOException e){e.printStackTrace();}if(0 != cPacket.getLength()){String cCheck = new String(cReceivedata,0,cPacket.getLength());Log.i("findIP", cCheck);if(cCheck.equals("HelloWorldACK")){Log.i("findIP", cPacket.getAddress().getHostAddress());return cPacket.getAddress().getHostAddress();}}return null;}
注意：在Android中不能在app主线程中进行socket资源的动作，至于原因，相信会android的人都知道

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