通过UDP广播实现Android局域网Peer Discovering

try {       
Boolean endFlag = false;       
ServerSocket ss = new ServerSocket(12345);       
while (!endFlag) {           
// 等待客户端连接           
Socket s = ss.accept();           
BufferedReader input = new BufferedReader(newInputStreamReader(s.getInputStream()));           
//注意第二个参数据为true将会自动flush，否则需要需要手动操作output.flush()           
PrintWriter output = newPrintWriter(s.getOutputStream(),true);           
String message = input.readLine();           
Log.d("Tcp Demo", "message from Client:"+message);           
output.println("message received!");           
//output.flush();          
 if("shutDown".equals(message)){               
endFlag=true;          
 }           
s.close();       
}       
ss.close();  
} catch (UnknownHostException e) {       
e.printStackTrace();  
} catch (IOException e) {       
e.printStackTrace();  
}

try {       
Socket s = new Socket("localhost", 12345);       
// outgoing stream redirect to socket       
OutputStream out = s.getOutputStream();       
// 注意第二个参数据为true将会自动flush，否则需要需要手动操作out.flush()       
PrintWriter output = new PrintWriter(out, true);       
output.println("Hello World!");       
BufferedReader input = new BufferedReader(newInputStreamReader(s.getInputStream()));      
 // read line(s)       S
tring message = input.readLine();       
Log.d("Tcp Demo", "message From Server:" + message);       
s.close();  
} catch (UnknownHostException e) {       
e.printStackTrace();  
 } catch (IOException e) {       
e.printStackTrace();   }

// UDP服务器监听的端口  
Integer port = 12345;  
// 接收的字节大小，客户端发送的数据不能超过这个大小  
byte[] message = new byte[1024];  
try {       
// 建立Socket连接       
DatagramSocket datagramSocket = new DatagramSocket(port);       
DatagramPacket datagramPacket = new DatagramPacket(message, message.length);     
try {           
while (true) {               
// 准备接收数据               
datagramSocket.receive(datagramPacket);               
Log.d("UDP Demo", datagramPacket.getAddress()                       
.getHostAddress().toString()                       
+ ":" + new String(datagramPacket.getData()));          
 }       
} catch (IOException e) {           
e.printStackTrace();       
}  
} catch (SocketException e) {       
e.printStackTrace();   }
UDP客户端代码：
public static void send(String message) {       
message = (message == null ? "Hello IdeasAndroid!" : message);       
int server_port = 12345;       
DatagramSocket s = null;       
try {           
s = new DatagramSocket();       
} catch (SocketException e) {           
e.printStackTrace();       
}       
InetAddress local = null;       
try {           
// 换成服务器端IP           
local = InetAddress.getByName("localhost");      
} catch (UnknownHostException e) {           
e.printStackTrace();      
 }      
 int msg_length = message.length();       
byte[] messagemessageByte = message.getBytes();       
DatagramPacket p = new DatagramPacket(messageByte, msg_length, local,              
 server_port);       
try {           
s.send(p);      
 } catch (IOException e) {          
 e.printStackTrace();       
}  
}

while (true) {     
byte buf[] = new byte[1024];     
// 接收数据     
DatagramPacket packet = new DatagramPacket(buf, buf.length);     datagramSocket.receive(packet);     
String content = new String(packet.getData()).trim();     
// ……
 }

byte[] data = paramVarArgs[0].getBytes(); DatagramPacket dataPacket = new DatagramPacket(data,         
data.length, inetAddress, BROADCAST_PORT);
try {     
datagramSocket.send(dataPacket);
} catch (IOException e) {     
e.printStackTrace();     
return App.getInstance().getResources().getString(R.string.send_failed); }
 return App.getInstance().getResources().getString(R.string.send_success);

try {     
datagramSocket = new DatagramSocket();     
datagramSocket.setBroadcast(true); } 
catch (Exception e) {     
e.printStackTrace()
; }

// 获取本地所有网络接口
Enumeration<NetworkInterface> interfaces = NetworkInterface.getNetworkInterfaces();
while (interfaces.hasMoreElements()) {     
NetworkInterface networkInterface = interfaces.nextElement();     
if (networkInterface.isLoopback() || !networkInterface.isUp()) {         
continue;    
 }     
// getInterfaceAddresses()方法返回绑定到该网络接口的所有 IP 的集合     
for (InterfaceAddress interfaceAddress : networkInterface.getInterfaceAddresses()) {         InetAddress broadcast = interfaceAddress.getBroadcast();         /
/ 不广播回环网络接口         
if (broadcast  == null) {             
continue;        
 }         
// 发送广播报文         
try {             
DatagramPacket sendPacket = new DatagramPacket(data,                     
data.length, broadcast, BROADCAST_PORT);             
datagramSocket.send(sendPacket);         
} catch (Exception e) {             
e.printStackTrace();        
 }         
Log.d("发送请求", getClass().getName() + ">>> Request packet sent to: " +                 broadcast.getHostAddress() + "; Interface: " + networkInterface.getDisplayName());    
 }
}

try {     
handler = new ReceiveMsgHandler(this);     
new ServerSocket(handler).start(); } c
atch (IOException e) {     
e.printStackTrace()
; }

public ServerSocket(Handler handler) throws IOException {     
// Keep a socket open to listen to all the UDP trafic that is destined for this port     
datagramSocket = newDatagramSocket(BROADCAST_PORT,InetAddress.getByName("0.0.0.0")); datagramSocket.setBroadcast(true);     
// handler     
this.handler = handler;
}

while (true) {     
byte buf[] = new byte[1024];     
// 接收数据     
DatagramPacket packet = new DatagramPacket(buf, buf.length);     datagramSocket.receive(packet);     
String content = new String(packet.getData()).trim();     
if (content.equals("DISCOVER_REQUEST") &&             
!packet.getAddress().toString().equals("/" + IPUtil.getLocalIPAddress())) {         
byte[] feedback = "DISCOVER_RESPONSE".getBytes();        
 // 发送数据         
DatagramPacket sendPacket = new DatagramPacket(feedback, feedback.length,                 packet.getAddress(), BROADCAST_PORT);         
datagramSocket.send(sendPacket);         
// 发送Handler消息        
 sendHandlerMessage(packet.getAddress().toString());    
 } else if (content.equals("DISCOVER_RESPONSE") &&             !packet.getAddress().toString().equals("/" + IPUtil.getLocalIPAddress())) {         
// 发送Handler消息         
sendHandlerMessage(packet.getAddress().toString());    
 }
}

private ClientSocket() {     
try {        
 inetAddress = InetAddress.getByName(BROADCAST_IP);         
datagramSocket = new DatagramSocket();         
datagramSocket.setBroadcast(true);     
} catch (Exception e) {         
e.printStackTrace();

    }
 }

new AsyncTask<String, Integer, String>() {     
 @Override     
protected String doInBackground(String... paramVarArgs) {         
byte[] data = paramVarArgs[0].getBytes();         
DatagramPacket dataPacket = new DatagramPacket(data,                 
data.length, inetAddress, BROADCAST_PORT);         
try {             
datagramSocket.send(dataPacket);         
} catch (IOException e) {             
e.printStackTrace();             
return App.getInstance().getResources().getString(R.string.send_failed);        
 }         
return App.getInstance().getResources().getString(R.string.send_success);    
 }      
@Override     
protected void onPostExecute(String result) {         
super.onPostExecute(result);         
Message msg = new Message();         
msg.what = SendMsgHandler.STATUS;         
msg.obj = result;         
handler.sendMessage(msg);

  } 
}.execute(content);