JAVA 网络编程(5) SOCKET UDP 单播和组播,以及组播其他机器收不到报文的解决方法

UDP既可以单播也可以组播

一，单播

单播的过程为

发送方：

InetAddress destAddr = InetAddress.getByName("192.168.4.199");// 发送的目的地址
int targetPort = 3001; // 发送的目的端口
DatagramSocket socket = new DatagramSocket();
byte[] b = “信息”.getBytes();
DatagramPacket pk = new DatagramPacket(b, b.length, destAddr, targetPort);
socket.send(pk);//发送

接收方：

int port = 3001;//接收数据包的IP端口
DatagramSocket socket = new DatagramSocket(port);
byte b[] = new byte[512];
DatagramPacket pack = new DatagramPacket(b, b.length);
socket.receive(pack);//接收信息
int length = pack.getLength();
String msg = new String(pack.getData(),0,length);
Logger.getGlobal().info(msg);

代码示例：

/** * 001 UDP单播发送，启动后在控制台输出 */public class SSend {public static void main(String[] args) throws SocketException, IOException {InetAddress destAddr = InetAddress.getByName("192.168.4.199");// 发送的目的地址int targetPort = 3001; // 发送的目的端口try (DatagramSocket socket = new DatagramSocket(); Scanner r = new Scanner(System.in);) {while (true) {String s = r.nextLine();byte[] b = s.getBytes();DatagramPacket pk = new DatagramPacket(b, b.length, destAddr, targetPort);socket.send(pk);//发送}} catch (Exception e) {e.printStackTrace();}}}

/** * 001 * UDP单播接收服务 */public class SReceive {public static void main(String[] args) throws UnknownHostException {int port = 3001;//接收数据包的IP端口try(DatagramSocket socket = new DatagramSocket(port);) {byte b[] = new byte[512];DatagramPacket pack = new DatagramPacket(b, b.length);while(socket!=null){socket.receive(pack);//接收信息int length = pack.getLength();String msg = new String(pack.getData(),0,length);Logger.getGlobal().info(msg);}} catch (Exception e) {e.printStackTrace();}}}

二，组播

组播使用D类地址，D类地址不会被写入IP报文的源地址IP

我们使用D类地址中的用户组播地(224.0.2.0~238.255.255.255)址来测试

发送方：

MulticastSocket socket = new MulticastSocket(2011);
InetAddress mcastaddr = InetAddress.getByName("224.116.8.0");
socket.joinGroup(mcastaddr);//加入 组播组
byte[] b = msg.getBytes();
DatagramPacket pack = new DatagramPacket(b, b.length, mcastaddr, port);
socket.send(pack);//组播发送 数据报，可被group成员接收到

接收方和发送方开始的代码类似，都是指定IP和端口，加入组播组：

InetAddress mcastaddr = InetAddress.getByName("224.116.8.0");
MulticastSocket socket = new MulticastSocket(port);
socket.joinGroup(mcastaddr);
byte b[] = new byte[512];
DatagramPacket pack = new DatagramPacket(b, b.length, mcastaddr, port);
socket.receive(pack);
String msg = new String(pack.getData(), 0, b.length);
Logger.getGlobal().info(msg);

示例代码：

/** * 002组播 输出接收到的字符串 */public class MReceive {public static void main(String[] args) {String host = "224.116.8.0";int port = 2011;try (MulticastSocket socket = new MulticastSocket(port);) {InetAddress mcastaddr = InetAddress.getByName(host);socket.joinGroup(mcastaddr);byte b[] = new byte[512];DatagramPacket pack = new DatagramPacket(b, b.length, mcastaddr, port);while (true) {socket.receive(pack);String msg = new String(pack.getData(), 0, b.length);Logger.getGlobal().info(msg);}} catch (Exception e) {e.printStackTrace();}}}<pre name="code" class="java">/** * 002 组播 */public class MSend {private static final SimpleDateFormat SDF = new SimpleDateFormat("yyyy-MM-dd-hh:mm:ss:SSS");// 显示日期格式public static void main(String[] args) {String host = "224.116.8.0";int port = 2011;Timer t = new Timer();t.schedule(new TimerTask() {@Overridepublic void run() {send(host, port, SDF.format(new Date()));}}, 0, 2000);}public static void send(String addr, int port, String msg) {try (MulticastSocket socket = new MulticastSocket(port);) {// TTL从字面上翻译，是可以存活的时间，但实际上TTL是IP数据包在计算机网络中可以转发的最大跳数,1为本地网络socket.setTimeToLive(1);InetAddress mcastaddr = InetAddress.getByName(addr);socket.joinGroup(mcastaddr);// 加入 组播组byte[] b = msg.getBytes();DatagramPacket pack = new DatagramPacket(b, b.length, mcastaddr, port);// 待发送数据包socket.send(pack);// 组播发送 数据报，可被group成员接收到} catch (Exception e) {e.printStackTrace();}}}

三，组播各个机器不互通的解决方法

由于单播是指定发送目的的IP和端口，所有只要能ping通对方的IP就能将单播的UDP报文发送过去。

但是对于组播，由于加入和发送的目的是D类地址，所以得保证各个机器之间是同一个网段

①禁止其他网卡，只保留一块网卡（我是将笔记本的无线网卡金庸，只用我的有线网卡），以及公司的台式机

②修改IP和网关，确认在同一网段

下面是我的电脑我另一台测试电脑的网络设置