java - Java DatagramSocket 向 255.255.255.255 发送数据包失败

Question

我正在用 java 编写网络程序，我想将一些数据包发送到 255.255.255.255，但它失败了，即使我将它们发送到 192.168.1.255，根据 ifconfig 命令的输出，它是广播地址。但是当我将它们发送到我伙伴的 IP 时，它工作正常。

这是我的程序的代码:

public class StackOverFlow {
    public static void main(String[] args) {
        Network net= new Network();

        Scanner input= new Scanner(System.in);
        while(input.hasNext())
          net.sendMessage(input.nextLine());
    }
}

我已经使用 DatagarmSocket 和 DatagramPacket 这样做了，这是我对网络的实现:

class Network {
DatagramSocket socket;

public Network() {
    try {
        socket = new DatagramSocket(8027);
        socket.connect(InetAddress.getByName("255.255.255.255"), 8027);
    } catch (Exception e) {
        System.err.println("Connection failed. " + e.getMessage());
    }
    listen();
}

public void listen() {
    new Thread() {
        public void run() {
            while (true) {
                try {
                    byte[] buf = new byte[1000];
                    DatagramPacket packet = new DatagramPacket(buf,
                            buf.length);
                    socket.receive(packet);
                    String message = new String(buf);
                    System.out.println("Recieved: " + message);
                    if (message.equals("end"))
                        return;
                } catch (Exception e) {
                    System.err.println(e.getMessage());
                }
            }
        }
    }.start();
}

public void sendMessage(String message){
    byte[] buf= message.getBytes();

    DatagramPacket packet= new DatagramPacket(buf, buf.length);
    try{
        socket.send(packet);
    }catch(Exception e){
        System.err.println("Sending failed. " + e.getMessage());
    }
}

没有异常被抛出。
我在一个临时网络中。
我使用的是 MAC OS X 10.6，而我的伙伴使用的是 kubuntu 11.04。 这是 ifconfig 输出:

lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
inet6 ::1 prefixlen 128 
inet6 fe80::1%lo0 prefixlen 64 scopeid 0x1 
inet 127.0.0.1 netmask 0xff000000 
gif0: flags=8010<POINTOPOINT,MULTICAST> mtu 1280
stf0: flags=0<> mtu 1280

en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
inet6 fe80::21f:f3ff:fed5:4779%en0 prefixlen 64 scopeid 0x4 
inet 192.168.1.1 netmask 0xffffff00 broadcast 192.168.1.255
ether 00:1f:f3:d5:47:79 
media: autoselect (100baseTX <full-duplex>) status: active
supported media: autoselect 10baseT/UTP <half-duplex> 10baseT/UTP <full-duplex> 10baseT/UTP     <full-duplex,hw-loopback> 10baseT/UTP <full-duplex,flow-control> 100baseTX <half-    duplex> 100baseTX <full-duplex> 100baseTX <full-duplex,hw-loopback> 100baseTX <full-duplex,flow-control> 1000baseT <full-duplex> 1000baseT <full-duplex,hw-loopback> 1000baseT <full-duplex,flow-control> none

en1: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
inet6 fe80::21d:4fff:feff:2b4d%en1 prefixlen 64 scopeid 0x5 
inet 213.233.170.97 netmask 0xfffffc00 broadcast 213.233.171.255
ether 00:1d:4f:ff:2b:4d 
media: autoselect status: active
supported media: autoselect

fw0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 2030
lladdr 00:21:e9:ff:fe:bc:79:b2 
media: autoselect <full-duplex> status: inactive
supported media: autoselect <full-duplex>

en2: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
ether 00:1f:f3:b6:2c:be 
media: autoselect status: inactive
supported media: none autoselect 10baseT/UTP <half-duplex>

vmnet1: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
inet 192.168.149.1 netmask 0xffffff00 broadcast 192.168.149.255
ether 00:50:56:c0:00:01 

vmnet8: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
inet 192.168.73.1 netmask 0xffffff00 broadcast 192.168.73.255
ether 00:50:56:c0:00:08 

en0 是我用来连接我伙伴的设备。

请简单点，我是新手:)

提前致谢。

Answer 1

使用广播时需要启用它

socket.setBroadcast(true);

另一件事是，如果两台计算机位于两个不同的网络中，则必须确保路由器配置正确。广播通常默认不被路由。此外，如果您的路由器具有无线接口(interface)和有线接口(interface)，如果未启用广播，这些广播也可能无法工作(默认情况下可能有硬件在这两个接口(interface)之间转发广播)。