UDP 数据报已发送但从未收到

Question

我为客户端和服务器做了两个不同的 java 类，每个都有发送和接收方法。根据任务，我必须通过 DatagramPacket 建立服务器到客户端的连接，通过 DatagramChannel 建立客户端到服务器的连接。最后一个效果很好，但我在处理数据报时遇到了麻烦——它们是从服务器发送的，从未在客户端接收过。怎么了？

public class TransferClient implements Serializable{
    private static final long serialVersionUID = 26L;
    public TransferClient() {

    }

    public void send(Command com) throws IOException {
        SocketAddress socketAddressChannel = new InetSocketAddress("localhost", 1);
        DatagramChannel datagramChannel=DatagramChannel.open();
        ByteBuffer bb;
        datagramChannel.connect(socketAddressChannel);
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(baos);
        oos.writeObject(com);
        oos.flush();
        bb=ByteBuffer.wrap(baos.toByteArray(),0, baos.size());
        datagramChannel.send(bb,socketAddressChannel);
        baos.close();
        oos.close();
    }

    public Command receive() throws IOException, ClassNotFoundException {
        SocketAddress address = new InetSocketAddress(2029);
        DatagramSocket s = new DatagramSocket();
        DatagramPacket inputPacket = new DatagramPacket(new byte[1024],1024, address);
        s.receive(inputPacket);
        ByteArrayInputStream bais = new ByteArrayInputStream(inputPacket.getData());
        ObjectInputStream ois = new ObjectInputStream(bais);
        return (Command) ois.readObject();
    }
}

public class TransferServer {
    public TransferServer(){

    }

    public void send(Command com) throws IOException {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(baos);
        byte[] buffer;
        oos.writeObject(com);
        oos.flush();
        buffer=baos.toByteArray();
        SocketAddress address = new InetSocketAddress("localhost",2029);
        DatagramSocket s = new DatagramSocket();
        DatagramPacket outputPacket = new DatagramPacket(buffer,buffer.length,address);
        s.send(outputPacket);
    }


    public Command receive() throws IOException, ClassNotFoundException {
            SocketAddress socketAddressChannel = new InetSocketAddress("localhost", 1);
            DatagramChannel datagramChannel = DatagramChannel.open();
            datagramChannel.bind(socketAddressChannel);
            ByteBuffer bb = ByteBuffer.allocate(1024);
            datagramChannel.receive(bb);
            ByteArrayInputStream bais = new ByteArrayInputStream(bb.array());
            ObjectInputStream ois = new ObjectInputStream(bais);
            Command command;
            System.out.println(ois.available());
            command =(Command) ois.readObject();
            datagramChannel.close();
            ois.close();
            bais.close();
            return command;
    }
}

Answer 1

您必须指定绑定 DatagramSocket 的端口才能接收您的数据。否则它将绑定到您计算机上找到的第一个可用端口。

此处不需要SocketAddress，但需要考虑实际接收到的数据包长度。

见java.net.DatagramSocket Documentation

在你的 TransferClient class 的 receive() 方法中：

public Command receive() throws IOException, ClassNotFoundException {

    DatagramSocket s = new DatagramSocket(2029); //Add your port Here

    DatagramPacket inputPacket = new DatagramPacket(new byte[1024],1024);
    s.receive(inputPacket);
    ByteArrayInputStream bais = new ByteArrayInputStream(inputPacket.getData(), 0, packet.getLength());
    ObjectInputStream ois = new ObjectInputStream(bais);
    return (Command) ois.readObject();
}

UDP 数据报已发送但从未收到

UDP datagram is sent but never received

java

udp

datagram