java - 如何在java nio中创建多个监听同一端口的udp客户端？

Question

对于普通的io，我可以这样做:

s1=new DatagramSocket(1234)
s2=new DatagramSocket(1234)

bytes=xxxxxx
packet = DatagramPacket(bytes, bytes.size,InetSocketAddress("localhost",1234))
new DatagramSocket().send(packet)
//  and then the s1 and s2 can receive the packet.

但在蔚来。这个怎么做？我尝试过这样的:

第一:

s1=DatagramChannel.open()
s1.bind(new Inetsocketaddress("localhost",1234)

s2=DatagramChannel.open()
s2.bind(new Inetsocketaddress("localhost",1234)// will throw an exception

第二个:

s1=DatagramChannel.open()
s1.setOption(StandardSocketOptions.SO_REUSEADDR, true);
s1.bind(new Inetsocketaddress("localhost",1234)

s2=DatagramChannel.open()
s2.setOption(StandardSocketOptions.SO_REUSEADDR, true);
s2.bind(new Inetsocketaddress("localhost",1234)

//these code will not throw exception. but s2 cannot receive any data.
// when i close s1,  then s2 will receive data.

Answer 1

如果您确实需要所有客户端都处理消息，则需要多播/广播协议(protocol)。从这个意义上说，正如上一个问题( Does Java NIO support broadcast or multicast? )中所述，NIO2 支持多播和广播，但不使用 DatagramChannel 类。相反，您拥有 MultiCastChannel 接口(interface)(您可以在 http://javanio.info/filearea/nioserver/WhatsNewNIO2.pdf 中找到官方文档，并在 How do I implement a multicast client in NIO.2? 中找到示例)。关于您的代码，它应该如下所示:

   NetworkInterface netInterface = NetworkInterface.getByName("em1");
   InetAddress group = InetAddress.getByName("localhost");

   // Reader 1
   System.out.println("Create Reader 1");
   DatagramChannel s1 = DatagramChannel.open(StandardProtocolFamily.INET);
   s1.setOption(StandardSocketOptions.SO_REUSEADDR, true);
   s1.bind(new InetSocketAddress(PORT));
   s1.setOption(StandardSocketOptions.IP_MULTICAST_IF, netInterface);

   // Reader 2
   System.out.println("Create Reader 2");
   DatagramChannel s2 = DatagramChannel.open(StandardProtocolFamily.INET);
   s2.setOption(StandardSocketOptions.SO_REUSEADDR, true);
   s2.bind(new InetSocketAddress(PORT));
   s2.setOption(StandardSocketOptions.IP_MULTICAST_IF, netInterface);

请注意，您的底层硬件堆栈必须支持多播/广播。否则，join 方法将抛出异常。

如果您不需要所有客户端都处理该消息，而是需要其中任何客户端处理该消息而不阻塞其他客户端，则可以设置非阻塞套接字选项。考虑到您提供的代码，我在下面添加了一个非阻塞的解决方案:

import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.StandardSocketOptions;
import java.nio.ByteBuffer;
import java.nio.channels.DatagramChannel;
import java.nio.charset.StandardCharsets;


public class Main {

    private static final String HOST = "localhost";
    private static final int PORT = 1234;

    private static final String MESSAGE = "HelloWorld";
    private static final int MESSAGE_SIZE = MESSAGE.length();


    public static void main(String[] args) throws IOException {
        // Reader 1
        System.out.println("Create Reader 1");
        DatagramChannel s1 = DatagramChannel.open();
        s1.configureBlocking(false);
        s1.setOption(StandardSocketOptions.SO_REUSEADDR, true);
        s1.bind(new InetSocketAddress(HOST, PORT));

        // Reader 2
        System.out.println("Create Reader 2");
        DatagramChannel s2 = DatagramChannel.open();
        s2.configureBlocking(false);
        s2.setOption(StandardSocketOptions.SO_REUSEADDR, true);
        s2.bind(new InetSocketAddress(HOST, PORT));

        // Writer
        System.out.println("Create Writer");
        DatagramChannel s3 = DatagramChannel.open();

        // Send and receive messages
        System.out.println("Send message");
        send(s3);
        System.out.println("Receive message on Reader 1");
        receive(s1);
        System.out.println("Receive message on Reader 2");
        receive(s2);

        // Close
        System.out.println("Close");
        s1.close();
        s2.close();
        s3.close();
    }

    private static void send(DatagramChannel channel) throws IOException {
        ByteBuffer buf = ByteBuffer.allocate(MESSAGE_SIZE);
        buf.clear();
        buf.put(MESSAGE.getBytes());
        buf.flip();

        int bytesSent = channel.send(buf, new InetSocketAddress(HOST, PORT));
        System.out.println("Sent: " + bytesSent);
    }

    private static void receive(DatagramChannel channel) throws IOException {
        ByteBuffer buf = ByteBuffer.allocate(MESSAGE_SIZE);
        buf.clear();

        channel.receive(buf);

        String str = new String(buf.array(), StandardCharsets.UTF_8);
        System.out.println("Received: " + str);
    }

}

输出是:

Create Reader 1
Create Reader 2
Create Writer
Send message
Sent: 10
Receive message on Reader 1
Received: 
Receive message on Reader 2
Received: HelloWorld
Close