java - 无法让Java和C#通过socket进行通信

Question

我一直在尝试创建一个可以一起通信的 Java 和 C# 应用程序。在这种情况下，用户从C#端发送String，它应该显示在Java控制台上并回显。不幸的是，我只能建立连接，而无法发送或接收任何内容。

Java代码片段:

public CommunicationThreadHandler(Socket socket, CarList carList) {
    this.socket = socket;
    this.carList = carList;
    try {
        this.in = new DataInputStream(socket.getInputStream());
        this.out = new DataOutputStream(socket.getOutputStream());
        this.writer = new Writer(out);
    } catch (IOException e) {
        System.out.println("Exception when reading or receiving data!");
        e.printStackTrace();
    }
    this.ip = socket.getRemoteSocketAddress().toString();
}

@Override
public void run() {
    while (true) {
        try {
            Gson gson = new Gson();
            String msgJson = in.readUTF();
            String msg = gson.fromJson(msgJson,String.class);
            System.out.println("Message from C# client: "+msg);
            String reply = "Server echo: "+msg;
            String replyJson = gson.toJson(reply);
            out.writeUTF(replyJson);
            if (msg.equals(Package.EXIT))
                break;
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

C# 代码片段:

public static void StartClient()
{
    // Data buffer for incoming data.  
    byte[] bytes = new byte[1024];

    // Connect to a remote device.  
    try
    {
        // Establish the remote endpoint for the socket.  
        // This example uses port 11000 on the local computer.  
        IPHostEntry ipHostInfo = Dns.GetHostEntry(Dns.GetHostName());
        IPAddress ipAddress = ipHostInfo.AddressList[0];
        IPEndPoint remoteEP = new IPEndPoint(ipAddress, 11000);

        // Create a TCP/IP  socket.  
        Socket sender = new Socket(ipAddress.AddressFamily,
            SocketType.Stream, ProtocolType.Tcp);

        // Connect the socket to the remote endpoint. Catch any errors.  
        try
        { 
            sender.Connect(remoteEP);

            Console.WriteLine("Socket connected to {0}",
                sender.RemoteEndPoint.ToString());
            while (true)
            {
                Console.Write("Enter message to server: ");

                string message = Console.ReadLine();
                Console.WriteLine($"To be sent: {message}");

                // Encode the data string into a byte array.  
                byte[] msg = Encoding.ASCII.GetBytes(message);

                // Send the data through the socket.  
                int bytesSent = sender.Send(msg);

                // Receive the response from the remote device.  
                int bytesRec = sender.Receive(bytes);

                string msgFromServer = Encoding.ASCII.GetString(bytes, 0, bytesRec);

                if (msgFromServer.Equals("EXIT"))
                    break;

                Console.WriteLine($"Server says: {msgFromServer}");
            }
            // Release the socket.

            sender.Shutdown(SocketShutdown.Both);
            sender.Close();

        }

Answer 1

您的问题是您在 Java 中使用 DataInputStream/DataOutputStream，它们使用 Java 特定的、类似 XDR 的数据类型序列化协议(protocol)。您没有在 C# 端使用该协议(protocol)。

切换到使用原始输入/输出流应该足够了(尽管很脆弱)。但是，请注意，当您从 C# 发送原始字节时，收件人无法得知消息何时完成。最好发送消息的字节数，然后发送实际消息(这就是 DataInputStream/DataOutputStream 所做的，但它还需要考虑其他注意事项需要在 C# 端正确实现，例如 readUTF/writeUTF 使用“修改的 UTF-8”格式而不是普通的 UTF-8。

现在的问题是，您从 C# 发送原始字节，readUTF() 方法读取前两个字节作为长度，然后尝试读取该长度的消息。例如，如果C#发送“Hello”(编码为0x48、0x65、0x6c、0x6c、0x6f)，那么Java端将读取0x48、0x65(“He”)作为“消息长度为18533”，然后尝试读取18533字节，而实际剩余字节只有 3 个(“llo”)。这会导致输入阻塞，等待剩余的 18530 字节，而这些字节永远不会到达。