Java TCP Client侦听和写入TCP Server

Question

我有一个用Java编写的TCP客户端和一个TCP服务器。 服务器正在等待客户端的指令，但是也应该能够将指令发送到客户端。 我可以使客户端向服务器发送一些内容并等待回复。 但是我不能让它像等待消息而不发送任何内容。

TCP客户端

    public class TCPClient {

    static DataOutputStream toServer;
    static BufferedReader fromServer;
    static Socket socket;

    public static void main(String[] args) throws Exception {
        BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
        System.out.println("*************************");
        System.out.println("*       Client          *");
        System.out.println("*************************");
        System.out.println("INSTRUCTION       | EFFECT");
        System.out.println("aktiv             | ready to do something");
        System.out.println("exit              | disconnect");
        System.out.println();
        System.out.print("Please enter the IP-Address of the Server: ");
        String ip = input.readLine();
        System.out.println();

        try {
            socket = new Socket(ip, 9999);
        } catch (Exception e) {
            System.out.println("Can not connect to Server!");
        }

        toServer = new DataOutputStream(socket.getOutputStream());  // Datastream FROM Server 
        fromServer = new BufferedReader(new InputStreamReader(socket.getInputStream()));     
        while (sendRequest()) {              
            receiveResponse();                 
        }
        socket.close();
        toServer.close();
        fromServer.close();
    }

    private static boolean sendRequest() throws IOException {
        BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
        String line;
        boolean holdTheLine = true;          // Connection exists

        System.out.print("> ");
        line = input.readLine();

        switch (line) {
            case "aktiv":
                toServer.writeBytes("active" + '\n');
                break;
            case "exit":
                holdTheLine = false;
                break;
            default:
                break;
        }

        return holdTheLine;
    }

    private static void receiveResponse() throws IOException {
        System.out.println("Server: " + fromServer.readLine() + '\n');
    }
}

TCP服务器

public class TCPServer {
    static boolean connected = true;
    public static void main(String[] args) throws Exception {
        System.out.println("********************************");
        System.out.println("*         Server               *");
        System.out.println("********************************");
        System.out.println("INSTRUCTION | EFFECT");
        System.out.println("ok          | send an ok to client");

        ServerSocket listenSocket = new ServerSocket(9999);

        while (true) {
            final Socket client = listenSocket.accept();

            Thread newClientThread = new Thread(new Runnable() {
                @Override
                public void run() {
                    multithreadedServer(client);
                }
            });
            newClientThread.start();
        }
    }

    public static void multithreadedServer(Socket client) {
        String line;
        final BufferedReader fromClient;
        final DataOutputStream toClient;
        Thread cmdForClient;

        try {
            fromClient = new BufferedReader(new InputStreamReader(client.getInputStream()));
            toClient = new DataOutputStream(client.getOutputStream());

            while (connected) {
                cmdForClient = new Thread(new Runnable() {
                    @Override
                    public void run() {
                        try {
                            String line = fromClient.readLine();
                            System.out.println("Client: " + line);
                            if (line.equals("exit")) {
                                connected = false;
                            }
                        } catch (Exception e) {
                            System.out.println(e);
                        }
                    }
                });
                cmdForClient.start();

                final BufferedReader input = new BufferedReader(new InputStreamReader(System.in));

                try {
                    String reply = input.readLine();
                    if (reply.equals("ok")) {
                            toClient.writeBytes("OK." + '\n');
                    }
                } catch (Exception e) {
                    System.out.println(e);
                }
            }
            fromClient.close();
            toClient.close();
            client.close();
        } catch (Exception e) {
            System.out.println(e);
        }
    }

}

Answer 1

客户端-服务器方案的典型操作是客户端将请求发送到服务器。 但是，在对等应用程序中，两个端点都可能同时充当客户端和服务器。 唯一的区别是哪个端点打开了连接。 在您的情况下，问题在于只有“服务器”正在使用接收器线程。 在客户端启动一个接收器线程，您的问题应该得到解决。 您应该几乎可以重用客户机中服务器中的线程代码。 打开服务器连接后，只需将套接字传递给接收线程即可。

编辑：

在您的客户中：

            Thread newServerThread = new Thread(new Runnable() {
                @Override
                public void run() {
                    multithreadedServer(socket);
                }
            });
            newServerThread.start();

其中socket是服务器的套接字。 您可能需要针对客户端操作的任何细节或差异更新multithreadedServer，但是原理应相同。