Java中简单客户端-服务器应用程序的读/写

Question

我是Java的新手，我正在尝试学习线程和套接字。所以决定按照官方的java教程制作简单的客户机-服务器应用程序。我的想法很简单--服务器等待连接，如果出现，它就用新的套接字、输入和输出生成新线程。客户端->建立连接；带有套接字、输入、输出和stdIn的新线程（读取行，然后发送到服务器）。但是我的代码出了点问题（不知道为什么）。连接已经建立，没有例外。谁能解释一下为什么不工作，如何修复它？您还可以对代码有什么建议吗（可能不是关于最佳实践之类的）：

Client side:

public class Client {
    private BufferedReader reader;
    private Socket sock;
    private PrintWriter writer;

public static void main(String[] args) {
    Client client = new Client();
    client.go();
}

public void go() {
    setUpNetworking();

}

private void setUpNetworking() {
    try{
        sock = new Socket("127.0.0.1", 5000);
        System.out.println("Network established");

        ServerThread serverThread= new ServerThread(sock);
        serverThread.start();

        System.out.println("Type your message: ");
    } catch (IOException e) {
        System.out.println("Problem with establishing the network: " + e);
    }
}

class ServerThread extends Thread {
    Socket socket;
    PrintWriter out;
    BufferedReader in;
    BufferedReader stdIn;

    ServerThread(Socket socket) {
        this.socket = socket;

        try{
            out = new PrintWriter(socket.getOutputStream());
            in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            stdIn = new BufferedReader(new InputStreamReader(System.in));
        }catch (IOException e) {
            System.out.println("Problem with trying to read/write to server: " + e);
        }
    }
    @Override
    public void run() {
        String fromServer;
        String fromClient;
        while(true){
            try{

                if((fromServer = in.readLine()) != null) System.out.println(" " + fromServer);
                else if((fromClient = stdIn.readLine()) != null) out.println(fromClient);

            }catch(Exception e) {
                System.out.println("msg exception: " + e);
            }

        }
    }
}

}

服务器端：

public class Server {
    //Run server until keepGoing = false
    private boolean keepGoing = true;



    public static void main(String[] args) {
        Server server = new Server();
        server.go();
    }

    public void go() {

            try {
                ServerSocket serverSocket = new ServerSocket(5000);

                while(keepGoing) {

                    Socket clientSocket = serverSocket.accept();
                    ClientThread t = new ClientThread(clientSocket);
                    t.start();
                }
            } catch (IOException e) {
                System.out.println("Problem with socket/network: " + e);
            }
    }

    class ClientThread extends Thread {
        Socket clientSocket;
        PrintWriter out;
        BufferedReader in;

        ClientThread(Socket clientSocket) {
            this.clientSocket = clientSocket;

            try{
                out = new PrintWriter(clientSocket.getOutputStream());
                in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
            } catch (IOException e) {
                System.out.println("Problem with creating in/out: " + e);
            }
        }

        @Override
        public void run() {
            String message;
            while(keepGoing) {
                try{
                    message = in.readLine();
                    out.println(message);
                    System.out.println(message);

                } catch (IOException e){
                    System.out.println("Exception while try to read line: " + e);
                }

            }
        }
    }

}

PS我对代码做了一点改动--没有创建ClientThread类，而是创建了新的runnable类，并将该变量传递给thread类。受到这个问题的启发：“implements runnable”vs.“extends thread”。

Answer 1

我认为问题是服务器端和客户端都在等待任何输入。服务器：

message = in.readLine();

客户：

if((fromServer = in.readLine()) != null)
   System.out.println(" " + fromServer);
else if((fromClient = stdIn.readLine()) != null)
   out.println(fromClient);

但是客户机代码已经阻塞在fromserver=in.readline()部分上，因此它永远无法读取标准输入，因此不会向服务器发送任何内容。

BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
String read = "";
do {
    read = stdIn.readLine();
    System.out.println("Read from stdin: " + read);
    serverThread.send(read);

}
while (!read.equals("exit"));

void send(String string) {
    System.out.println("Sending to server: " + string);
    out.println(string);
}

out = new PrintWriter(socket.getOutputStream(), true);

然而，这只是第一步。对于客户端和服务器，我将以单独的线程实现读和写。而且还没有实现适当的关闭套接字。在Oracle上可以找到一个更完整但更简单的示例。