服务器没有向客户端发送回确认

Question

我在下面有我的服务器代码：

public void startServer() {
        ServerSocket listener = selectUnusedPortFromRange(1024, 65535);
        Thread t = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    String command = null;
                    while (true) {
                        Socket socket = listener.accept();
                        System.out.println("Got a connection from: " + socket.getLocalPort());
                        BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
                        command = in.readLine();
                        System.out.println("GOT HERE"); //Not being printed out
                        if (command != null && !"".equals(command)) {
                            if ("connection".equals(command)) {
                                Writer writer = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
                                writer.write("success\n");
                                writer.flush();
                            }
                        }
                    }
                }
            }
        }
        t.start();
}

这是我的客户端：

public void makeConnection() {
    try {
        Socket socket = new Socket(IP, PORT);
        Writer writer = new PrintWriter(socket.getOutputStream(), true);
        writer.write("connection\n");
        BufferedReader socketRead = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        String str;
        while ((str = socketRead.readLine()) != null) {
            if ("success".equals(str)) {
                System.out.println("Successfully saved all hosts to: " + listOfHosts.get(i));
                socketRead.close();
                socket.close();
                iStream.close();
                writer.close();
            }
        }
    }catch (Exception e) {
         System.out.println(e.getMessage());
    }
}

在客户端创建连接到服务器的套接字后，我将“连接”写入套接字的outputStream 并等待服务器返回确认成功。由于某种原因，没有与服务器建立连接。在服务器System.out.println("Got a connection from: " + socket.getLocalPort()); 中没有打印出这一行。

我做错了什么。我看不出来。当我尝试连接到我的服务器时，我没有抛出异常。

Answer 1

我面临着完全相同的问题。我通过使用 ACK 机制克服了它（不是我的想法，这是向我建议的）。这个想法是客户端将向服务器发出请求并保持套接字连接处于活动状态（并且输出流打开）直到服务器响应同意的 ACK 消息通过同一通道 .一旦客户端收到 ACK 消息，它才会关闭连接。

下面是服务器的代码：-

final ServerSocket listener = new ServerSocket(11111);
    Thread t = new Thread(new Runnable() {
        @Override
        public void run() {
            try {
                String command = null;
                 while (true) {
                    System.out.println("About to accept");
                    Socket socket = listener.accept();
                    System.out.println("Got a connection from: " + socket.getLocalPort());
                    DataInputStream inputStream = new DataInputStream(socket.getInputStream());
                    StringBuilder str = new StringBuilder(inputStream.readUTF());
                    //command = in.readLine();
                    System.out.println("GOT HERE. Msg received : "+str); 
                    if (str != null && !"".equals(str.toString())) {
                        command = str.toString();
                        if ("connection".equals(command)) {
                            System.out.println("Got connection message");
                             DataOutputStream outputStream = new DataOutputStream(socket.getOutputStream());
                            outputStream.writeUTF("connection");
                            outputStream.close();

                        }
                    }
                    inputStream.close();
                    System.out.println("Done");
                }
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
            }
        }
});
    t.start();

}

客户：-

public void makeConnection() {
    try {
        System.out.println("In makeConnection");
        Socket socket = new Socket("127.0.0.1", 11111);
        DataOutputStream outputStream = new DataOutputStream(socket.getOutputStream());
        outputStream.writeUTF("connection");
        InputStream inputStream = socket.getInputStream();
        DataInputStream dataInputStream = new DataInputStream(inputStream);
        StringBuilder str;
        do {
            str = new StringBuilder(dataInputStream.readUTF()); 
            } while (!str.toString().equals("connection"));
        System.out.println("Successfully saved all hosts to: ");
        outputStream.close();
        dataInputStream.close();
        socket.close();
        outputStream.close();
    }catch (Exception e) {
         System.out.println(e.getMessage());
    }
}

启动程序的调用：-

public void start() throws IOException, InterruptedException {
    System.out.println("Starting server");
    startServer();
    Thread.sleep(1000);
    System.out.println("Starting connection");
    makeConnection();
}

Answer 2

1) 确保客户端和服务器使用相同的端口。它们必须通过同一个端口进行通信。您目前可能正在使用不同的端口。

2) 确保您确实启动了您的服务器线程。在上面的代码中，您创建了一个新线程，但从不启动它。 t.start() 必须在某个地方调用。

3) 如果这是在您的本地计算机上，您最好使用localhost 而不是实际的 IP 地址。防火墙可能会以不同的方式处理您的外部 IP。

4) 使用换行符终止您的消息，例如\n，以便您的BufferedReader 可以使用它的readLine() 方法。为了更好地衡量，还可以通过刷新作者的缓冲区来跟进，以防换行符没有触发它。 writer.flush();

最后，确保在再次尝试运行代码之前终止 JVM。您的代码没有关闭机制来从端口取消绑定服务器......因此您可能会抛出异常，告诉您端口和/或地址已在使用中。如果发生这种情况，要么更改端口，要么终止在后台运行的 java 进程。

这是您的代码，稍作修改以在我的系统上运行。它正在按照您的预期工作。我试图尽可能少地改变，只是为了让它在我的系统上运行。需要注意的是，我将端口号硬编码到服务器和客户端中 - 这不是必需的，只是为了方便我进行测试：

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.Writer;
import java.net.ServerSocket;
import java.net.Socket;

public class Test {
    public static void main(String[] args) throws IOException {
        Test test = new Test();
        test.startServer();
        test.makeConnection();
    }

    public void startServer() throws IOException {
        final ServerSocket listener = new ServerSocket(60001);
        Thread t = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    String command = null;
                    while (true) {
                        Socket socket = listener.accept();
                        System.out.println("Got a connection from: " + socket.getLocalPort());
                        BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
                        command = in.readLine();
                        System.out.println("GOT HERE");
                        if (command != null && !"".equals(command)) {
                            if ("connection".equals(command)) {
                                Writer writer = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
                                writer.write("success\n");
                                writer.flush();
                            }
                        }
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
        t.start();
    }

    public void makeConnection() {
        System.out.println("Making Connection");;
        try {
            Socket socket = new Socket("localhost", 60001);
            Writer writer = new PrintWriter(socket.getOutputStream(), true);
            writer.write("connection\n");
            writer.flush();
            BufferedReader socketRead = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            String str;
            while ((str = socketRead.readLine()) != null) {
                if ("success".equals(str)) {
                    System.out.println("Successfully saved all hosts to: "); //+ listOfHosts.get(i));
                    socketRead.close();
                    socket.close();
                    //iStream.close();
                    writer.close();
                }
            }
        }catch (Exception e) {
             System.out.println(e.getMessage());
        }
    }

}