Java 'SyncServer' 允许两个用户同时编辑一个字符串变量

Question

我很难找到问题的原因。

程序的功能如下... Server 允许多个用户登录(连接到服务器)并编辑名为 text 的同一个字符串变量rep:(用于替换整个字符串)或 app:(附加到字符串)的起始命令。

当客户端连接时，他们必须输入命令。无论命令是什么，它都会在同一个窗口中回显给他们(在不同的 CMD 窗口中同时运行服务器和客户端)。因此，如果他们输入 hello，回显将是 ECHO: hello。

如果输入的命令是rep:tight，则服务器中的text 字符串变量应更改为包含tight，然后应返回back/在客户端 cmd 窗口中显示为 tight - 没有 ECHO。

如果之后的命令是app:rope，则服务器中的text 字符串变量应更改为包含tightrope 并应返回back/在客户端 cmd 窗口中显示为 tightrope。

此外，用户不能输入 4 个字符以下的任何值，因此 SynchClient 应显示错误消息并提示用户输入另一个值。

我遇到的问题是我的回显值在每次新输入后都没有改变。我得到了第一个输入命令的返回，仅此而已，我正在努力解决这一切。

编辑:如果您自己运行程序可能是最好的。

这是我的 SynchServer.java 文件的样子:

import java.io.*;
import java.net.*;
import java.util.*;

public class SynchServer
{

    public static void main(String[] args) throws IOException
    {
        ServerSocket serverSocket = null;
        final int PORT = 1234;
        Socket client;
        ClientHandler handler;

        try
        {
            serverSocket = new ServerSocket(PORT);
        }
        catch (IOException ioEx)
        {
            System.out.println("\nUnable to set up port!");
            System.exit(1);
        }

        System.out.println("\nServer running...\n");

        do
        {
            //Wait for client.
            client = serverSocket.accept();

            System.out.println("\nNew client accepted.\n");
            handler = new ClientHandler(client);
            handler.start();
        }while (true);
    }
}

class ClientHandler extends Thread
{
    private Socket client;
    private Scanner input;
    private PrintWriter output;

    private static String text = "";

    public ClientHandler(Socket socket) throws IOException
    {
        client = socket;

        input = new Scanner(client.getInputStream());
        output = new PrintWriter(client.getOutputStream(),true);
    }

    public void run()
    {
        String head, tail, received;

        received = input.nextLine();
        head = received.substring(0, 4);
        tail = received.substring(4);

        while (!received.equals("QUIT"))
        {
            if (head.equals("rep:"))
                changeText(tail);

            else
                if (head.equals("app:"))
                    appendText(tail);

            output.println(text);
            output.println("ECHO: " + received);
        }

        try
        {
            System.out.println("Closing down connection...");
            client.close();
        }
        catch(IOException ioEx)
        {
            System.out.println("* Disconnection problem! *");
        }
    }

    private synchronized void changeText(String changedText)
    {
        text = changedText;
    }

    private synchronized void appendText(String appendedText)
    {
        text += appendedText;
    }
}

和我的 SynchClient.java 文件:

import java.io.*;
import java.net.*;
import java.util.*;

public class SynchClient
{

    public static void main(String[] args) throws IOException
    {
        InetAddress host = null;
        final int PORT = 1234;
        Socket socket;
        Scanner networkInput,keyboard;
        PrintWriter output;

        try
        {
            host = InetAddress.getLocalHost();
        }
        catch(UnknownHostException uhEx)
        {
            System.out.println("\nHost ID not found!\n");
        }

        socket = new Socket(host, PORT);
        networkInput = new Scanner(socket.getInputStream());
        output = new PrintWriter(socket.getOutputStream(),true);

        keyboard = new Scanner(System.in);

        String message, response;

        do
        {   
            System.out.print("\nEnter message ('QUIT' to exit): ");
            message = keyboard.nextLine();

            if (message.length() < 4)
            {
                System.out.print("\nPlease enter a value greater than 4 characters: ");
                message = keyboard.nextLine();
            }

            output.println(message);

            if (!message.equals("QUIT"))
                {
                    response = networkInput.nextLine();
                    System.out.println("\n" + response);
                }
        }while (!message.equals("QUIT"));

        try
        {
            System.out.println("\nClosing down connection...\n");
            socket.close();
        }
        catch(IOException ioEx)
        {
            System.out.println("\n* Disconnection problem! *\n");
        }
    }
}

编辑 2:我的工作解决方案:

服务器:

public class SynchServer
{

    public static void main(String[] args) throws IOException
    {
        ServerSocket serverSocket = null;
        final int PORT = 1234;
        Socket client;
        ClientHandler handler;

        try
        {
            serverSocket = new ServerSocket(PORT);
        }
        catch (IOException ioEx)
        {
            System.out.println("\nUnable to set up port!");
            System.exit(1);
        }

        System.out.println("\nServer running...\n");

        do
        {
            //Wait for client.
            client = serverSocket.accept();

            System.out.println("\nNew client accepted.\n");
            handler = new ClientHandler(client);
            handler.start();
        }while (true);
    }
}

class ClientHandler extends Thread
{
    private Socket client;
    private Scanner input;
    private PrintWriter output;

    private static String text = "";

    public ClientHandler(Socket socket) throws IOException
    {
        client = socket;

        input = new Scanner(client.getInputStream());
        output = new PrintWriter(client.getOutputStream(),true);
    }

    public void run()
    {
        String head, tail, received;

        received = input.nextLine();

        // create head and tail in case first input is rep: or app:
        head = received.substring(0, 4);
        tail = received.substring(4);

        while (!received.equals("QUIT"))
        {
            if (head.equals("rep:"))
            {
                changeText(tail);
                output.println(text);
                // input for next one
            }
            else
                if (head.equals("app:"))
                {
                    appendText(tail);
                    output.println(text);
                    // get input for next
                }
            else
            {
                //must be some random thing that just needs to be echoed
                output.println(text);
            }

            //Get next input
            received = input.nextLine();
            //and set the head and tail again
            head = received.substring(0, 4);
            tail = received.substring(4);
        }

        try
        {
            System.out.println("Closing down connection...");
            client.close();
        }
        catch(IOException ioEx)
        {
            System.out.println("* Disconnection problem! *");
        }
    }

    private synchronized void changeText(String changedText)
    {
        text = changedText;
    }

    private synchronized void appendText(String appendedText)
    {
        text += appendedText;
    }
}

客户:

public class SynchClient
{

    public static void main(String[] args) throws IOException
    {
        InetAddress host = null;
        final int PORT = 1234;
        Socket socket;
        Scanner networkInput,keyboard;
        PrintWriter output;

        try
        {
            host = InetAddress.getLocalHost();
        }
        catch(UnknownHostException uhEx)
        {
            System.out.println("\nHost ID not found!\n");
        }

        socket = new Socket(host, PORT);
        networkInput = new Scanner(socket.getInputStream());
        output = new PrintWriter(socket.getOutputStream(),true);

        keyboard = new Scanner(System.in);

        String message, response;

        do
        {
            System.out.print("\nEnter message ('QUIT' to exit): ");
            message = keyboard.nextLine();

            while (message.length() < 4)
            {
                System.out.print("\nPlease enter 4 or more characters: ");
                message = keyboard.nextLine();
            }

            output.println(message);
            if (!message.equals("QUIT"))
            {
                response = networkInput.nextLine();

                System.out.println("\n" + response);
            }

        }while (!message.equals("QUIT"));

        try
        {
            System.out.println("\nClosing down connection...\n");
            socket.close();
        }
        catch(IOException ioEx)
        {
            System.out.println("\n* Disconnection problem! *\n");
        }
    }
}

Answer 1

这根本不是关于 static 字段的。你的错误在这个循环中:

       while (!received.equals("QUIT")) {
            if (head.equals("rep:"))
                changeText(tail);

            else if (head.equals("app:"))
                appendText(tail);

            output.println(text);
            output.println("ECHO: " + received);
        }

它会在第一次客户端输入后无限运行，并且不会每次都从输入流中读取新值。

这些行:

        received = input.nextLine();
        head = received.substring(0, 4);
        tail = received.substring(4);

应该放入循环中:

    while (!received.equals("QUIT")) {
        received = input.nextLine();
        head = received.substring(0, 4);
        tail = received.substring(4);
        ...

更新:

准确地说，它还有另一个次要问题，这两行:

            output.println(text);
            output.println("ECHO: " + received);

它们应该变成:

        output.println("ECHO: " + text);

(否则您将发送不需要的两条单独的行)。