java - 为什么这个基本的客户端-服务器程序不传递数据？

Question

我正在关注网络方面的 Java Trail。当我将用作示例的三个 KnockKnock 类(客户端、服务器和协议(protocol))复制/粘贴到 Eclipse 中时，它们按预期工作。然而，我真正想做的是消除协议(protocol)类，让服务器回显给客户端，无论我在控制台中输入什么内容。我尝试主要通过注释掉对协议(protocol)类的引用来修改服务器程序，但不知何故，我最终破坏了程序。

我太新了，我不知道哪里出了问题，而且我在电子书和网站上搜索答案越多，我就越困惑。我发现我对 IO 流的真正工作原理几乎一无所知。我按顺序粘贴了以下所有三个类:服务器、客户端、协议(protocol)。问题出在哪里以及为什么会出现问题:

服务器:

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

public class KnockKnockServer {
    public static void main(String[] args) throws IOException {

        ServerSocket serverSocket = null;
        try {
            serverSocket = new ServerSocket(4444);
        } catch (IOException e) {
            System.err.println("Could not listen on port: 4444.");
            System.exit(1);
        }

        Socket clientSocket = null;
        try {
            clientSocket = serverSocket.accept();
            System.out.println("Client Accepted");
        } catch (IOException e) {
            System.err.println("Accept failed.");
            System.exit(1);
        }

        PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
        BufferedReader in = new BufferedReader(
                new InputStreamReader(
                clientSocket.getInputStream()));
        String inputLine, outputLine;
        //KnockKnockProtocol kkp = new KnockKnockProtocol();

        //outputLine = kkp.processInput(null);
        //out.println(outputLine);

        while ((inputLine = in.readLine()) != null) {
             //outputLine = kkp.processInput(inputLine);
             //out.println(outputLine);
            out.println(inputLine);
             if (inputLine.equals("Bye."))
                break;
        }
        out.close();
        in.close();
        clientSocket.close();
        serverSocket.close();
    }
}

客户:

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

public class KnockKnockClient {
    public static void main(String[] args) throws IOException {

        Socket kkSocket = null;
        PrintWriter out = null;
        BufferedReader in = null;

        try {
            kkSocket = new Socket("localhost", 4444);
            out = new PrintWriter(kkSocket.getOutputStream(), true);
            in = new BufferedReader(new InputStreamReader(kkSocket.getInputStream()));
        } catch (UnknownHostException e) {
            System.err.println("Don't know about host: taranis.");
            System.exit(1);
        } catch (IOException e) {
            System.err.println("Couldn't get I/O for the connection to: taranis.");
            System.exit(1);
        }

        BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
        String fromServer;
        String fromUser;

        while ((fromServer = in.readLine()) != null) {
            System.out.println("Server: " + fromServer);
            if (fromServer.equals("Bye."))
                break;

            fromUser = stdIn.readLine();
        if (fromUser != null) {
                System.out.println("Client: " + fromUser);
                out.println(fromUser);
        }
        }

        out.close();
        in.close();
        stdIn.close();
        kkSocket.close();
    }
}

协议(protocol):

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

public class KnockKnockProtocol {
    private static final int WAITING = 0;
    private static final int SENTKNOCKKNOCK = 1;
    private static final int SENTCLUE = 2;
    private static final int ANOTHER = 3;

    private static final int NUMJOKES = 5;

    private int state = WAITING;
    private int currentJoke = 0;

    private String[] clues = { "Turnip", "Little Old Lady", "Atch", "Who", "Who" };
    private String[] answers = { "Turnip the heat, it's cold in here!",
                                 "I didn't know you could yodel!",
                                 "Bless you!",
                                 "Is there an owl in here?",
                                 "Is there an echo in here?" };

    public String processInput(String theInput) {
        String theOutput = null;

        if (state == WAITING) {
            theOutput = "Knock! Knock!";
            state = SENTKNOCKKNOCK;
        } else if (state == SENTKNOCKKNOCK) {
            if (theInput.equalsIgnoreCase("Who's there?")) {
                theOutput = clues[currentJoke];
                state = SENTCLUE;
            } else {
                theOutput = "You're supposed to say \"Who's there?\"! " +
                "Try again. Knock! Knock!";
            }
        } else if (state == SENTCLUE) {
            if (theInput.equalsIgnoreCase(clues[currentJoke] + " who?")) {
                theOutput = answers[currentJoke] + " Want another? (y/n)";
                state = ANOTHER;
            } else {
                theOutput = "You're supposed to say \"" + 
                clues[currentJoke] + 
                " who?\"" + 
                "! Try again. Knock! Knock!";
                state = SENTKNOCKKNOCK;
            }
        } else if (state == ANOTHER) {
            if (theInput.equalsIgnoreCase("y")) {
                theOutput = "Knock! Knock!";
                if (currentJoke == (NUMJOKES - 1))
                    currentJoke = 0;
                else
                    currentJoke++;
                state = SENTKNOCKKNOCK;
            } else {
                theOutput = "Bye.";
                state = WAITING;
            }
        }
        return theOutput;
    }
}

Answer 1

我认为你的问题只是两个应用程序都在等待:当KKServer启动时，它会等待客户端，然后等待客户端“说”一些话，客户端等待服务器说一些话，然后再等待用户输入