使用java和套接字的簡單聊天程序

Question

我在Java中使用套接字時遇到問題：服務器沒有響應，也沒有拋出異常。

服務器代碼：

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Scanner;

class Server {
    public static void main(String args[]) {
        final int time = 75;
        //boolean CHAT_SESSION_ALIVE = false; 
        int port = 9999;

        try {
            System.out.println("Starting chat server using the port : " + port);
            ServerSocket srvr = new ServerSocket(port);
            Socket skt = srvr.accept();
            System.out.println("Server has connected with client         " + skt.getInetAddress());
            //CHAT_SESSION_ALIVE = true;

            PrintWriter out = new PrintWriter(skt.getOutputStream(), true);
            BufferedReader in = new BufferedReader(new InputStreamReader(skt.getInputStream()));

            new Thread(new Runnable() {
                @Override
                public void run() {
                    while (true) {
                        try {
                            if (in.ready()) {
                                String msg = in.readLine();
                                System.out.println("receive message: '" + msg + "'");
                                Thread.sleep(time);
                            }
                        } catch (Exception e) {
                            System.out.println(e);
                        }
                    }
                }
            }).start();

            new Thread(new Runnable() {
                @Override
                public void run() {
                    while (true) {
                        try {
                            Thread.sleep(time);
                            String msg = new Scanner(System.in).nextLine();
                            System.out.println("Sending message: '" + msg + "'");
                            out.print(msg);
                        } catch (Exception e) {
                            System.out.println(e);
                        }
                    }
                }
            }).start();

            //in.close();
            //out.close();
            //skt.close();
            //srvr.close();
        } catch (Exception e) {
            System.out.print(e);
        }
    }
}

客戶代碼：

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.util.Scanner;

class Client {
    public static void main(String args[]) {
        final int time = 75;
        //boolean CHAT_SESSION_ALIVE = false;
        int port = 9999;
        String hostIP = "127.0.0.1";

        try {
            Socket skt = new Socket(hostIP, port);
            System.out.println("Client has connected with server " + hostIP + ":" + port);
            //CHAT_SESSION_ALIVE = true;

            PrintWriter out = new PrintWriter(skt.getOutputStream(), true);
            BufferedReader in = new BufferedReader(new InputStreamReader(skt.getInputStream()));

            new Thread(new Runnable() {
                @Override
                public void run() {
                    while (true) {
                        try {
                            if (in.ready()) {
                                String msg = in.readLine();
                                System.out.println("receive message: '" + msg + "'");
                                Thread.sleep(time);
                            }
                        } catch (Exception e) {
                            System.out.println(e);
                        }
                    }
                }
            }).start();

            new Thread(new Runnable() {
                @Override
                public void run() {
                    while (true) {
                        try {
                            String msg = new Scanner(System.in).nextLine();
                            System.out.println("Sending message: '" + msg + "'");
                            out.print(msg);
                            Thread.sleep(time);
                        } catch (Exception e) {
                            System.out.println(e);
                        }
                    }
                }
            }).start();

            //in.close();
            //out.close();
            //skt.close();
        } catch (Exception e) {
            System.out.print(e);
        }
    }
}

服務器輸出：

使用端口啟動聊天服務器：9999
服務器已與客戶端/127.0.0.1連接

客戶輸出：

客戶端已與服務器127.0.0.1:9999連接
簡單的消息
發送消息：'簡單消息'

請解釋服務器無法正常工作的原因。

Answer 1

Scanner.nextLine返回沒有新行delim的行。 服務器正在使用BufferedReader.readLine ，它需要一個新行（如果沒有收到，則可能會阻塞）。 解決方案：在發送消息時附加分隔符。 如果使用print ，則必須明確刷新：

out.print(msg + "\n"); 
out.flush();//explicitly flush the stream

或者使用println方法讓它為你添加新行（並使用傳遞給PrintWriter構造函數的autoflush true標志）：

out.println(msg);//auto flushing 

Answer 2

在兩個代碼中，在PrintWriter out的實例化之后立即放置一個out.flush()