java - 异步客户端 Java 套接字

Question

所以我正在实现一个简单的Java Socket Chat程序，但我遇到的问题是在下面的代码中。目前我的客户端代码将首先从套接字读取然后输出到屏幕，然后从控制台读取然后输出到套接字输入。但是这样，当它从控制台读取数据时，我无法从套接字打印消息，直到用户点击 enter 解决这个问题的最佳方法是什么，是多线程吗(如果是的话，我可以举个例子吗？)，或者是否有任何其他常规方法来处理这个问题。

        while(true){
            //read from socket, -> output to screen
            String line = sockin.readLine();
            System.out.println(line);

            //read console, -> write to socket
            String consolein = consoleReader.readLine();
            sockout.println(consolein);
        }

Answer 1

是的，您应该使用多线程。您需要生成两个线程，一个用于读取用户的输入，另一个用于读取服务器/另一个客户端的输出。但是，在基于控制台的聊天应用程序中使用多线程时，一个问题是:将服务器的输出与用户的输入分开。

示例多线程客户端

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.net.UnknownHostException;

public class ThreadedClient {

    public static void main(String[] args) {
        if (args.length != 2) {
            System.err.println(
                    "Usage: java ThreadedClient <host name> <port number>");
            System.exit(1);
        }

        String hostName = args[0];
        int portNumber = Integer.parseInt(args[1]);

        try {
            Socket serverSocket = new Socket(hostName, portNumber);
            ClientServerOutputReader csor = new ClientServerOutputReader(serverSocket);
            csor.start();
            ClientUserInputReader cuir = new ClientUserInputReader(serverSocket);
            cuir.start();
        } catch (UnknownHostException e) {
            System.err.println("Don't know about host " + hostName);
            System.exit(1);
        } catch (IOException e) {
            System.err.println("Couldn't get I/O for the connection to " +
                    hostName);
            System.exit(1);
        } 
    }

}

class ClientServerOutputReader extends Thread {
    Socket serverSocket;
    public ClientServerOutputReader(Socket serverSocket){
        this.serverSocket = serverSocket;
    }

    public void run() {
        try {
            BufferedReader in = new BufferedReader(
            new InputStreamReader(serverSocket.getInputStream()));

            String outputFromServer="";
            while((outputFromServer=in.readLine())!= null){
                //This part is printing the output to console
                //Instead it should be appending the output to some file
                //or some swing element. Because this output may overlap
                //the user input from console
                System.out.println(outputFromServer);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }

    }
}

class ClientUserInputReader extends Thread {
    Socket serverSocket;
    public ClientUserInputReader(Socket serverSocket){
        this.serverSocket = serverSocket;
    }
    public void run(){
        BufferedReader stdIn = new BufferedReader(
                 new InputStreamReader(System.in));
        PrintWriter out;
        try {
            out = new PrintWriter(serverSocket.getOutputStream(), true);
            String userInput;

            while ((userInput = stdIn.readLine()) != null) {
                out.println(userInput);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

运行:java ThreadedClient localhost 1982

示例回显服务器

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

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

        if (args.length != 1) {
            System.err.println("Usage: java EchoServer <port number>");
            System.exit(1);
        }

        int portNumber = Integer.parseInt(args[0]);

        try (
            ServerSocket serverSocket =
                new ServerSocket(Integer.parseInt(args[0]));
            Socket clientSocket = serverSocket.accept();     
            PrintWriter out =
                new PrintWriter(clientSocket.getOutputStream(), true);                   
            BufferedReader in = new BufferedReader(
                new InputStreamReader(clientSocket.getInputStream()));
        ) {
            String inputLine;
            while ((inputLine = in.readLine()) != null) {
                out.println("From Server:"+inputLine);
                Thread.sleep(2000);
                out.println("Server status on");
            }
        } catch (IOException e) {
            System.out.println("Exception caught when trying to listen on port "
                + portNumber + " or listening for a connection");
            System.out.println(e.getMessage());
        } catch (InterruptedException ie) {
             ie.printStackTrace();
        }
    }
}

在上面的服务器程序中，添加了手动 sleep 和自定义消息来模拟客户端发生用户输入时服务器的输出。

运行:java EchoServer 1982