面试题：Java Socket编程之多线程处理

Question

在Java Socket编程中，若有多个客户端连接到服务器，如何使用多线程来处理每个客户端的请求，以确保服务器能同时响应多个客户端？请简述实现思路并给出关键代码示例。

Answer 1

实现思路

1. 服务器端：
   • 创建一个 ServerSocket 实例，绑定到指定端口，监听客户端连接。
   • 当有客户端连接时，accept() 方法会返回一个 Socket 实例，代表与该客户端的连接。
   • 为每个客户端连接创建一个新的线程来处理其请求，这样服务器就能同时处理多个客户端。
2. 客户端：
   • 创建一个 Socket 实例，连接到服务器的指定地址和端口。
   • 通过该 Socket 实例的输入输出流与服务器进行数据交互。

关键代码示例

服务器端代码

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

public class Server {
    private static final int PORT = 12345;

    public static void main(String[] args) {
        try (ServerSocket serverSocket = new ServerSocket(PORT)) {
            System.out.println("Server started on port " + PORT);
            while (true) {
                Socket clientSocket = serverSocket.accept();
                System.out.println("Client connected: " + clientSocket);
                // 为每个客户端创建一个新线程来处理请求
                Thread clientHandler = new Thread(new ClientHandler(clientSocket));
                clientHandler.start();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private static class ClientHandler implements Runnable {
        private final Socket clientSocket;

        public ClientHandler(Socket clientSocket) {
            this.clientSocket = clientSocket;
        }

        @Override
        public void run() {
            try (
                BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
                PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true)
            ) {
                String inputLine;
                while ((inputLine = in.readLine()) != null) {
                    System.out.println("Received from client: " + inputLine);
                    out.println("Echo: " + inputLine);
                    if ("exit".equals(inputLine)) {
                        break;
                    }
                }
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                try {
                    clientSocket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

客户端代码

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 Client {
    private static final String SERVER_ADDRESS = "localhost";
    private static final int SERVER_PORT = 12345;

    public static void main(String[] args) {
        try (Socket socket = new Socket(SERVER_ADDRESS, SERVER_PORT);
             BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
             PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
             BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in))
        ) {
            String userInput;
            while ((userInput = stdIn.readLine()) != null) {
                out.println(userInput);
                System.out.println("Server response: " + in.readLine());
                if ("exit".equals(userInput)) {
                    break;
                }
            }
        } catch (UnknownHostException e) {
            System.err.println("Don't know about host: " + SERVER_ADDRESS);
            System.exit(1);
        } catch (IOException e) {
            System.err.println("Couldn't get I/O for the connection to: " + SERVER_ADDRESS);
            System.exit(1);
        }
    }
}