在Java中，使用Socket結合多線程可以實現客戶端和服務器之間的多線程通信。下面是一個簡單的示例，展示了如何使用Java Socket實現多線程通信。

服務器端代碼：

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

public class Server {
    public static void main(String[] args) throws IOException, InterruptedException {
        int port = 12345;
        ExecutorService executorService = Executors.newFixedThreadPool(10); // 創建一個固定大小的線程池

        ServerSocket serverSocket = new ServerSocket(port);
        System.out.println("Server is listening on port " + port);

        while (true) {
            Socket clientSocket = serverSocket.accept();
            executorService.execute(new ClientHandler(clientSocket)); // 將客戶端連接交給線程池處理
        }
    }
}

class ClientHandler implements Runnable {
    private Socket clientSocket;

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

    @Override
    public void run() {
        try {
            InputStream inputStream = clientSocket.getInputStream();
            BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));

            String message;
            while ((message = reader.readLine()) != null) {
                System.out.println("Received from client: " + message);

                // 發送響應給客戶端
                OutputStream outputStream = clientSocket.getOutputStream();
                PrintWriter writer = new PrintWriter(outputStream, true);
                writer.println("Server response: " + message);
            }

            clientSocket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

客戶端代碼：

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

public class Client {
    public static void main(String[] args) throws IOException {
        String serverAddress = "localhost";
        int port = 12345;

        Socket socket = new Socket(serverAddress, port);
        System.out.println("Connected to server");

        BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        PrintWriter writer = new PrintWriter(socket.getOutputStream(), true);

        // 發送消息給服務器
        writer.println("Hello, Server!");
        System.out.println("Sent message to server");

        // 讀取服務器的響應
        String response = reader.readLine();
        System.out.println("Received from server: " + response);

        socket.close();
    }
}

在這個示例中，服務器使用了一個固定大小的線程池來處理客戶端連接。當服務器接收到一個新的客戶端連接時，它會將這個連接交給線程池中的一個線程來處理。這樣可以確保服務器能夠同時處理多個客戶端連接，而不會因為處理單個連接而阻塞其他連接。

客戶端通過Socket連接到服務器，并發送一條消息給服務器。服務器接收到消息后，會將其原樣返回給客戶端。客戶端在接收到服務器的響應后，關閉與服務器的連接。