在Java中實現網絡通信，通常需要使用到Java套接字編程（Socket Programming）。套接字是一種用于實現不同計算機間或同一計算機內的進程間通信的技術。以下是一個簡單的Java網絡通信示例，展示了如何使用TCP協議進行客戶端和服務器之間的通信：

1. 服務器端代碼（Server.java）：

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

public class Server {
    public static void main(String[] args) throws IOException {
        int port = 12345;
        ServerSocket serverSocket = new ServerSocket(port);
        System.out.println("Server is listening on port " + port);

        Socket socket = serverSocket.accept();
        System.out.println("Client connected");

        InputStream inputStream = socket.getInputStream();
        BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));

        OutputStream outputStream = socket.getOutputStream();
        PrintWriter writer = new PrintWriter(outputStream, true);

        String line;
        while ((line = reader.readLine()) != null) {
            System.out.println("Received: " + line);
            writer.println("Server received: " + line);
        }

        socket.close();
        serverSocket.close();
    }
}

2. 客戶端代碼（Client.java）：

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");

        OutputStream outputStream = socket.getOutputStream();
        PrintWriter writer = new PrintWriter(outputStream, true);

        InputStream inputStream = socket.getInputStream();
        BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));

        BufferedReader console = new BufferedReader(new InputStreamReader(System.in));
        String line;

        while (true) {
            System.out.print("Enter a message: ");
            line = console.readLine();
            if (line == null || line.equalsIgnoreCase("exit")) {
                break;
            }

            writer.println(line);
            System.out.println("Sent: " + line);

            String response = reader.readLine();
            System.out.println("Server response: " + response);
        }

        socket.close();
    }
}

首先運行服務器端代碼（Server.java），然后運行客戶端代碼（Client.java）。客戶端將連接到服務器并發送消息，服務器將接收消息并將其原樣返回。當客戶端輸入"exit"時，連接將關閉。