另一个客户端由于其防火墙而无法连接到客户端A。
您可以创建两种主要的网络：
服务器客户端
点对点
但是客户端可以将一些数据保存到服务器，服务器可以将它们发送给所有客户端（您不需要点对点网络就可以让客户端B向客户端A发送一些数据）。
示例：客户端B将其地图位置发送到服务器，服务器将数据发送给所有客户端，因此客户端A能够在客户端B的位置绘制字符图块。
要将两台PC连接在一起，您需要将端口从服务器的调制解调器转发到用作服务器的PC，然后从用作服务器的PC的防火墙打开该端口。
您还可以在这里看看如何使用python创建一个多人游戏，我举了一个示例，其中客户端可以将它们与IRC连接在一起，并可以玩井字游戏（因此您不必管理服务器）
）。我在这篇文章的结尾添加了一个Java示例。
一个简单的服务器示例：
import java.io.BufferedReader;import java.io.BufferedWriter;import java.io.InputStreamReader;import java.io.OutputStreamWriter;import java.net.ServerSocket;import java.net.Socket;import java.util.Date;public class Server{ public static void main(String[] args) throws Exception { ServerSocket listener = new ServerSocket(4000); String line; try { while (true) { Socket socket = listener.accept(); BufferedReader readerChannel = new BufferedReader(new InputStreamReader(socket.getInputStream())); BufferedWriter writerChannel = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())); try { writerChannel.write(new Date().toString() + "nr"); writerChannel.flush(); while ((line = readerChannel.readLine()) != null) { System.out.println(line); } } finally { socket.close(); } } } finally { listener.close(); } }}一个简单的客户端示例：
import java.io.BufferedReader;import java.io.BufferedWriter;import java.io.InputStreamReader;import java.io.OutputStreamWriter;import java.net.Socket;import java.util.Date;public class Client{ public static void main(String[] args) throws Exception { Socket socket = new Socket("127.0.0.1", 4000); BufferedWriter writerChannel = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())); BufferedReader readerChannel = new BufferedReader(new InputStreamReader(socket.getInputStream())); String line; writerChannel.write(new Date().toString() + "nr"); writerChannel.flush(); while ((line = readerChannel.readLine()) != null) { System.out.println(line); } }}还可以看看：
import javax.net.ssl.SSLSocket;import javax.net.ssl.SSLSocketFactory;public class Client{ public static void main(String[] args) throws Exception { SSLSocketFactory socketBuilder = (SSLSocketFactory) SSLSocketFactory.getDefault(); SSLSocket socket = (SSLSocket) socketBuilder.createSocket("127.0.0.1", 4000); }}一个简单的IRC示例：
import java.io.BufferedReader;import java.io.BufferedWriter;import java.io.InputStreamReader;import java.io.OutputStreamWriter;import javax.net.ssl.SSLSocket;import javax.net.ssl.SSLSocketFactory;public class Client{ public static void main(String[] args) throws Exception { SSLSocketFactory socketBuilder = (SSLSocketFactory) SSLSocketFactory.getDefault(); SSLSocket socket = (SSLSocket) socketBuilder.createSocket("irc.freenode.net", 6697); BufferedWriter writerChannel = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())); BufferedReader readerChannel = new BufferedReader(new InputStreamReader(socket.getInputStream())); String line, computerName, nick, login, channel = "#bot", channelPassword = ""; long id = 1; computerName = java.net.InetAddress.getLocalHost().getHostName(); nick = computerName + "_" + id; login = computerName + "_" + id; writerChannel.write("NICK " + nick + "rn"); // Join IRC with a specific Nick writerChannel.write("USER " + login + " 8 * :" + login + " rn"); // Join IRC with a specific User writerChannel.flush(); while ((line = readerChannel.readLine()) != null) { if (line.indexOf("004") != -1) // If connected { break; } else if (line.indexOf("433") != -1) // If Nick already in use { id++; nick = computerName + "_" + id; login = computerName + "_" + id; writerChannel.write("NICK " + nick + "rn"); writerChannel.write("USER " + login + " 8 * :" + login + " rn"); writerChannel.flush(); } } writerChannel.write("JOIN " + channel + " " + channelPassword + "rn"); // Join a channel writerChannel.flush(); while ((line = readerChannel.readLine()) != null) { try { line = line.substring(line.indexOf("#")); channel = line.substring(0, line.indexOf(" ")); if (line.toLowerCase().startsWith("ping")) // avoid ping time-out { writerChannel.write("PONG :" + line.substring(5) + "rn"); writerChannel.flush(); } else if (line.toLowerCase().contains("!ping")) { writerChannel.write("PRIVMSG " + channel + " :pongrn"); writerChannel.flush(); } else if (line.toLowerCase().contains("!join")) { String newChannel = line.substring(line.indexOf("!join") + 6); int stringPosition; if ((stringPosition = newChannel.indexOf(" ")) != -1) { String newPassword = newChannel.substring(stringPosition + 1); newChannel = newChannel.substring(0, stringPosition); writerChannel.write("JOIN " + newChannel + " " + newPassword + "rn"); writerChannel.flush(); } else { writerChannel.write("JOIN " + newChannel + "rn"); writerChannel.flush(); } } else if (line.toLowerCase().contains("!leave")) { writerChannel.write("PART " + channel + "rn"); writerChannel.flush(); } else if (line.toLowerCase().contains("!quit")) { writerChannel.write("QUITrn"); writerChannel.flush(); System.exit(0); } } catch (Exception e) { } } }}我无法为您提供对等网络的示例，因为我从未这样做过。这确实很困难，您必须在互联网上进行大量研究。
更多信息：
https://docs.oracle.com/javase/7/docs/api/java/net/Socket.html
https://docs.oracle.com/javase/tutorial/networking/sockets/
http://www.oracle.com/technetwork/java/socket-140484.html
您需要一个多线程服务器来处理许多不同的连接。
提示-我已经回答了一些类似的问题。 即使编程语言有时有所不同，我也会为您提供链接，但逻辑总是相同的，因此可以为您提供帮助：
在python中创建多人游戏
Xpre Mass Multiplayer（不是您可能在想的）
MMO如何处理真人游戏的每一刻为成千上万的玩家计算和发送数据包？
