六、网络编程

1、windows系统的 端口检测 工具 tcping

下载地址 ：https://download.elifulkerson.com//files/tcping/0.39/tcping.exe (opens new window)

把 tcping.exe 工具放到目录 C:\Windows\System32下
打开控制台
使用方式 tcping ip 端口

这个工具类似于 linux系统上的 telnet工具 可以帮助我们在Windows系统上检测 远程端口的连通性

2、基于TCP协议的Socket(客户端)和ServerSocket(服务端)

Java的Socket是Java语言提供的一种用于网络通信的机制。它基于TCP/IP协议，允许应用程序通过网络进行数据交换。
Socket允许客户端和服务器之间建立连接，并在连接上进行数据传输。

Java中的Socket编程涉及两种基本类型：服务器Socket（ServerSocket）和客户端Socket（Socket）。
服务器Socket用于服务器端，监听客户端的连接请求并接受连接，而客户端Socket用于客户端，发起连接并与服务器通信。

简单的代码示例： 这个代码可以结合 上面的 NIO Selector 实现的群聊Demo 对比一下

使用 Java NIO提供的 ServerSocketChannel实现的服务端 仅使用单个线程就可以处理多个客户端连接

下面的ServerSocket 为了管理每个客户端连接 必须使用多线程为每个客户端连接都创建一个线程

服务端

import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;

public class ServerDemo {

    public static void main(String[] args) {
        //创建服务器Socket对象
        int port = 18848;
        try (ServerSocket ss = new ServerSocket(port)) {
            while (true) {
                //监听客户端连接，返回一个对应的Socket对象
                Socket s = ss.accept();
                //为每一个客户端开启一个线程
                new Thread(() -> {
                    try (InputStream inputStream = s.getInputStream();
                         OutputStream outputStream = s.getOutputStream();
                         BufferedWriter bwServer = new BufferedWriter(new OutputStreamWriter(outputStream));) {
                        //接收数据写到文本文件
                        BufferedReader br = new BufferedReader(new InputStreamReader(inputStream));
                        String str = br.readLine();
                        while (str != null) {
                            // 打印客户端输入的内容
                            System.out.println(str);
                            //给出反馈
                            bwServer.write("Accept Successfully!");
                            bwServer.newLine();
                            bwServer.flush();
                            str = br.readLine();
                        }

                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }).start();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

客户端A

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

public class ClientA {

    public static void main(String[] args){
        //创建客户端Socket对象
        try (Socket s = new Socket("127.0.0.1", 18848);
             BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(s.getOutputStream()));
             BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
             BufferedReader sbr = new BufferedReader(new InputStreamReader(s.getInputStream()));){

            String line;
            while ((line = br.readLine()) != null) {
                bw.write("客户端A："+line);
                bw.newLine();
                bw.flush();

                // 新增：读取并打印服务器反馈
                String serverResponse = sbr.readLine();
                if (serverResponse != null) {
                    System.out.println("服务器反馈：" + serverResponse);
                }
            }

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

客户端B

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.Socket;

public class ClientB {

    public static void main(String[] args){
        //创建客户端Socket对象
        try (Socket s = new Socket("127.0.0.1", 18848);
             BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(s.getOutputStream()));
             BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
             BufferedReader sbr = new BufferedReader(new InputStreamReader(s.getInputStream()));){

            String line;
            while ((line = br.readLine()) != null) {
                bw.write("客户端B："+line);
                bw.newLine();
                bw.flush();

                // 新增：读取并打印服务器反馈
                String serverResponse = sbr.readLine();
                if (serverResponse != null) {
                    System.out.println("服务器反馈：" + serverResponse);
                }
            }

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

演示效果如下：

3、 基于UDP协议的DatagramSocket

简单代码示例：
服务端：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;

public class AAA {

    public static void main(String[] args) {
        int port = 18848;
        try (DatagramSocket serverSocket = new DatagramSocket(port);) {
            byte[] buffer = new byte[1024];
            DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
            byte[] sendBuffer;

            while (true) {
                // 接收数据
                serverSocket.receive(packet);
                String message = new String(packet.getData(), 0, packet.getLength());
                System.out.println(message);

                // 准备回复消息并发送
                String replyMessage = "收到消息: " + message;
                sendBuffer = replyMessage.getBytes();
                InetAddress clientAddress = packet.getAddress();
                int clientPort = packet.getPort();
                DatagramPacket sendPacket = new DatagramPacket(sendBuffer, sendBuffer.length, clientAddress, clientPort);
                serverSocket.send(sendPacket);
            }

        } catch (Exception e) {
            e.printStackTrace();
        }

    }
}

客户端

class ClientAAA {

    public static void main(String[] args) throws IOException {
        String hostname = "localhost";
        int port = 18848;

        try (DatagramSocket clientSocket = new DatagramSocket();
             BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));) {
            InetAddress address = InetAddress.getByName(hostname);

            String s = "";
            while ((s = bufferedReader.readLine()) != null) {
                byte[] buffer = s.getBytes();
                DatagramPacket packet = new DatagramPacket(buffer, buffer.length, address, port);
                clientSocket.send(packet);

                // 接收服务器的回复
                byte[] receiveBuffer = new byte[1024];
                DatagramPacket receivePacket = new DatagramPacket(receiveBuffer, receiveBuffer.length);
                clientSocket.receive(receivePacket);
                String serverReply = new String(receivePacket.getData(), 0, receivePacket.getLength());
                System.out.println(serverReply);
            }

        } catch (Exception e) {
            e.printStackTrace();
        }

    }

}

运行结果：