网络编程的要素

IP和端口号

网络通信协议

TCP

客户端

1. 连接服务器socket
2. 发送消息

public static void main(String[] args) throws IOException {
    //创建一个socket连接
    Socket socket = new Socket(InetAddress.getByName("localhost"), 9000);
    //创建一个输出流
    OutputStream os = socket.getOutputStream();
    //读取文件
    FileInputStream fis = new FileInputStream(new File("old.png"));
    //写出文件
    byte [] buffer = new byte[1024];
    int len;
    while ((len = fis.read(buffer)) != -1) {
        os.write(buffer, 0, len);
    }
    //关闭资源
    fis.close();
    os.close();
    socket.close();
}

服务端

1. 建立服务的端口 ServerSocket
2. 等待用户的连接 accept
3. 接收用户的消息

public static void main(String[] args) throws IOException {
    //创建服务
    ServerSocket serverSocket = new ServerSocket(9000);
    //监听客户端的连接  阻塞式监听，会一直等待客户端连接
    Socket socket = serverSocket.accept();
    //获取输入流
    InputStream is = socket.getInputStream();

    //文件输出
    FileOutputStream fos = new FileOutputStream(new File("new.png"));
    byte[] buffer = new byte[1024];
    int len;
    while ((len = is.read(buffer)) != -1) {
        fos.write(buffer, 0, len);
    }

    //关闭资源
    fos.close();
    is.close();
    socket.close();
    serverSocket.close();
}

UDP

客户端

public static void main(String[] args) throws IOException{
    //建立一个socket
    DatagramSocket socket = new DatagramSocket();

    //创建一个需要发送的包
    String data = "Hello,server!";
    InetAddress localhost = InetAddress.getByName("localhost");
    int port = 9090;
    DatagramPacket packet = new DatagramPacket(data.getBytes(), 0, data.getBytes().length, localhost, port);

    //发送包
    socket.send(packet);
    //关闭流
    socket.close();
}

服务端

public static void main(String[] args) throws IOException {
    //开放端口
    DatagramSocket socket = new DatagramSocket(9090);
    //接收数据包
    byte[] buffer = new byte[1024];
    DatagramPacket packet = new DatagramPacket(buffer, 0, buffer.length);

    socket.receive(packet);  //阻塞接收
    System.out.println(new String(packet.getData(), 0, packet.getLength()));

    //关闭连接
    socket.close();
}

利用UDP编写简单的聊天通信

分别实现两个线程接口，一个一直发信息，一个一直接收信息。

发送线程

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

public class SendThread implements Runnable {
    private InetAddress ip;
    private int port;
    private String role;

    private DatagramSocket socket = null;
    private DatagramPacket packet = null;
    private BufferedReader reader = null;

    @Override
    public void run() {
        while (true) {
            try {
                String data = reader.readLine();
                byte[] datas = (this.role + "：" + data).getBytes();
                packet = new DatagramPacket(datas, 0, datas.length, this.ip, this.port);
                socket.send(packet);
                if (data.equals("bye")) {
                    break;
                }

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

    public SendThread (String ip, int port, String role) {
        //创建一个socket连接
        try {
            this.ip = InetAddress.getByName(ip);
            this.port = port;
            this.role = role;
            socket = new DatagramSocket();
            reader = new BufferedReader(new InputStreamReader(System.in));
        } catch (SocketException e) {
            e.printStackTrace();
        } catch (UnknownHostException e) {
            e.printStackTrace();
        }

    }
}

接收线程

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

public class ReceiveThread implements Runnable {
    private int port;

    private DatagramSocket socket = null;
    private DatagramPacket packet = null;

    @Override
    public void run() {
        while (true) {
            //准备接收包裹
            byte[] buffer = new byte[1024];
            packet = new DatagramPacket(buffer, 0, buffer.length);

            try {
                socket.receive(packet);  //阻塞接收
            } catch (IOException e) {
                e.printStackTrace();
            }
            String data = new String(packet.getData(), 0, packet.getLength());

            System.out.println(data);

            if (data.equals("bye")) {
                break;
            }
        }
        socket.close();
    }

    public ReceiveThread (int port) {
        this.port = port;

        try {
            socket = new DatagramSocket(port);
        } catch (SocketException e) {
            e.printStackTrace();
        }
    }
}

通信

//两个客户端分别创建两个线程，就可实现通信了

//老师端
new Thread(new SendThread("localhost", 9000, "老师")).start();
new Thread(new ReceiveThread(9090)).start();

//学生端
new Thread(new SendThread("localhost", 9090, "学生")).start();
new Thread(new ReceiveThread(9000)).start();

效果展示