网络通信的三要素

IP地址
端口号
网络通信协议

TCP

客户端

import java.io.OutputStream;
import java.net.InetAddress;
import java.net.Socket;

public class TcpClient {
    public static void main(String[] args) throws Exception {
        // 创建要发生的ip地址
        InetAddress inetAddress = InetAddress.getByName("localhost");
        // 创建套接字
        Socket socket = new Socket(inetAddress, 9999);
        // 拿到输入流
        OutputStream outputStream = socket.getOutputStream();
        // 向输入流中放入要发送的信息并发送
        outputStream.write("你好".getBytes());
        // 关闭
        outputStream.close();
        socket.close();
    }
}

服务端

import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import java.net.ServerSocket;
import java.net.Socket;

public class TcpServer {

    public static void main(String[] args) throws Exception {
        // 创建服务器套接字，指定接收的端口
        ServerSocket serverSocket = new ServerSocket(9999);
        // 接收信息
        Socket socket = serverSocket.accept();
        // 下面是把信息存放到新的流中
        // 拿到输入流
        InputStream inputStream = socket.getInputStream();
        // 创建存放信息的数组输出流
        ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
        byte[] buffer = new byte[1024];
        int len;
        // 逐行读取信息放入buffer并放到输出流中
        while ((len = inputStream.read(buffer)) != -1)
            byteArrayOutputStream.write(buffer, 0, len);
        // 输出接收到的信息
        System.out.println(byteArrayOutputStream);
        // 关闭
        byteArrayOutputStream.close();
        inputStream.close();
        socket.close();
        serverSocket.close();
    }
}

先启动服务端，再启动客户端，之后可以看到服务端收到了客户端发的信息

UDP

发送端

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;

public class UdpSender {
    public static void main(String[] args) throws Exception {
        DatagramSocket datagramSocket = new DatagramSocket();
        InetAddress inetAddress = InetAddress.getByName("localhost");
        DatagramPacket datagramPacket = new DatagramPacket(
                "你好".getBytes(),           // 发送的数据
                0,                          // 数据长度从0开始 
                "你好".getBytes().length,    // 到末尾结束
                inetAddress,                // ip地址
                20000                       // 端口号
        );
        // 发送
        datagramSocket.send(datagramPacket);
        datagramSocket.close();
    }
}

接收端

import java.net.DatagramPacket;
import java.net.DatagramSocket;

public class UdpReceiver {
    public static void main(String[] args) throws Exception {
        DatagramSocket socket = new DatagramSocket(20000);
        byte[] buffer = new byte[1024];
        DatagramPacket packet = new DatagramPacket(buffer, 0 , buffer.length);
        socket.receive(packet);
        System.out.println(new String(packet.getData(), 0, packet.getLength()));
    }
}