第五知识单元

import java.net.InetAddress;
public class IPHostConvertSample {
    public static void main(String args[]) {
        try {
            InetAddress ia = InetAddress.getByName("www.ncut.edu.cn");
            String ip = ia.getHostAddress(); // IP address
            String hostname = ia.getHostName(); // Hostname
            System.out.println("IP address: " + ip);
            System.out.println("Hostname: " + hostname);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

// Server.java
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;
public class Server {
    public static void main(String[] args) {
        try {
            int number = 0;
            // 指定服务器监听的端口号，需和客户端中一致
            ServerSocket serverSocket = new ServerSocket(3456);
            System.out.println("Running...");
            while(true) {
                // 服务器监听客户端连接，阻塞方法
                Socket socket = serverSocket.accept();
                InputStream is = socket.getInputStream(); // 服务器接收数据
                byte b[] = new byte[1024];
                int len = is.read(b);
                System.out.print("(Length: " + len + ") ");
                String s = new String(b, 0, len);
                System.out.println("Message from client: " + s);
                OutputStream os = socket.getOutputStream(); // 服务器发送数据
                String sendStr = "Hi there #" + number++;
                os.write(sendStr.getBytes());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

// Client.java
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.Socket;
import java.net.UnknownHostException;
public class Client {
    public static void main(String[] args) {
        try {
            // 创建一个套接字对象，第一个参数填写服务器的ip地址，第二个参数填写服务器的端口号
            Socket socket = new Socket("localhost", 3456);
            OutputStream os = socket.getOutputStream(); // 向服务器发送数据
            String inputStr = "Hi";
            if (args.length == 1) { inputStr = args[0]; }
            os.write(inputStr.getBytes());
            InputStream is = socket.getInputStream(); // 从服务器接收数据
            byte b[] = new byte[1024];
            int len = is.read(b);
            String s = new String(b, 0, len);
            System.out.println("Message from server: " + s);
            is.close(); // 关闭输入流
            os.close(); // 关闭输出流
            socket.close(); // 关闭套接字
        } catch (UnknownHostException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}