1
// 获取本机IP
2
InetAddress localHost = InetAddress.getLocalHost();
3
System.out.println("本机: " + localHost);
4

5
// 获取域名对应的IP
6
InetAddress baidu = InetAddress.getByName("www.baidu.com");
7
System.out.println("百度IP: " + baidu.getHostAddress());
8

9
// 检查可达性（会发ICMP包）
10
boolean reachable = baidu.isReachable(5000);

1
public class TCPServer {
2
    public static void main(String[] args) throws IOException {
3
        ServerSocket serverSocket = new ServerSocket(8080);
4
        System.out.println("服务端启动，监听8080端口...");
5

6
        while (true) {
7
            // accept() 是阻塞的，直到有客户端连接
8
            Socket socket = serverSocket.accept();
9
            // 每个客户端开一个线程处理
10
            new Thread(() -> handleClient(socket)).start();
11
        }
12
    }
13

14
    private static void handleClient(Socket socket) {
15
        try (BufferedReader in = new BufferedReader(
16
                new InputStreamReader(socket.getInputStream()));
17
             PrintWriter out = new PrintWriter(
18
                socket.getOutputStream(), true)) {
19

20
            String message;
21
            while ((message = in.readLine()) != null) {
22
                System.out.println("收到: " + message);
23
                out.println("服务端回复: " + message);
24
                if ("bye".equals(message)) break;
25
            }
26
        } catch (IOException e) {
27
            e.printStackTrace();
28
        }
29
    }
30
}

1
public class TCPClient {
2
    public static void main(String[] args) throws IOException {
3
        try (Socket socket = new Socket("localhost", 8080);
4
             BufferedReader in = new BufferedReader(
5
                new InputStreamReader(socket.getInputStream()));
6
             PrintWriter out = new PrintWriter(
7
                socket.getOutputStream(), true);
8
             BufferedReader keyboard = new BufferedReader(
9
                new InputStreamReader(System.in))) {
10

11
            System.out.println("已连接到服务器");
12
            String message;
13
            while ((message = keyboard.readLine()) != null) {
14
                out.println(message);
15
                String response = in.readLine();
16
                System.out.println("服务端回复: " + response);
17
                if ("bye".equals(message)) break;
18
            }
19
        }
20
    }
21
}

1
public class UDPServer {
2
    public static void main(String[] args) throws Exception {
3
        DatagramSocket socket = new DatagramSocket(8080);
4
        byte[] buffer = new byte[1024];
5

6
        while (true) {
7
            DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
8
            socket.receive(packet); // 阻塞等待
9

10
            String message = new String(packet.getData(), 0, packet.getLength());
11
            System.out.println("收到: " + message + " 来自: " + packet.getAddress());
12

13
            // 回复
14
            String response = "服务端收到: " + message;
15
            byte[] responseData = response.getBytes();
16
            DatagramPacket responsePacket = new DatagramPacket(
17
                responseData, responseData.length,
18
                packet.getAddress(), packet.getPort());
19
            socket.send(responsePacket);
20
        }
21
    }
22
}

1
public class UDPClient {
2
    public static void main(String[] args) throws Exception {
3
        DatagramSocket socket = new DatagramSocket();
4
        InetAddress serverAddr = InetAddress.getByName("localhost");
5

6
        BufferedReader keyboard = new BufferedReader(
7
            new InputStreamReader(System.in));
8

9
        String message;
10
        while ((message = keyboard.readLine()) != null) {
11
            // 发送
12
            byte[] data = message.getBytes();
13
            DatagramPacket packet = new DatagramPacket(
14
                data, data.length, serverAddr, 8080);
15
            socket.send(packet);
16

17
            // 接收回复
18
            byte[] buffer = new byte[1024];
19
            DatagramPacket responsePacket = new DatagramPacket(buffer, buffer.length);
20
            socket.receive(responsePacket);
21
            String response = new String(responsePacket.getData(), 0, responsePacket.getLength());
22
            System.out.println("服务端回复: " + response);
23

24
            if ("bye".equals(message)) break;
25
        }
26
        socket.close();
27
    }
28
}

1
URL url = new URL("https://api.github.com/users/octocat");
2
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
3
conn.setRequestMethod("GET");
4
conn.setRequestProperty("Accept", "application/json");
5

6
int responseCode = conn.getResponseCode();
7
System.out.println("响应码: " + responseCode);
8

9
BufferedReader in = new BufferedReader(
10
    new InputStreamReader(conn.getInputStream()));
11
String line;
12
StringBuilder content = new StringBuilder();
13
while ((line = in.readLine()) != null) {
14
    content.append(line);
15
}
16
in.close();
17
conn.disconnect();
18

19
System.out.println("响应内容: " + content);

1
HttpClient client = HttpClient.newHttpClient();
2

3
HttpRequest request = HttpRequest.newBuilder()
4
    .uri(URI.create("https://api.github.com/users/octocat"))
5
    .header("Accept", "application/json")
6
    .build();
7

8
HttpResponse<String> response = client.send(
9
    request, HttpResponse.BodyHandlers.ofString());
10

11
System.out.println("响应码: " + response.statusCode());
12
System.out.println("响应内容: " + response.body());