TCP三次握手/TCP三次挥手

“三次握手”的目的是“为了防止已失效的连接请求报文段突然又传送到了服务端，因而产生 错误”。主要目的防止 server 端一直等待，浪费资源。换句话说，即是为了保证服务端能收 接受到客户端的信息并能做出正确的应答而进行前两次(第一次和第二次)握手，为了保证客 户端能够接收到服务端的信息并能做出正确的应答而进行后两次(第二次和第三次)握手。

“四次挥手”原因是因为 tcp 是全双工模式，接收到 FIN 时意味将没有数据再发来，但是还是 可以继续发送数据。

TCP三次握手

TCP四次挥手

完整报文

# 三次握手:SYN=1 Seq=0
No.     Time           Source                Destination           Protocol Length Info50 7.055660280    127.0.0.1             127.0.0.1             TCP      74     44156 → 12345 [SYN] Seq=0 Win=65495 Len=0 MSS=65495 SACK_PERM TSval=2731439096 TSecr=0 WS=128Frame 50: 74 bytes on wire (592 bits), 74 bytes captured (592 bits) on interface lo, id 0Section number: 1Interface id: 0 (lo)Encapsulation type: Ethernet (1)Arrival Time: Aug 29, 2023 08:26:32.312489778 EDT[Time shift for this packet: 0.000000000 seconds]Epoch Time: 1693311992.312489778 seconds[Time delta from previous captured frame: 0.004110298 seconds][Time delta from previous displayed frame: 0.000000000 seconds][Time since reference or first frame: 7.055660280 seconds]Frame Number: 50Frame Length: 74 bytes (592 bits)Capture Length: 74 bytes (592 bits)[Frame is marked: False][Frame is ignored: False][Protocols in frame: eth:ethertype:ip:tcp][Coloring Rule Name: TCP SYN/FIN][Coloring Rule String: tcp.flags & 0x02 || tcp.flags.fin == 1]
Ethernet II, Src: 00:00:00_00:00:00 (00:00:00:00:00:00), Dst: 00:00:00_00:00:00 (00:00:00:00:00:00)
Internet Protocol Version 4, Src: 127.0.0.1, Dst: 127.0.0.1
Transmission Control Protocol, Src Port: 44156, Dst Port: 12345, Seq: 0, Len: 0# 三次握手:SYN1 ACK=1 Seq=0
No.     Time           Source                Destination           Protocol Length Info51 7.055692471    127.0.0.1             127.0.0.1             TCP      74     12345 → 44156 [SYN, ACK] Seq=0 Ack=1 Win=65483 Len=0 MSS=65495 SACK_PERM TSval=2731439096 TSecr=2731439096 WS=128Frame 51: 74 bytes on wire (592 bits), 74 bytes captured (592 bits) on interface lo, id 0Section number: 1Interface id: 0 (lo)Encapsulation type: Ethernet (1)Arrival Time: Aug 29, 2023 08:26:32.312521969 EDT[Time shift for this packet: 0.000000000 seconds]Epoch Time: 1693311992.312521969 seconds[Time delta from previous captured frame: 0.000032191 seconds][Time delta from previous displayed frame: 0.000032191 seconds][Time since reference or first frame: 7.055692471 seconds]Frame Number: 51Frame Length: 74 bytes (592 bits)Capture Length: 74 bytes (592 bits)[Frame is marked: False][Frame is ignored: False][Protocols in frame: eth:ethertype:ip:tcp][Coloring Rule Name: TCP SYN/FIN][Coloring Rule String: tcp.flags & 0x02 || tcp.flags.fin == 1]
Ethernet II, Src: 00:00:00_00:00:00 (00:00:00:00:00:00), Dst: 00:00:00_00:00:00 (00:00:00:00:00:00)
Internet Protocol Version 4, Src: 127.0.0.1, Dst: 127.0.0.1
Transmission Control Protocol, Src Port: 12345, Dst Port: 44156, Seq: 0, Ack: 1, Len: 0# 三次握手:Ack=1 Seq=1
No.     Time           Source                Destination           Protocol Length Info52 7.055725041    127.0.0.1             127.0.0.1             TCP      66     44156 → 12345 [ACK] Seq=1 Ack=1 Win=65536 Len=0 TSval=2731439096 TSecr=2731439096Frame 52: 66 bytes on wire (528 bits), 66 bytes captured (528 bits) on interface lo, id 0Section number: 1Interface id: 0 (lo)Encapsulation type: Ethernet (1)Arrival Time: Aug 29, 2023 08:26:32.312554539 EDT[Time shift for this packet: 0.000000000 seconds]Epoch Time: 1693311992.312554539 seconds[Time delta from previous captured frame: 0.000032570 seconds][Time delta from previous displayed frame: 0.000032570 seconds][Time since reference or first frame: 7.055725041 seconds]Frame Number: 52Frame Length: 66 bytes (528 bits)Capture Length: 66 bytes (528 bits)[Frame is marked: False][Frame is ignored: False][Protocols in frame: eth:ethertype:ip:tcp][Coloring Rule Name: TCP][Coloring Rule String: tcp]
Ethernet II, Src: 00:00:00_00:00:00 (00:00:00:00:00:00), Dst: 00:00:00_00:00:00 (00:00:00:00:00:00)
Internet Protocol Version 4, Src: 127.0.0.1, Dst: 127.0.0.1
Transmission Control Protocol, Src Port: 44156, Dst Port: 12345, Seq: 1, Ack: 1, Len: 0# 客户端发送消息  Hello, server!.
No.     Time           Source                Destination           Protocol Length Info53 7.057834891    127.0.0.1             127.0.0.1             TCP      81     44156 → 12345 [PSH, ACK] Seq=1 Ack=1 Win=65536 Len=15 TSval=2731439098 TSecr=2731439096Frame 53: 81 bytes on wire (648 bits), 81 bytes captured (648 bits) on interface lo, id 0Section number: 1Interface id: 0 (lo)Encapsulation type: Ethernet (1)Arrival Time: Aug 29, 2023 08:26:32.314664389 EDT[Time shift for this packet: 0.000000000 seconds]Epoch Time: 1693311992.314664389 seconds[Time delta from previous captured frame: 0.002109850 seconds][Time delta from previous displayed frame: 0.002109850 seconds][Time since reference or first frame: 7.057834891 seconds]Frame Number: 53Frame Length: 81 bytes (648 bits)Capture Length: 81 bytes (648 bits)[Frame is marked: False][Frame is ignored: False][Protocols in frame: eth:ethertype:ip:tcp:data][Coloring Rule Name: TCP][Coloring Rule String: tcp]
Ethernet II, Src: 00:00:00_00:00:00 (00:00:00:00:00:00), Dst: 00:00:00_00:00:00 (00:00:00:00:00:00)
Internet Protocol Version 4, Src: 127.0.0.1, Dst: 127.0.0.1
Transmission Control Protocol, Src Port: 44156, Dst Port: 12345, Seq: 1, Ack: 1, Len: 15
Data (15 bytes)0000  48 65 6c 6c 6f 2c 20 73 65 72 76 65 72 21 0a      Hello, server!.# 服务端应答
No.     Time           Source                Destination           Protocol Length Info54 7.057859991    127.0.0.1             127.0.0.1             TCP      66     12345 → 44156 [ACK] Seq=1 Ack=16 Win=65536 Len=0 TSval=2731439098 TSecr=2731439098Frame 54: 66 bytes on wire (528 bits), 66 bytes captured (528 bits) on interface lo, id 0Section number: 1Interface id: 0 (lo)Encapsulation type: Ethernet (1)Arrival Time: Aug 29, 2023 08:26:32.314689489 EDT[Time shift for this packet: 0.000000000 seconds]Epoch Time: 1693311992.314689489 seconds[Time delta from previous captured frame: 0.000025100 seconds][Time delta from previous displayed frame: 0.000025100 seconds][Time since reference or first frame: 7.057859991 seconds]Frame Number: 54Frame Length: 66 bytes (528 bits)Capture Length: 66 bytes (528 bits)[Frame is marked: False][Frame is ignored: False][Protocols in frame: eth:ethertype:ip:tcp][Coloring Rule Name: TCP][Coloring Rule String: tcp]
Ethernet II, Src: 00:00:00_00:00:00 (00:00:00:00:00:00), Dst: 00:00:00_00:00:00 (00:00:00:00:00:00)
Internet Protocol Version 4, Src: 127.0.0.1, Dst: 127.0.0.1
Transmission Control Protocol, Src Port: 12345, Dst Port: 44156, Seq: 1, Ack: 16, Len: 0#  服务端发送消息 Server received: Hello, server!.
No.     Time           Source                Destination           Protocol Length Info55 7.059237157    127.0.0.1             127.0.0.1             TCP      98     12345 → 44156 [PSH, ACK] Seq=1 Ack=16 Win=65536 Len=32 TSval=2731439100 TSecr=2731439098Frame 55: 98 bytes on wire (784 bits), 98 bytes captured (784 bits) on interface lo, id 0Section number: 1Interface id: 0 (lo)Encapsulation type: Ethernet (1)Arrival Time: Aug 29, 2023 08:26:32.316066655 EDT[Time shift for this packet: 0.000000000 seconds]Epoch Time: 1693311992.316066655 seconds[Time delta from previous captured frame: 0.001377166 seconds][Time delta from previous displayed frame: 0.001377166 seconds][Time since reference or first frame: 7.059237157 seconds]Frame Number: 55Frame Length: 98 bytes (784 bits)Capture Length: 98 bytes (784 bits)[Frame is marked: False][Frame is ignored: False][Protocols in frame: eth:ethertype:ip:tcp:data][Coloring Rule Name: TCP][Coloring Rule String: tcp]
Ethernet II, Src: 00:00:00_00:00:00 (00:00:00:00:00:00), Dst: 00:00:00_00:00:00 (00:00:00:00:00:00)
Internet Protocol Version 4, Src: 127.0.0.1, Dst: 127.0.0.1
Transmission Control Protocol, Src Port: 12345, Dst Port: 44156, Seq: 1, Ack: 16, Len: 32
Data (32 bytes)0000  53 65 72 76 65 72 20 72 65 63 65 69 76 65 64 3a   Server received:
0010  20 48 65 6c 6c 6f 2c 20 73 65 72 76 65 72 21 0a    Hello, server!.# 客户端还给了一个回应
No.     Time           Source                Destination           Protocol Length Info56 7.059273656    127.0.0.1             127.0.0.1             TCP      66     44156 → 12345 [ACK] Seq=16 Ack=33 Win=65536 Len=0 TSval=2731439100 TSecr=2731439100Frame 56: 66 bytes on wire (528 bits), 66 bytes captured (528 bits) on interface lo, id 0Section number: 1Interface id: 0 (lo)Encapsulation type: Ethernet (1)Arrival Time: Aug 29, 2023 08:26:32.316103154 EDT[Time shift for this packet: 0.000000000 seconds]Epoch Time: 1693311992.316103154 seconds[Time delta from previous captured frame: 0.000036499 seconds][Time delta from previous displayed frame: 0.000036499 seconds][Time since reference or first frame: 7.059273656 seconds]Frame Number: 56Frame Length: 66 bytes (528 bits)Capture Length: 66 bytes (528 bits)[Frame is marked: False][Frame is ignored: False][Protocols in frame: eth:ethertype:ip:tcp][Coloring Rule Name: TCP][Coloring Rule String: tcp]
Ethernet II, Src: 00:00:00_00:00:00 (00:00:00:00:00:00), Dst: 00:00:00_00:00:00 (00:00:00:00:00:00)
Internet Protocol Version 4, Src: 127.0.0.1, Dst: 127.0.0.1
Transmission Control Protocol, Src Port: 44156, Dst Port: 12345, Seq: 16, Ack: 33, Len: 0# 四次挥手 1 FIN=1 Ack=33 Seq=16
No.     Time           Source                Destination           Protocol Length Info57 7.062253079    127.0.0.1             127.0.0.1             TCP      66     44156 → 12345 [FIN, ACK] Seq=16 Ack=33 Win=65536 Len=0 TSval=2731439103 TSecr=2731439100Frame 57: 66 bytes on wire (528 bits), 66 bytes captured (528 bits) on interface lo, id 0Section number: 1Interface id: 0 (lo)Encapsulation type: Ethernet (1)Arrival Time: Aug 29, 2023 08:26:32.319082577 EDT[Time shift for this packet: 0.000000000 seconds]Epoch Time: 1693311992.319082577 seconds[Time delta from previous captured frame: 0.002979423 seconds][Time delta from previous displayed frame: 0.002979423 seconds][Time since reference or first frame: 7.062253079 seconds]Frame Number: 57Frame Length: 66 bytes (528 bits)Capture Length: 66 bytes (528 bits)[Frame is marked: False][Frame is ignored: False][Protocols in frame: eth:ethertype:ip:tcp][Coloring Rule Name: TCP SYN/FIN][Coloring Rule String: tcp.flags & 0x02 || tcp.flags.fin == 1]
Ethernet II, Src: 00:00:00_00:00:00 (00:00:00:00:00:00), Dst: 00:00:00_00:00:00 (00:00:00:00:00:00)
Internet Protocol Version 4, Src: 127.0.0.1, Dst: 127.0.0.1
Transmission Control Protocol, Src Port: 44156, Dst Port: 12345, Seq: 16, Ack: 33, Len: 0# 四次挥手 2 ACK=17 Seq=33
No.     Time           Source                Destination           Protocol Length Info58 7.110165407    127.0.0.1             127.0.0.1             TCP      66     12345 → 44156 [ACK] Seq=33 Ack=17 Win=65536 Len=0 TSval=2731439151 TSecr=2731439103Frame 58: 66 bytes on wire (528 bits), 66 bytes captured (528 bits) on interface lo, id 0Section number: 1Interface id: 0 (lo)Encapsulation type: Ethernet (1)Arrival Time: Aug 29, 2023 08:26:32.366994905 EDT[Time shift for this packet: 0.000000000 seconds]Epoch Time: 1693311992.366994905 seconds[Time delta from previous captured frame: 0.047912328 seconds][Time delta from previous displayed frame: 0.047912328 seconds][Time since reference or first frame: 7.110165407 seconds]Frame Number: 58Frame Length: 66 bytes (528 bits)Capture Length: 66 bytes (528 bits)[Frame is marked: False][Frame is ignored: False][Protocols in frame: eth:ethertype:ip:tcp][Coloring Rule Name: TCP][Coloring Rule String: tcp]
Ethernet II, Src: 00:00:00_00:00:00 (00:00:00:00:00:00), Dst: 00:00:00_00:00:00 (00:00:00:00:00:00)
Internet Protocol Version 4, Src: 127.0.0.1, Dst: 127.0.0.1
Transmission Control Protocol, Src Port: 12345, Dst Port: 44156, Seq: 33, Ack: 17, Len: 0# 四次挥手: 3 Fin=1 Ack=17 Seq=33
No.     Time           Source                Destination           Protocol Length Info61 7.390471256    127.0.0.1             127.0.0.1             TCP      66     12345 → 44156 [FIN, ACK] Seq=33 Ack=17 Win=65536 Len=0 TSval=2731439431 TSecr=2731439103Frame 61: 66 bytes on wire (528 bits), 66 bytes captured (528 bits) on interface lo, id 0Section number: 1Interface id: 0 (lo)Encapsulation type: Ethernet (1)Arrival Time: Aug 29, 2023 08:26:32.647300754 EDT[Time shift for this packet: 0.000000000 seconds]Epoch Time: 1693311992.647300754 seconds[Time delta from previous captured frame: 0.000234452 seconds][Time delta from previous displayed frame: 0.280305849 seconds][Time since reference or first frame: 7.390471256 seconds]Frame Number: 61Frame Length: 66 bytes (528 bits)Capture Length: 66 bytes (528 bits)[Frame is marked: False][Frame is ignored: False][Protocols in frame: eth:ethertype:ip:tcp][Coloring Rule Name: TCP SYN/FIN][Coloring Rule String: tcp.flags & 0x02 || tcp.flags.fin == 1]
Ethernet II, Src: 00:00:00_00:00:00 (00:00:00:00:00:00), Dst: 00:00:00_00:00:00 (00:00:00:00:00:00)
Internet Protocol Version 4, Src: 127.0.0.1, Dst: 127.0.0.1
Transmission Control Protocol, Src Port: 12345, Dst Port: 44156, Seq: 33, Ack: 17, Len: 0# 四次挥手 4 Ack=34 Seq=17
No.     Time           Source                Destination           Protocol Length Info62 7.390499061    127.0.0.1             127.0.0.1             TCP      66     44156 → 12345 [ACK] Seq=17 Ack=34 Win=65536 Len=0 TSval=2731439431 TSecr=2731439431Frame 62: 66 bytes on wire (528 bits), 66 bytes captured (528 bits) on interface lo, id 0Section number: 1Interface id: 0 (lo)Encapsulation type: Ethernet (1)Arrival Time: Aug 29, 2023 08:26:32.647328559 EDT[Time shift for this packet: 0.000000000 seconds]Epoch Time: 1693311992.647328559 seconds[Time delta from previous captured frame: 0.000027805 seconds][Time delta from previous displayed frame: 0.000027805 seconds][Time since reference or first frame: 7.390499061 seconds]Frame Number: 62Frame Length: 66 bytes (528 bits)Capture Length: 66 bytes (528 bits)[Frame is marked: False][Frame is ignored: False][Protocols in frame: eth:ethertype:ip:tcp][Coloring Rule Name: TCP][Coloring Rule String: tcp]
Ethernet II, Src: 00:00:00_00:00:00 (00:00:00:00:00:00), Dst: 00:00:00_00:00:00 (00:00:00:00:00:00)
Internet Protocol Version 4, Src: 127.0.0.1, Dst: 127.0.0.1
Transmission Control Protocol, Src Port: 44156, Dst Port: 12345, Seq: 17, Ack: 34, Len: 0

实例代码

HttpSampleClient

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;public class HttpSampleClient {public static void main(String[] args) {try {URL url = new URL("http://localhost:8080");HttpURLConnection connection = (HttpURLConnection) url.openConnection();connection.setRequestMethod("GET");int responseCode = connection.getResponseCode();System.out.println("Response Code:" + responseCode);// read contentBufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));String line;StringBuilder response = new StringBuilder();while ((line = reader.readLine()) != null) {response.append(line);}reader.close();System.out.println("Response Body: " + response);connection.disconnect();} catch (Exception e) {e.printStackTrace();}}
}

HttpSampleServer

import com.sun.net.httpserver.HttpExchange;
import com.sun.net.httpserver.HttpHandler;
import com.sun.net.httpserver.HttpServer;import java.io.IOException;
import java.io.OutputStream;
import java.net.InetSocketAddress;public class HttpSampleServer {public static void main(String[] args) {try {// create http server to bind 8080HttpServer server = HttpServer.create(new InetSocketAddress("127.0.0.1", 8080), 0);// bind pathserver.createContext("/", new MyHandler());server.start();System.out.println("Http Sever started on port 8080");} catch (Exception e) {e.printStackTrace();}}static class MyHandler implements HttpHandler {// 设置响应头c@Overridepublic void handle(HttpExchange exchange) throws IOException {String response = "Hello from the local HTTP server!";exchange.sendResponseHeaders(200, response.getBytes().length);// 获取输出流并写入响应内容OutputStream os = exchange.getResponseBody();os.write(response.getBytes());os.close();}}
}

HttpsSampleClient

import javax.net.ssl.*;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;public class HttpsSampleClient {public static void main(String[] args) {try {// Create and configure the SSL contextSSLContext sslContext = SSLContext.getInstance("TLS");sslContext.init(null, new TrustManager[]{new X509TrustManager() {public java.security.cert.X509Certificate[] getAcceptedIssuers() {return null;}public void checkClientTrusted(java.security.cert.X509Certificate[] certs, String authType) {}public void checkServerTrusted(java.security.cert.X509Certificate[] certs, String authType) {}}}, new java.security.SecureRandom());// Create an SSL socketSSLSocketFactory sslSocketFactory = sslContext.getSocketFactory();SSLSocket socket = (SSLSocket) sslSocketFactory.createSocket("localhost", 12345);// Get input and output streams for secure communicationBufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));PrintWriter writer = new PrintWriter(socket.getOutputStream(), true); // autoFlush// Send a message to the serverString message = "Hello, server!";writer.println(message);// Read response from the serverString serverResponse = reader.readLine();System.out.println("Server response: " + serverResponse);// Close resourcesreader.close();writer.close();socket.close();} catch (Exception e) {e.printStackTrace();}}
}

HttpsSampleServer

import javax.net.ssl.*;
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.security.KeyStore;public class HttpsSampleServer {public static void main(String[] args) {String keystorePath = "./keystore.jks";char[] keystorePassword = "flannery".toCharArray();try {// Load the keystore containing the server's SSL certificateKeyStore keystore = KeyStore.getInstance("JKS");keystore.load(new FileInputStream(keystorePath), keystorePassword);// Create and configure the SSL contextKeyManagerFactory kmf = KeyManagerFactory.getInstance("SunX509");kmf.init(keystore, keystorePassword);SSLContext sslContext = SSLContext.getInstance("TLS");sslContext.init(kmf.getKeyManagers(), null, null);// Create an SSL server socketSSLServerSocketFactory sslServerSocketFactory = sslContext.getServerSocketFactory();SSLServerSocket serverSocket = (SSLServerSocket) sslServerSocketFactory.createServerSocket(12345);System.out.println("Server listening on port 12345...");// Wait for a client to connectSSLSocket clientSocket = (SSLSocket) serverSocket.accept();System.out.println("Client connected: " + clientSocket.getInetAddress().getHostAddress());// Get input and output streams for secure communicationBufferedReader reader = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));PrintWriter writer = new PrintWriter(clientSocket.getOutputStream(), true); // autoFlush// Read data from client and respondString clientMessage;while ((clientMessage = reader.readLine()) != null) {System.out.println("Received from client: " + clientMessage);writer.println("Server received: " + clientMessage);}// Close resourcesreader.close();writer.close();clientSocket.close();serverSocket.close();} catch (Exception e) {e.printStackTrace();}}
}

TcpSampleClient

import java.io.*;
import java.net.Socket;public class TcpSampleClient {public static void main(String[] args) {try {// Create a socket to connect to the serverSocket socket = new Socket("localhost", 12345);// Get input and output streams for the socketInputStream inputStream = socket.getInputStream();OutputStream outputStream = socket.getOutputStream();// Create readers and writers for easier communicationBufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));PrintWriter writer = new PrintWriter(outputStream, true); // autoFlush// Send a message to the serverString message = "Hello, server!";writer.println(message);// Read response from the serverString serverResponse = reader.readLine();System.out.println("Server response: " + serverResponse);// Close resourcesreader.close();writer.close();socket.close();} catch (IOException e) {e.printStackTrace();}}
}

TcpSampleServer

import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;
public class TcpSampleServer {public static void main(String[] args) {extracted();}private static void extracted() {try {// Create a server socketServerSocket serverSocket = new ServerSocket(12345);System.out.println("Server listening on port 12345...");// Wait for a client to connectSocket clientSocket = serverSocket.accept();System.out.println("Client connected: " + clientSocket.getInetAddress().getHostAddress());// Get input and output streams for the socketInputStream inputStream = clientSocket.getInputStream();OutputStream outputStream = clientSocket.getOutputStream();// Create readers and writers for easier communicationBufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));PrintWriter writer = new PrintWriter(outputStream, true); // autoFlush// Read data from client and respondString clientMessage;while ((clientMessage = reader.readLine()) != null) {System.out.println("Received from client: " + clientMessage);writer.println("Server received: " + clientMessage);}// Close resources//reader.close();//writer.close();//clientSocket.close();//serverSocket.close();} catch (IOException e) {e.printStackTrace();}}}

UdpSampleClient

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;public class UdpSampleClient {public static void main(String[] args) {try {DatagramSocket clientSocket = new DatagramSocket();String message = "Hello, server!";byte[] sendData = message.getBytes();InetAddress serverAddress = InetAddress.getByName("localhost");int serverPort = 12345;DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, serverAddress, serverPort);clientSocket.send(sendPacket);byte[] receiveData = new byte[1024];DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);clientSocket.receive(receivePacket);String serverResponse = new String(receivePacket.getData(), 0, receivePacket.getLength());System.out.println("Server response: " + serverResponse);clientSocket.close();} catch (IOException e) {e.printStackTrace();}}}

UdpSampleSever

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;public class UdpSampleSever {public static void main(String[] args) {try {DatagramSocket serverSocket = new DatagramSocket(12345);System.out.println("Server listening on port 12345...");byte[] receiveData = new byte[1024];while (true) {DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);serverSocket.receive(receivePacket);String clientMessage = new String(receivePacket.getData(), 0, receivePacket.getLength());System.out.println("Received from client: " + clientMessage);InetAddress clientAddress = receivePacket.getAddress();int clientPort = receivePacket.getPort();String serverResponse = "Server received: " + clientMessage;byte[] sendData = serverResponse.getBytes();DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, clientAddress, clientPort);serverSocket.send(sendPacket);}} catch (IOException e) {e.printStackTrace();}}
}

资料

超详细的wireshark抓包使用教程
jks证书文件的生成步骤
如何使用wireshark抓取HTTPS数据包？
wireshark抓包分析HTTPS
Burp Suite的基本介绍及使用
渗透测试工具Burp Suite详解
vmware ctrl键粘滞的问题
wireshark过滤规则
Burp Suite HTTPS详解