Java基础（14）UDP、TCP

UDP（用户数据报协议）和TCP（传输控制协议）是互联网协议套件（TCP/IP）的两个核心协议，用于数据的传输。这两个协议在功能上是相互补充的，分别适用于不同的网络应用场景。

TCP（传输控制协议）

TCP是一种面向连接的、可靠的、基于字节流的传输层通信协议。它能确保数据包的顺序传输和数据的完整性，适用于对数据准确性要求高的应用，如Web浏览、文件传输、电子邮件等。

TCP的特点：

面向连接：通信双方在数据传送前，必须先建立连接。
数据传输可靠性：通过序号、确认应答、重传控制等机制保证数据的正确传输。
拥塞控制和流量控制：通过滑动窗口机制等控制数据的流量，避免网络拥塞。

TCP示例代码（Java）

服务器端示例：

import java.io.*;
import java.net.*;public class TCPServer {public static void main(String[] args) throws IOException {int port = 6789;ServerSocket welcomeSocket = new ServerSocket(port);while (true) {Socket connectionSocket = welcomeSocket.accept();BufferedReader inFromClient =new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());String clientSentence = inFromClient.readLine();System.out.println("Received: " + clientSentence);String capitalizedSentence = clientSentence.toUpperCase() + '\n';outToClient.writeBytes(capitalizedSentence);}}
}

客户端示例：

import java.io.*;
import java.net.*;public class TCPClient {public static void main(String[] args) throws IOException {String sentence;String modifiedSentence;BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in));Socket clientSocket = new Socket("hostname", 6789);DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));sentence = inFromUser.readLine();outToServer.writeBytes(sentence + '\n');modifiedSentence = inFromServer.readLine();System.out.println("FROM SERVER: " + modifiedSentence);clientSocket.close();}
}

UDP（用户数据报协议）

UDP是一种无连接的协议。与TCP不同，它不保证数据包的顺序或完整性，因此，它更适用于对实时性要求高的应用，如视频会议、在线游戏等。

UDP的特点：

无连接：发送数据之前不需要建立连接，减少了开销和发送数据之前的延迟。
效率高，结构简单：适用于广播和多播传输。
不保证可靠传输：不进行错误校验和修正，适用于对实时性要求较高的场景。

UDP示例代码（Java）

服务器端示例：

import java.io.*;
import java.net.*;public class UDPServer {public static void main(String[] args) throws IOException {DatagramSocket serverSocket = new DatagramSocket(9876);byte[] receiveData = new byte[1024];byte[] sendData = new byte[1024];while (true) {DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);serverSocket.receive(receivePacket);String sentence = new String(receivePacket.getData(), 0, receivePacket.getLength());System.out.println("RECEIVED: " + sentence);InetAddress IPAddress = receivePacket.getAddress();int port = receivePacket.getPort();String capitalizedSentence = sentence.toUpperCase();sendData = capitalizedSentence.getBytes();DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddress, port);serverSocket.send(sendPacket);}}
}

客户端示例：

import java.io.*;
import java.net.*;public class UDPClient {public static void main(String[] args) throws IOException {BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in));DatagramSocket clientSocket = new DatagramSocket();InetAddress IPAddress = InetAddress.getByName("hostname");byte[] sendData = new byte[1024];byte[] receiveData = new byte[1024];String sentence = inFromUser.readLine();sendData = sentence.getBytes();DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddress, 9876);clientSocket.send(sendPacket);DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);clientSocket.receive(receivePacket);String modifiedSentence = new String(receivePacket.getData(), 0, receivePacket.getLength());System.out.println("FROM SERVER:" + modifiedSentence);clientSocket.close();}
}