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一.传输层:

1.UDP:无连接,不可靠,面向数据报,全双工.

2.TCP:有连接,可靠,面向字节流,全双工.

注意:这里的可不可靠是相对的,并且和安不安全无关.

二.UDP数据报套接字编程:

1.socket文件:表示网卡的这类文件.

 2.DatagramPacket:表示一个UDP数据报.

 

三.代码实现:

1.回显服务器代码:

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;
import java.nio.charset.StandardCharsets;public class EchoUDPServer {// 服务器private DatagramSocket socket = null;public EchoUDPServer(int port) throws SocketException {// 服务器端指定端口号socket = new DatagramSocket(port);}public void start() throws IOException {System.out.println("启动服务器");// 由于服务器不会停止工作,所以使用死循环while (true) {// 1.读取请求,并解析// 类似于数组的输出型参数,不过要手动输入数组类型和大小DatagramPacket requestPacket = new DatagramPacket(new byte[4096], 4096);socket.receive(requestPacket);// 客户端的数据是一个文本字符串String request = new String(requestPacket.getData(), 0, requestPacket.getLength());// 2.根据请求,计算机相应String response = this.process(request);// 3.把相应写会给客户端// 注意第二个参数的长度DatagramPacket responsePacket = new DatagramPacket(response.getBytes(), response.getBytes().length,requestPacket.getSocketAddress());socket.send(responsePacket);System.out.println(responsePacket.getSocketAddress() + "  接受内容:" + request + "  回复内容:" + response);}}public String process(String request) {return request;}public static void main(String[] args) throws IOException {// 服务器端口号由自己指定(1025~65535),0~1024最好不要使用EchoUDPServer server = new EchoUDPServer(1999);//EchoUDPServer server = new DictionaryUDPServer(1999);server.start();}
}

 

2.回显客户端代码:

import java.io.IOException;
import java.net.*;
import java.nio.charset.StandardCharsets;
import java.util.Scanner;public class EchoUDPClient {// 客户端private DatagramSocket socket = null;private String serverIp = null;private int serverPort;public EchoUDPClient(String serverIp, int serverPort) throws SocketException {socket = new DatagramSocket();this.serverIp = serverIp;this.serverPort = serverPort;}public void start() throws IOException {Scanner scanner = new Scanner(System.in);System.out.println("客户端启动");while (true) {System.out.println("->");// 1.从控制台获取用户输入String request = scanner.nextLine();// 2.构造请求对象,发送给服务器DatagramPacket requestPacket = new DatagramPacket(request.getBytes(), 0, request.getBytes().length,InetAddress.getByName(serverIp), serverPort);socket.send(requestPacket);// 3.读取服务器响应,解析响应内容DatagramPacket responsePacket = new DatagramPacket(new byte[4096], 4096);socket.receive(responsePacket);String response = new String(responsePacket.getData(), 0, responsePacket.getLength());// 4.显示在屏幕上System.out.println(response);}}public static void main(String[] args) throws IOException {EchoUDPClient client = new EchoUDPClient("127.0.0.1", 1999);client.start();}
}

3.字典服务器代码: 

 

import java.io.IOException;
import java.net.SocketException;
import java.util.HashMap;
import java.util.Map;public class DictionaryUDPServer extends EchoUDPServer{private Map<String, String> dictionary = new HashMap<>();public DictionaryUDPServer(int port) throws SocketException {super(port);dictionary.put("I", "我");dictionary.put("love", "爱");dictionary.put("China", "中国");}@Overridepublic String process(String request) {return dictionary.getOrDefault(request, "没找到");}public static void main(String[] args) throws IOException {EchoUDPServer server = new DictionaryUDPServer(1999);server.start();}
}

四.调试问题:

同时启动多个相同的代码: