Java 网络编程与网络通信基础

输出结果： 服务器端显示连接成功及消息接收，客户端显示响应内容。

结论：Socket 与 ServerSocket 是 Java 网络编程的基础，用于实现客户端与服务器之间的通信。

13.4 TCP/IP 通信的实现

TCP/IP 通信是可靠的、面向连接的通信方式。

13.4.1 服务器端的实现

示例：

import java.io.*;
import java.net.*;

public class TCPServer {
    public static void main(String[] args) {
        try {
            ServerSocket serverSocket = new ServerSocket(8888);
            System.out.println("服务器端启动成功，等待客户端连接...");
            while (true) {
                Socket socket = serverSocket.accept();
                System.out.println("客户端连接成功：" + socket.getInetAddress().getHostAddress());
                new Thread(() -> {
                    try {
                        BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
                        PrintWriter writer = new PrintWriter(socket.getOutputStream(), true);
                        String message = reader.readLine();
                        System.out.println("客户端消息：" + message);
                        writer.println("服务器端已收到消息：" + message);
                        reader.close();
                        writer.close();
                        socket.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }).start();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

结论：服务器端需创建线程处理客户端请求。

13.4.2 客户端的实现

示例：

import java.io.*;
import java.net.*;

public class TCPClient {
    public static void main(String[] args) {
        try {
            Socket socket = new Socket("localhost", 8888);
            System.out.println("客户端连接成功");
            BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            PrintWriter writer = new PrintWriter(socket.getOutputStream(), true);
            writer.println("Hello, Server!");
            String response = reader.readLine();
            System.out.println("服务器端响应：" + response);
            reader.close();
            writer.close();
            socket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

结论：客户端需与服务器端建立连接并发送数据。

13.5 UDP 通信的实现

UDP 通信是不可靠的、无连接的通信方式。

13.5.1 DatagramSocket 与 DatagramPacket 的定义

定义：DatagramSocket 表示 UDP 套接字，DatagramPacket 表示 UDP 数据包。

常用方法：

• DatagramSocket：send()、receive()、close()
• DatagramPacket：getData()、getLength()、getAddress()、getPort()

示例：

import java.io.*;
import java.net.*;

// 服务器端
public class UDPServer {
    public static void main(String[] args) {
        try {
            DatagramSocket socket = new DatagramSocket(8888);
            System.out.println("服务器端启动成功，等待客户端连接...");
            byte[] buffer = new byte[1024];
            DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
            socket.receive(packet);
            String message = new String(packet.getData(), 0, packet.getLength());
            System.out.println("客户端消息：" + message);
            String response = "服务器端已收到消息：" + message;
            byte[] responseBuffer = response.getBytes();
            DatagramPacket responsePacket = new DatagramPacket(responseBuffer, responseBuffer.length, packet.getAddress(), packet.getPort());
            socket.send(responsePacket);
            socket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

// 客户端
public class UDPClient {
    public static void main(String[] args) {
        try {
            DatagramSocket socket = new DatagramSocket();
            System.out.println("客户端启动成功");
            String message = "Hello, Server!";
            byte[] buffer = message.getBytes();
            InetAddress address = InetAddress.getByName("localhost");
            DatagramPacket packet = new DatagramPacket(buffer, buffer.length, address, 8888);
            socket.send(packet);
            byte[] responseBuffer = new byte[1024];
            DatagramPacket responsePacket = new DatagramPacket(responseBuffer, responseBuffer.length);
            socket.receive(responsePacket);
            String response = new String(responsePacket.getData(), 0, responsePacket.getLength());
            System.out.println("服务器端响应：" + response);
            socket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

结论：DatagramSocket 与 DatagramPacket 是 Java 中 UDP 通信的基础。

13.6 HTTP 通信的实现

HTTP 通信是基于 TCP/IP 的应用层通信方式。

13.6.1 URL 与 URLConnection 的定义

定义：URL 表示统一资源定位符，URLConnection 表示 URL 连接。

常用方法：

• URL：openConnection()、getProtocol()、getHost()、getPort()、getPath()
• URLConnection：getInputStream()、getOutputStream()、setRequestProperty()、getResponseCode()、getResponseMessage()

示例：

import java.io.*;
import java.net.*;

public class HTTPExample {
    public static void main(String[] args) {
        try {
            URL url = new URL("https://www.baidu.com");
            URLConnection connection = url.openConnection();
            connection.setRequestProperty("User-Agent", "Mozilla/5.0");
            BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            String line;
            StringBuffer response = new StringBuffer();
            while ((line = reader.readLine()) != null) {
                response.append(line);
            }
            reader.close();
            System.out.println("响应数据：" + response.toString());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

结论：URL 与 URLConnection 是 Java 中 HTTP 通信的基础。

13.7 网络编程的实际应用场景

实际开发中，网络编程广泛应用于文件传输、聊天、爬虫等场景。

示例：文件上传

import java.io.*;
import java.net.*;

// 文件上传服务器端
public class FileUploadServer {
    public static void main(String[] args) {
        try {
            ServerSocket serverSocket = new ServerSocket(8888);
            System.out.println("服务器端启动成功，等待客户端连接...");
            Socket socket = serverSocket.accept();
            System.out.println("客户端连接成功：" + socket.getInetAddress().getHostAddress());
            BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            DataInputStream dataInputStream = new DataInputStream(socket.getInputStream());
            FileOutputStream fileOutputStream = new FileOutputStream("uploaded_file.txt");
            String fileName = reader.readLine();
            System.out.println("文件名：" + fileName);
            byte[] buffer = new byte[1024];
            int length;
            while ((length = dataInputStream.read(buffer)) > 0) {
                fileOutputStream.write(buffer, 0, length);
            }
            fileOutputStream.close();
            dataInputStream.close();
            reader.close();
            socket.close();
            serverSocket.close();
            System.out.println("文件上传成功");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

// 文件上传客户端
public class FileUploadClient {
    public static void main(String[] args) {
        try {
            Socket socket = new Socket("localhost", 8888);
            System.out.println("客户端连接成功");
            PrintWriter writer = new PrintWriter(socket.getOutputStream(), true);
            DataOutputStream dataOutputStream = new DataOutputStream(socket.getOutputStream());
            FileInputStream fileInputStream = new FileInputStream("test.txt");
            String fileName = "test.txt";
            writer.println(fileName);
            byte[] buffer = new byte[1024];
            int length;
            while ((length = fileInputStream.read(buffer)) > 0) {
                dataOutputStream.write(buffer, 0, length);
            }
            fileInputStream.close();
            dataOutputStream.close();
            writer.close();
            socket.close();
            System.out.println("文件上传成功");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

结论：根据实际问题选择合适的网络编程方法。

总结

本章学习了 Java 网络编程与网络通信基础，包括套接字编程、TCP/IP 通信、UDP 通信、HTTP 通信的实现方法。重点掌握了 Socket、ServerSocket、DatagramSocket、DatagramPacket、URL、URLConnection 等核心类的使用，以及在网络文件传输等实际场景中的应用。