Java 之网络编程小案例

1. 多发多收

描述： 编写一个简单的聊天程序，客户端可以向服务器发送多条消息，服务器可以接收所有消息并回复。

代码示例：

服务器端 (Server.java):

import java.io.*;
import java.net.*;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;public class Server {public static void main(String[] args) throws IOException {// 创建 ServerSocket 对象，监听指定端口ServerSocket serverSocket = new ServerSocket(8080);System.out.println("服务器启动，监听端口 8080");// 创建线程池，处理多个客户端连接ExecutorService executor = Executors.newFixedThreadPool(10);while (true) {// 阻塞等待客户端连接Socket socket = serverSocket.accept();System.out.println("客户端连接成功: " + socket.getInetAddress().getHostAddress());// 创建线程处理客户端连接executor.execute(new ClientHandler(socket));}}// 处理客户端连接的线程类static class ClientHandler implements Runnable {private Socket socket;public ClientHandler(Socket socket) {this.socket = socket;}@Overridepublic void run() {try (BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));PrintWriter out = new PrintWriter(socket.getOutputStream(), true)) {String message;while ((message = in.readLine()) != null) {System.out.println("收到客户端消息: " + message);out.println("服务器回复: " + message);}} catch (IOException e) {e.printStackTrace();}}}
}

客户端 (Client.java):

import java.io.*;
import java.net.*;public class Client {public static void main(String[] args) throws IOException {// 创建 Socket 对象，连接服务器Socket socket = new Socket("127.0.0.1", 8080);// 获取输入流和输出流BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));PrintWriter out = new PrintWriter(socket.getOutputStream(), true);// 发送多条消息for (int i = 1; i <= 5; i++) {out.println("客户端消息 " + i);System.out.println("发送消息: " + "客户端消息 " + i);// 接收服务器回复String response = in.readLine();System.out.println("接收回复: " + response);}// 关闭连接socket.close();}
}

运行步骤：

运行 Server.java，启动服务器。
运行 Client.java，启动客户端。
客户端会发送 5 条消息，服务器会逐条接收并回复。

2. 接收并回复

描述： 编写一个程序，服务器接收客户端发送的字符串，并将其反转后回复给客户端。

代码示例：

服务器端 (Server.java):

import java.io.*;
import java.net.*;public class Server {public static void main(String[] args) throws IOException {// 创建 ServerSocket 对象，监听指定端口ServerSocket serverSocket = new ServerSocket(8080);System.out.println("服务器启动，监听端口 8080");while (true) {// 阻塞等待客户端连接Socket socket = serverSocket.accept();System.out.println("客户端连接成功: " + socket.getInetAddress().getHostAddress());// 获取输入流和输出流BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));PrintWriter out = new PrintWriter(socket.getOutputStream(), true);// 接收客户端发送的消息String message = in.readLine();System.out.println("收到客户端消息: " + message);// 反转消息String reversedMessage = new StringBuilder(message).reverse().toString();// 将反转后的消息发送回客户端out.println(reversedMessage);System.out.println("发送回复: " + reversedMessage);// 关闭连接socket.close();}}
}

客户端 (Client.java):

import java.io.*;
import java.net.*;public class Client {public static void main(String[] args) throws IOException {// 创建 Socket 对象，连接服务器Socket socket = new Socket("127.0.0.1", 8080);// 获取输入流和输出流BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));PrintWriter out = new PrintWriter(socket.getOutputStream(), true);// 发送消息out.println("hello world");System.out.println("发送消息: hello world");// 接收服务器回复String response = in.readLine();System.out.println("接收回复: " + response);// 关闭连接socket.close();}
}

运行步骤：

运行 Server.java，启动服务器。
运行 Client.java，启动客户端。
客户端会发送 "hello world"，服务器会将它反转为 "dlrow olleh" 并回复给客户端。

3. 上传文件

描述： 编写一个程序，客户端上传文件到服务器，服务器保存文件到指定目录。

代码示例：

服务器端 (Server.java):

import java.io.*;
import java.net.*;public class Server {public static void main(String[] args) throws IOException {// 创建 ServerSocket 对象，监听指定端口ServerSocket serverSocket = new ServerSocket(8080);System.out.println("服务器启动，监听端口 8080");while (true) {// 阻塞等待客户端连接Socket socket = serverSocket.accept();System.out.println("客户端连接成功: " + socket.getInetAddress().getHostAddress());// 获取输入流和输出流InputStream in = socket.getInputStream();OutputStream out = socket.getOutputStream();// 接收文件名BufferedReader reader = new BufferedReader(new InputStreamReader(in));String fileName = reader.readLine();System.out.println("接收文件名: " + fileName);// 创建文件输出流File file = new File("upload/" + fileName); // 文件保存到 upload 目录FileOutputStream fileOutputStream = new FileOutputStream(file);// 接收文件内容byte[] buffer = new byte[1024];int bytesRead;while ((bytesRead = in.read(buffer)) != -1) {fileOutputStream.write(buffer, 0, bytesRead);}// 发送成功信息out.write("文件上传成功".getBytes());System.out.println("文件上传成功: " + fileName);// 关闭流和连接fileOutputStream.close();in.close();out.close();socket.close();}}
}

客户端 (Client.java):

import java.io.*;
import java.net.*;public class Client {public static void main(String[] args) throws IOException {// 创建 Socket 对象，连接服务器Socket socket = new Socket("127.0.0.1", 8080);// 获取输入流和输出流InputStream in = socket.getInputStream();OutputStream out = socket.getOutputStream();// 上传文件File file = new File("test.txt"); // 上传 test.txt 文件String fileName = file.getName();// 发送文件名PrintWriter writer = new PrintWriter(out, true);writer.println(fileName);// 发送文件内容FileInputStream fileInputStream = new FileInputStream(file);byte[] buffer = new byte[1024];int bytesRead;while ((bytesRead = fileInputStream.read(buffer)) != -1) {out.write(buffer, 0, bytesRead);}// 接收服务器回复byte[] response = new byte[1024];in.read(response);System.out.println("服务器回复: " + new String(response));// 关闭流和连接fileInputStream.close();in.close();out.close();socket.close();}
}

运行步骤：