Java网络编程基础

引言

网络编程是Java的重要应用领域。本文介绍Java网络编程的基础知识和实战应用。

一、TCP Socket编程

1.1 服务器端

public class TCPServer {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = new ServerSocket(8080);
        System.out.println("服务器启动，监听端口8080...");
        
        while (true) {
            Socket socket = serverSocket.accept();
            System.out.println("客户端连接: " + socket.getInetAddress());
            
            // 读取客户端消息
            BufferedReader reader = new BufferedReader(
                new InputStreamReader(socket.getInputStream()));
            String message = reader.readLine();
            System.out.println("收到消息: " + message);
            
            // 发送响应
            PrintWriter writer = new PrintWriter(socket.getOutputStream(), true);
            writer.println("服务器收到: " + message);
            
            socket.close();
        }
    }
}

1.2 客户端

public class TCPClient {
    public static void main(String[] args) throws IOException {
        Socket socket = new Socket("localhost", 8080);
        
        // 发送消息
        PrintWriter writer = new PrintWriter(socket.getOutputStream(), true);
        writer.println("Hello Server!");
        
        // 接收响应
        BufferedReader reader = new BufferedReader(
            new InputStreamReader(socket.getInputStream()));
        String response = reader.readLine();
        System.out.println("服务器响应: " + response);
        
        socket.close();
    }
}

二、UDP Socket编程

2.1 UDP服务器

public class UDPServer {
    public static void main(String[] args) throws IOException {
        DatagramSocket socket = new DatagramSocket(9999);
        byte[] buffer = new byte[1024];
        
        while (true) {
            DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
            socket.receive(packet);
            
            String message = new String(packet.getData(), 0, packet.getLength());
            System.out.println("收到消息: " + message);
            
            // 发送响应
            String response = "服务器收到";
            byte[] data = response.getBytes();
            DatagramPacket sendPacket = new DatagramPacket(
                data, data.length, packet.getAddress(), packet.getPort());
            socket.send(sendPacket);
        }
    }
}

三、HTTP请求

// 发送GET请求
public String sendGet(String url) throws IOException {
    HttpURLConnection conn = (HttpURLConnection) new URL(url).openConnection();
    conn.setRequestMethod("GET");
    conn.setConnectTimeout(5000);
    
    int responseCode = conn.getResponseCode();
    if (responseCode == 200) {
        BufferedReader reader = new BufferedReader(
            new InputStreamReader(conn.getInputStream()));
        StringBuilder response = new StringBuilder();
        String line;
        while ((line = reader.readLine()) != null) {
            response.append(line);
        }
        reader.close();
        return response.toString();
    }
    return null;
}

// 发送POST请求
public String sendPost(String url, String params) throws IOException {
    HttpURLConnection conn = (HttpURLConnection) new URL(url).openConnection();
    conn.setRequestMethod("POST");
    conn.setDoOutput(true);
    
    OutputStream os = conn.getOutputStream();
    os.write(params.getBytes());
    os.flush();
    
    // 读取响应
    BufferedReader reader = new BufferedReader(
        new InputStreamReader(conn.getInputStream()));
    StringBuilder response = new StringBuilder();
    String line;
    while ((line = reader.readLine()) != null) {
        response.append(line);
    }
    reader.close();
    return response.toString();
}

四、多线程服务器

public class MultiThreadServer {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = new ServerSocket(8080);
        System.out.println("多线程服务器启动...");
        
        while (true) {
            Socket socket = serverSocket.accept();
            new Thread(new ClientHandler(socket)).start();
        }
    }
}

class ClientHandler implements Runnable {
    private Socket socket;
    
    public ClientHandler(Socket socket) {
        this.socket = socket;
    }
    
    @Override
    public void run() {
        try {
            BufferedReader reader = new BufferedReader(
                new InputStreamReader(socket.getInputStream()));
            PrintWriter writer = new PrintWriter(socket.getOutputStream(), true);
            
            String message = reader.readLine();
            System.out.println("处理消息: " + message);
            
            writer.println("服务器响应: " + message);
            
            socket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

总结

Java网络编程核心：

1. TCP：可靠的面向连接通信
2. UDP：快速的无连接通信
3. HTTP：应用层协议
4. 多线程：并发处理客户端请求

参考资料

• 《Java网络编程》
• Java Networking Tutorial