Linux中Java如何进行网络编程 - 问答

在Linux环境下，使用Java进行网络编程主要涉及到以下几个方面：

1. 基础知识

Socket编程：Java提供了java.net.Socket和java.net.ServerSocket类来进行基于TCP的网络通信。
URL和URLConnection：用于HTTP请求和响应的处理。
NIO（非阻塞I/O）：使用java.nio包中的类进行高效的网络通信。

2. Socket编程示例

服务器端

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

public class SimpleServer {
    public static void main(String[] args) {
        try (ServerSocket serverSocket = new ServerSocket(8080)) {
            System.out.println("Server is listening on port 8080");
            while (true) {
                Socket clientSocket = serverSocket.accept();
                System.out.println("New client connected");

                BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
                PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);

                String inputLine;
                while ((inputLine = in.readLine()) != null) {
                    System.out.println("Received from client: " + inputLine);
                    out.println("Server received: " + inputLine);
                }

                clientSocket.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

客户端

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

public class SimpleClient {
    public static void main(String[] args) {
        try (Socket socket = new Socket("localhost", 8080)) {
            BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            PrintWriter out = new PrintWriter(socket.getOutputStream(), true);

            out.println("Hello, Server!");
            String response = in.readLine();
            System.out.println("Server response: " + response);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

3. URL和URLConnection示例

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

public class HttpClient {
    public static void main(String[] args) {
        try {
            URL url = new URL("http://example.com");
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("GET");

            int responseCode = connection.getResponseCode();
            System.out.println("Response Code: " + responseCode);

            BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            String inputLine;
            StringBuilder response = new StringBuilder();

            while ((inputLine = in.readLine()) != null) {
                response.append(inputLine);
            }
            in.close();

            System.out.println("Response Body: " + response.toString());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

4. NIO示例

import java.io.*;
import java.net.*;
import java.nio.*;
import java.nio.channels.*;
import java.util.*;

public class NIOServer {
    public static void main(String[] args) throws IOException {
        Selector selector = Selector.open();
        ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
        serverSocketChannel.bind(new InetSocketAddress(8080));
        serverSocketChannel.configureBlocking(false);
        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);

        while (true) {
            selector.select();
            Set<SelectionKey> selectedKeys = selector.selectedKeys();
            Iterator<SelectionKey> iter = selectedKeys.iterator();
            while (iter.hasNext()) {
                SelectionKey key = iter.next();

                if (key.isAcceptable()) {
                    handleAccept(key, selector);
                } else if (key.isReadable()) {
                    handleRead(key);
                }

                iter.remove();
            }
        }
    }

    private static void handleAccept(SelectionKey key, Selector selector) throws IOException {
        ServerSocketChannel serverSocketChannel = (ServerSocketChannel) key.channel();
        SocketChannel clientChannel = serverSocketChannel.accept();
        clientChannel.configureBlocking(false);
        clientChannel.register(selector, SelectionKey.OP_READ);
    }

    private static void handleRead(SelectionKey key) throws IOException {
        SocketChannel clientChannel = (SocketChannel) key.channel();
        ByteBuffer buffer = ByteBuffer.allocate(1024);
        int bytesRead = clientChannel.read(buffer);

        if (bytesRead > 0) {
            buffer.flip();
            byte[] data = new byte[buffer.remaining()];
            buffer.get(data);
            String message = new String(data).trim();
            System.out.println("Received: " + message);

            ByteBuffer responseBuffer = ByteBuffer.wrap(("Echo: " + message).getBytes());
            clientChannel.write(responseBuffer);
        } else if (bytesRead == -1) {
            clientChannel.close();
        }
    }
}

5. 注意事项

异常处理：网络编程中异常处理非常重要，确保程序的健壮性。
资源管理：使用try-with-resources语句来确保资源（如Socket、InputStream、OutputStream等）在使用完毕后自动关闭。
线程安全：在高并发环境下，确保共享资源的线程安全性。

通过以上步骤和示例代码，你可以在Linux环境下使用Java进行基本的网络编程。根据具体需求，你可以进一步扩展和优化这些示例。

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