Network programming practice of Java underlying technology: how to implement Socket communication and NIO

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

public class Client {
    public static void main(String[] args) {
        try {
            // 创建Socket对象，并指定服务器的IP地址和端口号
            Socket socket = new Socket("127.0.0.1", 8888);
            
            // 获取输出流，用于向服务器发送数据
            OutputStream os = socket.getOutputStream();
            PrintWriter pw = new PrintWriter(os);
            
            // 向服务器发送数据
            pw.write("Hello, Server!");
            pw.flush();
            
            // 关闭输出流和Socket连接
            pw.close();
            os.close();
            socket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

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

public class Server {
    public static void main(String[] args) {
        try {
            // 创建ServerSocket对象，并指定监听的端口号
            ServerSocket serverSocket = new ServerSocket(8888);
            
            // 等待客户端连接
            Socket socket = serverSocket.accept();
            
            // 获取输入流，用于接收客户端发送的数据
            InputStream is = socket.getInputStream();
            BufferedReader br = new BufferedReader(new InputStreamReader(is));
            
            // 接收客户端发送的数据
            System.out.println("Received from client: " + br.readLine());
            
            // 关闭输入流、Socket连接和ServerSocket连接
            br.close();
            is.close();
            socket.close();
            serverSocket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

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

public class Client {
    public static void main(String[] args) {
        try {
            // 创建SocketChannel对象，并连接服务器
            SocketChannel socketChannel = SocketChannel.open();
            socketChannel.connect(new InetSocketAddress("127.0.0.1", 8888));
            
            // 发送数据给服务器
            String message = "Hello, Server!";
            ByteBuffer buffer = ByteBuffer.wrap(message.getBytes());
            socketChannel.write(buffer);

            // 关闭SocketChannel连接
            socketChannel.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

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

public class Server {
    public static void main(String[] args) {
        try {
            // 创建ServerSocketChannel对象，并绑定监听的端口号
            ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
            serverSocketChannel.bind(new InetSocketAddress(8888));
            
            // 设置为非阻塞模式
            serverSocketChannel.configureBlocking(false);

            // 创建Selector对象，并将ServerSocketChannel注册到Selector上
            Selector selector = Selector.open();
            serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
            
            while (true) {
                // 阻塞式等待就绪的事件
                selector.select();
                
                // 获取就绪的事件集合
                Set<SelectionKey> selectedKeys = selector.selectedKeys();
                Iterator<SelectionKey> iterator = selectedKeys.iterator();
                
                // 处理就绪事件
                while (iterator.hasNext()) {
                    SelectionKey key = iterator.next();
                    
                    // 接收客户端连接请求
                    if (key.isAcceptable()) {
                        ServerSocketChannel serverChannel = (ServerSocketChannel) key.channel();
                        SocketChannel socketChannel = serverChannel.accept();
                        
                        // 设置为非阻塞模式
                        socketChannel.configureBlocking(false);
                        
                        // 注册读事件到Selector上
                        socketChannel.register(selector, SelectionKey.OP_READ);
                    }
                    
                    // 读取客户端发送的数据
                    if (key.isReadable()) {
                        SocketChannel socketChannel = (SocketChannel) key.channel();
                        ByteBuffer buffer = ByteBuffer.allocate(1024);

                        // 读取数据到缓冲区
                        int bytesRead = socketChannel.read(buffer);
                        if (bytesRead > 0) {
                            buffer.flip();

                            // 提取缓冲区中的数据
                            byte[] data = new byte[bytesRead];
                            buffer.get(data);
                            String message = new String(data);
                            System.out.println("Received from client: " + message);
                        }

                        // 关闭客户端连接
                        socketChannel.close();
                    }

                    // 从处理集合中移除当前就绪的事件
                    iterator.remove();
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}