/**
 * Класс для управления данными пользователя.
 */
public class User {
    /**
     * Имя пользователя, доступное только внутри класса.
     */
    private String name;

    /**
     * Возвращает имя пользователя.
     * @return Имя пользователя
     */
    public String getName() {
        return name;
    }
}

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class BufferedReaderExample {
    public static void main(String[] args) {
        try (BufferedReader reader = new BufferedReader(new FileReader("example.txt"))) {
            String line;
            while ((line = reader.readLine()) != null) {
                System.out.println(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.Iterator;

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

        ByteBuffer buffer = ByteBuffer.allocate(1024);

        while (true) {
            selector.select();
            Iterator<SelectionKey> keys = selector.selectedKeys().iterator();

            while (keys.hasNext()) {
                SelectionKey key = keys.next();
                keys.remove();

                if (key.isAcceptable()) {
                    SocketChannel client = serverChannel.accept();
                    client.configureBlocking(false);
                    client.register(selector, SelectionKey.OP_READ);
                } else if (key.isReadable()) {
                    SocketChannel client = (SocketChannel) key.channel();
                    buffer.clear();
                    int bytesRead = client.read(buffer);
                    if (bytesRead == -1) {
                        client.close();
                    } else {
                        buffer.flip();
                        client.write(buffer);
                    }
                }
            }
        }
    }
}

import java.nio.ByteBuffer;
import java.nio.channels.AsynchronousFileChannel;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
import java.util.concurrent.Future;

public class AsyncFileRead {
    public static void main(String[] args) throws Exception {
        Path path = Paths.get("example.txt");
        AsynchronousFileChannel fileChannel = AsynchronousFileChannel.open(path, StandardOpenOption.READ);
        ByteBuffer buffer = ByteBuffer.allocate(1024);

        Future<Integer> result = fileChannel.read(buffer, 0);
        while (!result.isDone()) {
            System.out.println("Waiting for read operation...");
            Thread.sleep(100);
        }

        buffer.flip();
        byte[] data = new byte[buffer.limit()];
        buffer.get(data);
        System.out.println(new String(data));
        fileChannel.close();
    }
}