Netty

public static void main(String[] args) {
    // 获取文件channel
    // 1.从文件流获取  2. new RandomAccessFile().getChannel()
    try (FileChannel channel = new FileInputStream("pom.xml").getChannel()) {
        // 分配一个缓冲区
        ByteBuffer allocate = ByteBuffer.allocate(1024);
        // 读取文件
        while (channel.read(allocate) != -1) {
            // 切换为读模式
            allocate.flip();
            // 读取数据
            while (allocate.hasRemaining()) {
                logger.info(String.valueOf((char) allocate.get()));
            }
            // 切换为写模式
            allocate.clear();
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
}

import io.netty.util.internal.StringUtil;

import java.nio.ByteBuffer;

import static io.netty.util.internal.MathUtil.isOutOfBounds;
import static io.netty.util.internal.StringUtil.NEWLINE;

public class ByteBufferUtil {
    private static final char[] BYTE2CHAR = new char[256];
    private static final char[] HEXDUMP_TABLE = new char[256 * 4];
    private static final String[] HEXPADDING = new String[16];
    private static final String[] HEXDUMP_ROWPREFIXES = new String[65536 >>> 4];
    private static final String[] BYTE2HEX = new String[256];
    private static final String[] BYTEPADDING = new String[16];

    static {
        final char[] DIGITS = "0123456789abcdef".toCharArray();
        for (int i = 0; i < 256; i++) {
            HEXDUMP_TABLE[i << 1] = DIGITS[i >>> 4 & 0x0F];
            HEXDUMP_TABLE[(i << 1) + 1] = DIGITS[i & 0x0F];
        }

        int i;

        // Generate the lookup table for hex dump paddings
        for (i = 0; i < HEXPADDING.length; i++) {
            int padding = HEXPADDING.length - i;
            StringBuilder buf = new StringBuilder(padding * 3);
            for (int j = 0; j < padding; j++) {
                buf.append("   ");
            }
            HEXPADDING[i] = buf.toString();
        }

        // Generate the lookup table for the start-offset header in each row (up to 64KiB).
        for (i = 0; i < HEXDUMP_ROWPREFIXES.length; i++) {
            StringBuilder buf = new StringBuilder(12);
            buf.append(NEWLINE);
            buf.append(Long.toHexString(i << 4 & 0xFFFFFFFFL | 0x100000000L));
            buf.setCharAt(buf.length() - 9, '|');
            buf.append('|');
            HEXDUMP_ROWPREFIXES[i] = buf.toString();
        }

        // Generate the lookup table for byte-to-hex-dump conversion
        for (i = 0; i < BYTE2HEX.length; i++) {
            BYTE2HEX[i] = ' ' + StringUtil.byteToHexStringPadded(i);
        }

        // Generate the lookup table for byte dump paddings
        for (i = 0; i < BYTEPADDING.length; i++) {
            int padding = BYTEPADDING.length - i;
            StringBuilder buf = new StringBuilder(padding);
            for (int j = 0; j < padding; j++) {
                buf.append(' ');
            }
            BYTEPADDING[i] = buf.toString();
        }

        // Generate the lookup table for byte-to-char conversion
        for (i = 0; i < BYTE2CHAR.length; i++) {
            if (i <= 0x1f || i >= 0x7f) {
                BYTE2CHAR[i] = '.';
            } else {
                BYTE2CHAR[i] = (char) i;
            }
        }
    }

    /**
     * 打印所有内容
     * @param buffer
     */
    public static void debugAll(ByteBuffer buffer) {
        int oldlimit = buffer.limit();
        buffer.limit(buffer.capacity());
        StringBuilder origin = new StringBuilder(256);
        appendPrettyHexDump(origin, buffer, 0, buffer.capacity());
        System.out.println("+--------+-------------------- all ------------------------+----------------+");
        System.out.printf("position: [%d], limit: [%d]\n", buffer.position(), oldlimit);
        System.out.println(origin);
        buffer.limit(oldlimit);
    }

    /**
     * 打印可读取内容
     * @param buffer
     */
    public static void debugRead(ByteBuffer buffer) {
        StringBuilder builder = new StringBuilder(256);
        appendPrettyHexDump(builder, buffer, buffer.position(), buffer.limit() - buffer.position());
        System.out.println("+--------+-------------------- read -----------------------+----------------+");
        System.out.printf("position: [%d], limit: [%d]\n", buffer.position(), buffer.limit());
        System.out.println(builder);
    }

    public static void appendPrettyHexDump(StringBuilder dump, ByteBuffer buf, int offset, int length) {
        if (isOutOfBounds(offset, length, buf.capacity())) {
            throw new IndexOutOfBoundsException(
                    "expected: " + "0 <= offset(" + offset + ") <= offset + length(" + length
                            + ") <= " + "buf.capacity(" + buf.capacity() + ')');
        }
        if (length == 0) {
            return;
        }
        dump.append(
                "         +-------------------------------------------------+" +
                        NEWLINE + "         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |" +
                        NEWLINE + "+--------+-------------------------------------------------+----------------+");

        final int startIndex = offset;
        final int fullRows = length >>> 4;
        final int remainder = length & 0xF;

        // Dump the rows which have 16 bytes.
        for (int row = 0; row < fullRows; row++) {
            int rowStartIndex = (row << 4) + startIndex;

            // Per-row prefix.
            appendHexDumpRowPrefix(dump, row, rowStartIndex);

            // Hex dump
            int rowEndIndex = rowStartIndex + 16;
            for (int j = rowStartIndex; j < rowEndIndex; j++) {
                dump.append(BYTE2HEX[getUnsignedByte(buf, j)]);
            }
            dump.append(" |");

            // ASCII dump
            for (int j = rowStartIndex; j < rowEndIndex; j++) {
                dump.append(BYTE2CHAR[getUnsignedByte(buf, j)]);
            }
            dump.append('|');
        }

        // Dump the last row which has less than 16 bytes.
        if (remainder != 0) {
            int rowStartIndex = (fullRows << 4) + startIndex;
            appendHexDumpRowPrefix(dump, fullRows, rowStartIndex);

            // Hex dump
            int rowEndIndex = rowStartIndex + remainder;
            for (int j = rowStartIndex; j < rowEndIndex; j++) {
                dump.append(BYTE2HEX[getUnsignedByte(buf, j)]);
            }
            dump.append(HEXPADDING[remainder]);
            dump.append(" |");

            // Ascii dump
            for (int j = rowStartIndex; j < rowEndIndex; j++) {
                dump.append(BYTE2CHAR[getUnsignedByte(buf, j)]);
            }
            dump.append(BYTEPADDING[remainder]);
            dump.append('|');
        }

        dump.append(NEWLINE +
                "+--------+-------------------------------------------------+----------------+");
    }

    public static void appendHexDumpRowPrefix(StringBuilder dump, int row, int rowStartIndex) {
        if (row < HEXDUMP_ROWPREFIXES.length) {
            dump.append(HEXDUMP_ROWPREFIXES[row]);
        } else {
            dump.append(NEWLINE);
            dump.append(Long.toHexString(rowStartIndex & 0xFFFFFFFFL | 0x100000000L));
            dump.setCharAt(dump.length() - 9, '|');
            dump.append('|');
        }
    }

    public static short getUnsignedByte(ByteBuffer buffer, int index) {
        return (short) (buffer.get(index) & 0xFF);
    }
}

public static void main(String[] args) {
    String str = "hello world";
    byte[] bytes = str.getBytes();
    ByteBuffer buffer = ByteBuffer.allocate(bytes.length);
    buffer.put(bytes);

    ByteBuffer helloWorld = StandardCharsets.UTF_8.encode("hello world");


    ByteBuffer wrap = ByteBuffer.wrap(bytes);

    // 转为字符串
    String decode = StandardCharsets.UTF_8.decode(wrap).toString();
    System.out.println(decode);

    buffer.flip();
    String decode1 = StandardCharsets.UTF_8.decode(buffer).toString();
    System.out.println(decode1);
}

public static void main(String[] args) {
    ByteBuffer b1 = ByteBuffer.allocate(3);
    ByteBuffer b2 = ByteBuffer.allocate(3);
    ByteBuffer b3 = ByteBuffer.allocate(5);
    try (FileChannel channel = new RandomAccessFile("words.txt", "r").getChannel()) {
        channel.read(new ByteBuffer[] { b1, b2, b3});
        b1.flip();
        b2.flip();
        b3.flip();
        while (b1.hasRemaining()) {
            System.out.print((char) b1.get());
        }
        while (b2.hasRemaining()) {
            System.out.print((char) b2.get());
        }
        while (b3.hasRemaining()) {
            System.out.print((char) b3.get());
        }
    } catch (IOException e) {
    }
}

public static void main(String[] args) {
    ByteBuffer b1 = StandardCharsets.UTF_8.encode("hello ");
    ByteBuffer b2 = StandardCharsets.UTF_8.encode("world ");
    ByteBuffer b3 = StandardCharsets.UTF_8.encode("你好");
    try (FileChannel channel = new RandomAccessFile("words1.txt", "rw").getChannel()) {
        channel.write(new ByteBuffer[] { b1, b2, b3 });
    } catch (IOException e) {

    }
}

public static void main(String[] args) {
    ByteBuffer source = ByteBuffer.allocate(32);
    source.put("Hello,World\nI'm zhangsan\nHo".getBytes());
    split(source);
    source.put("w are you?\n".getBytes());
    split(source);
}

private static void split(ByteBuffer source) {
    source.flip();
    for (int i = 0; i < source.limit(); i++) {
        if (source.get(i) == '\n') {
            int length = i + 1 - source.position();
            ByteBuffer target = ByteBuffer.allocate(length);
            for (int j = 0; j < length; j++) {
                target.put(source.get());
            }
            target.flip();
            System.out.println(StandardCharsets.UTF_8.decode(target).toString());
        }
    }
    source.compact();
}

Path path = Paths.get("helloword/data.txt");
System.out.println(Files.exists(path));

Path path = Paths.get("helloword/d1");
Files.createDirectory(path);

Path source = Paths.get("helloword/data.txt");
Path target = Paths.get("helloword/target.txt");

Files.copy(source, target);

Selector selector = Selector.open();

channel.configureBlocking(false);
SelectorKey key = channel.register(selector, 绑定事件类型);

int count = selector.select();

import lombok.extern.slf4j.Slf4j;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.SocketException;
import java.nio.ByteBuffer;
import java.nio.channels.*;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import static utils.ByteBufferUtil.debugRead;

@Slf4j
public class C2_Server {
    public static void main(String[] args) throws IOException {
        ServerSocketChannel ssc = ServerSocketChannel.open();
        ssc.bind(new InetSocketAddress(8080));
        ssc.configureBlocking(false);

        // 1. 创建Selector
        Selector selector = Selector.open();
        // 1. 注册Selector事件
        SelectionKey sscKey = ssc.register(selector, 0, null);
        sscKey.interestOps(SelectionKey.OP_ACCEPT);

        List<ServerSocketChannel> channels = new ArrayList<>();
        while(true) {
            // 2. select 方法
            selector.select();

            // 3. 处理事件
            Iterator<SelectionKey> iter = selector.selectedKeys().iterator();
            while(iter.hasNext()) {
		            SelectionKey key = iter.next();

		            // 4. 处理accept事件
		            ServerSocketChannel channel = (ServerSocketChannel) key.channel();
		            log.debug("key: {}", key);
		            SocketChannel sc = channel.accept();
		            log.debug("sc: {}", sc);
            }
        }
    }
}

ServerSocketChannel ssc = ServerSocketChannel.open();
ssc.bind(new InetSocketAddress(8080));
ssc.configureBlocking(false);

// 1. 注册channel
Selector selector = Selector.open();
SelectionKey sscKey = ssc.register(selector, 0, null);
sscKey.interestOps(SelectionKey.OP_ACCEPT);

List<ServerSocketChannel> channels = new ArrayList<>();
while(true) {
    // 2. select 方法
    selector.select();

    // 3. 处理事件
    Iterator<SelectionKey> iter = selector.selectedKeys().iterator();
    while(iter.hasNext()) {
        SelectionKey key = iter.next();
        // 必须要移除这个事件
        iter.remove();

        if(key.isAcceptable()) {
            // 处理accept事件
            ServerSocketChannel channel = (ServerSocketChannel) key.channel();
            log.debug("key: {}", key);
            SocketChannel sc = channel.accept();
            sc.configureBlocking(false);
            SelectionKey scKey = sc.register(selector, 0, null);
            scKey.interestOps(SelectionKey.OP_READ);
            log.debug("sc: {}", sc);
        } else if(key.isReadable()) {
            // 处理read事件
            try {
                ByteBuffer buffer = ByteBuffer.allocate(16);
                SocketChannel channel = (SocketChannel) key.channel();
                int len = channel.read(buffer);

                if(len == -1) {
                    key.cancel();
                    System.out.println("主动断开连接");
                } else {
                    buffer.flip();
                    debugRead(buffer);
                }
            } catch (SocketException e) {
                e.printStackTrace();
                key.cancel();
                System.out.println("强制断开连接");
            }
        }
    }
}

public static void main(String[] args) throws IOException {
    ServerSocketChannel ssc = ServerSocketChannel.open();
    ssc.bind(new InetSocketAddress(8080));
    ssc.configureBlocking(false);

    // 1. 注册channel
    Selector selector = Selector.open();
    SelectionKey sscKey = ssc.register(selector, 0, null);
    sscKey.interestOps(SelectionKey.OP_ACCEPT);

    List<ServerSocketChannel> channels = new ArrayList<>();
    while(true) {
        // 2. select 方法
        selector.select();

        // 3. 处理事件
        Iterator<SelectionKey> iter = selector.selectedKeys().iterator();
        while(iter.hasNext()) {
            SelectionKey key = iter.next();
            iter.remove();

            if(key.isAcceptable()) {
                // 处理accept事件
                ServerSocketChannel channel = (ServerSocketChannel) key.channel();
                log.debug("key: {}", key);
                SocketChannel sc = channel.accept();
                sc.configureBlocking(false);

                ByteBuffer buffer = ByteBuffer.allocate(8);
                SelectionKey scKey = sc.register(selector, 0, buffer);
                scKey.interestOps(SelectionKey.OP_READ);
                log.debug("sc: {}", sc);
            } else if(key.isReadable()) {
                // 处理read事件
                try {
                    SocketChannel channel = (SocketChannel) key.channel();
                    ByteBuffer buffer = (ByteBuffer) key.attachment();
                    int len = channel.read(buffer);
                    System.out.println(len);

                    if(len == -1) {
                        key.cancel();
                        System.out.println("主动断开连接");
                    } else {
                        split(buffer);
                        if(buffer.position() == buffer.limit()) {
                            ByteBuffer newBuffer = ByteBuffer.allocate(buffer.capacity() * 2);
                            buffer.flip();
                            newBuffer.put(buffer);
                            key.attach(newBuffer);
                        }
                    }
                } catch (SocketException e) {
                    e.printStackTrace();
                    key.cancel();
                    System.out.println("强制断开连接");
                }
            }
        }
    }
}
private static void split(ByteBuffer source) {
    source.flip();
    for (int i = 0; i < source.limit(); i++) {
        // 找到一条完整消息
        if (source.get(i) == '\n') {
            int length = i + 1 - source.position();
            // 把这条完整消息存入新的 ByteBuffer
            ByteBuffer target = ByteBuffer.allocate(length);
            // 从 source 读，向 target 写
            for (int j = 0; j < length; j++) {
                target.put(source.get());
            }
            debugAll(target);
        }
    }
    source.compact(); // 0123456789abcdef  position 16 limit 16
}

File f = new File("helloword/data.txt");
RandomAccessFile file = new RandomAccessFile(file, "r");

byte[] buf = new byte[(int)f.length()];
file.read(buf);

Socket socket = ...;
socket.getOutputStream().write(buf);

@Slf4j
public class EventLoopGroupDemo {
    public static void main(String[] args) {
        // 内部创建了两个EventLoop，每个EventLoop维护一个线程
        NioEventLoopGroup group = new NioEventLoopGroup(2);
        System.out.println(group.next());
        System.out.println(group.next());
        System.out.println(group.next());
        // 一个EventLoop进行普通任务
        group.next().submit(() -> {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            log.debug("ok");
        });
        log.debug("main ok");
    }
}

// 输出结果
io.netty.channel.nio.NioEventLoop@30ee2816
io.netty.channel.nio.NioEventLoop@31d7b7bf
io.netty.channel.nio.NioEventLoop@30ee2816
17:05:00.314 [main] DEBUG org.example.net.netty.EventLoopGroupDemo - main ok
17:05:01.329 [nioEventLoopGroup-2-1] DEBUG org.example.net.netty.EventLoopGroupDemo - ok