package org.example.demo1;
import lombok.extern.slf4j.Slf4j;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
@Slf4j
public class ChannelDemo1 {
    public static void main(String[] args) {
        try (FileChannel channel = new FileInputStream("data.txt").getChannel()) {
            ByteBuffer buffer = ByteBuffer.allocate(10);
            do {
                // 向 buffer 寫入
                int len = channel.read(buffer);
                log.debug("讀到字節(jié)數(shù)：{}", len);
                if (len == -1) {
                    break;
                }
                // 切換 buffer 讀模式
                buffer.flip();
                while(buffer.hasRemaining()) {
                    byte b = buffer.get();
                    log.debug("實(shí)際字節(jié){}", (char)b);
                }
                // 切換 buffer 寫模式
                buffer.clear();
            } while (true);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

package org.example.utils;
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;
            }
        }
    }
    /**
     * 打印所有內(nèi)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);
    }
    /**
     * 打印可讀取內(nèi)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);
    }
    private 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 +
                "+--------+-------------------------------------------------+----------------+");
    }
    private 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);
    }
}

package org.example.demo1;
import java.nio.ByteBuffer;
import static org.example.utils.ByteBufferUtil.debugAll;
public class TestByteBufferReadWrite {
    public static void main(String[] args){
        ByteBuffer byteBuffer = ByteBuffer.allocate(10);
        byteBuffer.put((byte) 0x61);// a
        debugAll(byteBuffer);
        byteBuffer.put(new byte[]{0x62,0x63,0x64});
        debugAll(byteBuffer);
        byteBuffer.get();
        debugAll(byteBuffer);
        //切換為讀的狀態(tài)
        byteBuffer.flip();
        byteBuffer.get();
        debugAll(byteBuffer);
        byteBuffer.compact();
        debugAll(byteBuffer);
    }
}

Bytebuffer buf = ByteBuffer.allocate(16);

package org.example.demo1;
import java.nio.ByteBuffer;
public class TestByteBufferAllocate {
    public static void main(String[] args){
        System.out.println(ByteBuffer.allocate(16).getClass());
        System.out.println(ByteBuffer.allocateDirect(16).getClass());
    }
}

int readBytes = channel.read(buf);

buf.put((byte)127);

int writeBytes = channel.write(buf);

byte b = buf.get();

package org.example.demo1;
import java.nio.ByteBuffer;
import static org.example.utils.ByteBufferUtil.debugAll;
public class TestByteBufferRead {
    public static void main(String[] args){
        ByteBuffer buffer = ByteBuffer.allocate(10);
        buffer.put(new byte[]{'a','b','c','d'});
        buffer.flip();
        //rewind 從頭開始讀
        buffer.get(new  byte[4]);
        debugAll(buffer);
        System.out.println("===============================rewind================================");
        buffer.rewind();
        System.out.println((char)buffer.get());
    }
}

package org.example.demo1;
import java.nio.ByteBuffer;
import static org.example.utils.ByteBufferUtil.debugAll;
public class TestByteBufferRead {
    public static void main(String[] args){
        ByteBuffer buffer = ByteBuffer.allocate(10);
        buffer.put(new byte[]{'a','b','c','d'});
        buffer.flip();
        //get(i) 不會(huì)改變讀索引的位置
        System.out.println((char) buffer.get(3));
        debugAll(buffer);
    }
}

package org.example.demo1;
import java.nio.ByteBuffer;
import static org.example.utils.ByteBufferUtil.debugAll;
public class TestByteBufferRead {
    public static void main(String[] args){
        ByteBuffer buffer = ByteBuffer.allocate(10);
        buffer.put(new byte[]{'a','b','c','d'});
        buffer.flip();
        //mark & reset
        //mark 做一個(gè)標(biāo)記，記錄position位置，reset 是將position重置到mark的位置
        System.out.println((char) buffer.get());
        System.out.println((char) buffer.get());
        buffer.mark();//加標(biāo)記，索引2的位置
        System.out.println((char) buffer.get());
        System.out.println((char) buffer.get());
        buffer.reset();//將position重置到索引2
        System.out.println((char) buffer.get());
        System.out.println((char) buffer.get());
    }
}

package org.example.demo1;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import static org.example.utils.ByteBufferUtil.debugAll;
public class TestByteBufferString {
    public static void main(String[] args){
        ByteBuffer buffer = ByteBuffer.allocate(16);
        buffer.put("hello".getBytes());
        debugAll(buffer);
        buffer.flip();
        CharBuffer charBuffer = StandardCharsets.UTF_8.decode(buffer);
        String charBufferstr = charBuffer.toString();
        System.out.println(charBufferstr);
        //2.Charset
        ByteBuffer buffer2 = StandardCharsets.UTF_8.encode("hello");
        debugAll(buffer2);
        CharBuffer charBuffer1 = StandardCharsets.UTF_8.decode(buffer2);
        String buffer1 = charBuffer1.toString();
        System.out.println(buffer1);
        //3.wrap
        ByteBuffer buffer3 = ByteBuffer.wrap("hello".getBytes());
        debugAll(buffer3);
        CharBuffer charBuffer3 = StandardCharsets.UTF_8.decode(buffer3);
        String bufferstr3 = charBuffer3.toString();
        System.out.println(bufferstr3);
    }
}

package org.example.demo1;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import static org.example.utils.ByteBufferUtil.debugAll;
public class TestByteBufferReads {
    public static void main(String[] args){
        try (RandomAccessFile file = new RandomAccessFile("parts.txt", "r")) {
            FileChannel channel = file.getChannel();
            ByteBuffer a = ByteBuffer.allocate(3);
            ByteBuffer b = ByteBuffer.allocate(3);
            ByteBuffer c = ByteBuffer.allocate(5);
            channel.read(new ByteBuffer[]{a, b, c});
            a.flip();
            b.flip();
            c.flip();
            debugAll(a);
            debugAll(b);
            debugAll(c);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

package org.example.demo1;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.StandardCharsets;
public class TestGatheringWrites {
    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("words2.txt","rw").getChannel()){
            channel.write(new ByteBuffer[]{b1,b2,b3});
        }catch (IOException ex){
        }
    }
}

public static void main(String[] args) {
    ByteBuffer source = ByteBuffer.allocate(32);
    //                     11            24
    source.put("Hello,world\nI'm zhangsan\nHo".getBytes());
    split(source);
    source.put("w are you?\nhaha!\n".getBytes());
    split(source);
}
private static void split(ByteBuffer source) {
    source.flip();
    int oldLimit = source.limit();
    for (int i = 0; i < oldLimit; i++) {
        if (source.get(i) == '\n') {
            System.out.println(i);
            ByteBuffer target = ByteBuffer.allocate(i + 1 - source.position());
            // 0 ~ limit
            source.limit(i + 1);
            target.put(source); // 從source 讀，向 target 寫
            debugAll(target);
            source.limit(oldLimit);
        }
    }
    source.compact();
}