Netty—— AIO示例代码

Posted 2022-11-02 小志的博客

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一、AIO 概述

1.1、AIO 用来解决数据复制阶段的阻塞问题

同步意味着，在进行读写操作时，线程需要等待结果，还是相当于闲置。
异步意味着，在进行读写操作时，线程不必等待结果，而是将来由操作系统来通过回调方式由另外的线程来获得结果。

1.2、异步模型需要底层操作系统（Kernel）提供支持

Windows 系统通过 IOCP 实现了真正的异步 IO
Linux 系统异步 IO 在 2.6 版本引入，但其底层实现还是用多路复用模拟了异步 IO，性能没有优势

二、文件 AIO示例代码

示例代码

package com.example.nettytest.nio.day3;

import lombok.extern.slf4j.Slf4j;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.AsynchronousFileChannel;
import java.nio.channels.CompletionHandler;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
import static com.example.nettytest.nio.day1.ByteBufferUtil.debugAll;

@Slf4j
public class AioFileChannel 
    public static void main(String[] args) throws IOException 
        try (AsynchronousFileChannel channel = AsynchronousFileChannel.open(Paths.get("data.txt"), StandardOpenOption.READ)) 
            ByteBuffer buffer = ByteBuffer.allocate(16);
            log.debug("线程"+Thread.currentThread().getName()+":"+"read begin...");
            /**
             *  channel.read 异步操作
             *参数1 ByteBuffer
             *参数2 读取的起始位置
             *参数3 附件
             *参数4 回调对象 CompletionHandler
             * */
            channel.read(buffer, 0, buffer, new CompletionHandler<Integer, ByteBuffer>() 
                @Override //文件读取成功
                public void completed(Integer result, ByteBuffer attachment) 
                    log.debug("线程"+Thread.currentThread().getName()+"：read completed...", result);
                    attachment.flip();
                    debugAll(attachment);
                
                @Override //文件读取失败
                public void failed(Throwable exc, ByteBuffer attachment) 
                    exc.printStackTrace();
                
            );
            log.debug("线程"+Thread.currentThread().getName()+"：read end...");
         catch (IOException e) 
            e.printStackTrace();
        
        //主线程先接收控制台输出，如果没有输出即停止在此处
        System.in.read();

输出结果工具类

package com.example.nettytest.nio.day1;

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 main(String[] args) 
        ByteBuffer buffer = ByteBuffer.allocate(10);
        buffer.put(new byte[]97, 98, 99, 100);
        debugAll(buffer);
    

    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);

输出结果

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Netty—— AIO示例代码

目录

一、AIO 概述

1.1、AIO 用来解决数据复制阶段的阻塞问题

1.2、异步模型需要底层操作系统（Kernel）提供支持

二、文件 AIO示例代码