Netty—— AIO示例代码

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