Netty——ByteBuffer 的分散读（Scattering Reads）、集中写（Gathering Writes）示例

转x33g5p2x  于2022-07-26 转载在 其他  
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一、ByteBuffer 的分散读（Scattering Reads）的示例

  • 工具类
  1. package com.example.nettytest.nio.day1;
  3. import io.netty.util.internal.StringUtil;
  5. import java.nio.ByteBuffer;
  7. import static io.netty.util.internal.MathUtil.isOutOfBounds;
  8. import static io.netty.util.internal.StringUtil.NEWLINE;
  10. public class ByteBufferUtil {
  11.     private static final char[] BYTE2CHAR = new char[256];
  12.     private static final char[] HEXDUMP_TABLE = new char[256 * 4];
  13.     private static final String[] HEXPADDING = new String[16];
  14.     private static final String[] HEXDUMP_ROWPREFIXES = new String[65536 >>> 4];
  15.     private static final String[] BYTE2HEX = new String[256];
  16.     private static final String[] BYTEPADDING = new String[16];
  18.     static {
  19.         final char[] DIGITS = "0123456789abcdef".toCharArray();
  20.         for (int i = 0; i < 256; i++) {
  21.             HEXDUMP_TABLE[i << 1] = DIGITS[i >>> 4 & 0x0F];
  22.             HEXDUMP_TABLE[(i << 1) + 1] = DIGITS[i & 0x0F];
  23.         }
  25.         int i;
  27.         // Generate the lookup table for hex dump paddings
  28.         for (i = 0; i < HEXPADDING.length; i++) {
  29.             int padding = HEXPADDING.length - i;
  30.             StringBuilder buf = new StringBuilder(padding * 3);
  31.             for (int j = 0; j < padding; j++) {
  32.                 buf.append("   ");
  33.             }
  34.             HEXPADDING[i] = buf.toString();
  35.         }
  37.         // Generate the lookup table for the start-offset header in each row (up to 64KiB).
  38.         for (i = 0; i < HEXDUMP_ROWPREFIXES.length; i++) {
  39.             StringBuilder buf = new StringBuilder(12);
  40.             buf.append(NEWLINE);
  41.             buf.append(Long.toHexString(i << 4 & 0xFFFFFFFFL | 0x100000000L));
  42.             buf.setCharAt(buf.length() - 9, '|');
  43.             buf.append('|');
  44.             HEXDUMP_ROWPREFIXES[i] = buf.toString();
  45.         }
  47.         // Generate the lookup table for byte-to-hex-dump conversion
  48.         for (i = 0; i < BYTE2HEX.length; i++) {
  49.             BYTE2HEX[i] = ' ' + StringUtil.byteToHexStringPadded(i);
  50.         }
  52.         // Generate the lookup table for byte dump paddings
  53.         for (i = 0; i < BYTEPADDING.length; i++) {
  54.             int padding = BYTEPADDING.length - i;
  55.             StringBuilder buf = new StringBuilder(padding);
  56.             for (int j = 0; j < padding; j++) {
  57.                 buf.append(' ');
  58.             }
  59.             BYTEPADDING[i] = buf.toString();
  60.         }
  62.         // Generate the lookup table for byte-to-char conversion
  63.         for (i = 0; i < BYTE2CHAR.length; i++) {
  64.             if (i <= 0x1f || i >= 0x7f) {
  65.                 BYTE2CHAR[i] = '.';
  66.             } else {
  67.                 BYTE2CHAR[i] = (char) i;
  68.             }
  69.         }
  70.     }
  72.     /**
  73.      * 打印所有内容
  74.      * @param buffer
  75.      */
  76.     public static void debugAll(ByteBuffer buffer) {
  77.         int oldlimit = buffer.limit();
  78.         buffer.limit(buffer.capacity());
  79.         StringBuilder origin = new StringBuilder(256);
  80.         appendPrettyHexDump(origin, buffer, 0, buffer.capacity());
  81.         System.out.println("+--------+-------------------- all ------------------------+----------------+");
  82.         System.out.printf("position: [%d], limit: [%d]\n", buffer.position(), oldlimit);
  83.         System.out.println(origin);
  84.         buffer.limit(oldlimit);
  85.     }
  87.     /**
  88.      * 打印可读取内容
  89.      * @param buffer
  90.      */
  91.     public static void debugRead(ByteBuffer buffer) {
  92.         StringBuilder builder = new StringBuilder(256);
  93.         appendPrettyHexDump(builder, buffer, buffer.position(), buffer.limit() - buffer.position());
  94.         System.out.println("+--------+-------------------- read -----------------------+----------------+");
  95.         System.out.printf("position: [%d], limit: [%d]\n", buffer.position(), buffer.limit());
  96.         System.out.println(builder);
  97.     }
  99.     public static void main(String[] args) {
  100.         ByteBuffer buffer = ByteBuffer.allocate(10);
  101.         buffer.put(new byte[]{97, 98, 99, 100});
  102.         debugAll(buffer);
  103.     }
  105.     private static void appendPrettyHexDump(StringBuilder dump, ByteBuffer buf, int offset, int length) {
  106.         if (isOutOfBounds(offset, length, buf.capacity())) {
  107.             throw new IndexOutOfBoundsException(
  108.                     "expected: " + "0 <= offset(" + offset + ") <= offset + length(" + length
  109.                             + ") <= " + "buf.capacity(" + buf.capacity() + ')');
  110.         }
  111.         if (length == 0) {
  112.             return;
  113.         }
  114.         dump.append(
  115.                 "         +-------------------------------------------------+" +
  116.                         NEWLINE + "         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |" +
  117.                         NEWLINE + "+--------+-------------------------------------------------+----------------+");
  119.         final int startIndex = offset;
  120.         final int fullRows = length >>> 4;
  121.         final int remainder = length & 0xF;
  123.         // Dump the rows which have 16 bytes.
  124.         for (int row = 0; row < fullRows; row++) {
  125.             int rowStartIndex = (row << 4) + startIndex;
  127.             // Per-row prefix.
  128.             appendHexDumpRowPrefix(dump, row, rowStartIndex);
  130.             // Hex dump
  131.             int rowEndIndex = rowStartIndex + 16;
  132.             for (int j = rowStartIndex; j < rowEndIndex; j++) {
  133.                 dump.append(BYTE2HEX[getUnsignedByte(buf, j)]);
  134.             }
  135.             dump.append(" |");
  137.             // ASCII dump
  138.             for (int j = rowStartIndex; j < rowEndIndex; j++) {
  139.                 dump.append(BYTE2CHAR[getUnsignedByte(buf, j)]);
  140.             }
  141.             dump.append('|');
  142.         }
  144.         // Dump the last row which has less than 16 bytes.
  145.         if (remainder != 0) {
  146.             int rowStartIndex = (fullRows << 4) + startIndex;
  147.             appendHexDumpRowPrefix(dump, fullRows, rowStartIndex);
  149.             // Hex dump
  150.             int rowEndIndex = rowStartIndex + remainder;
  151.             for (int j = rowStartIndex; j < rowEndIndex; j++) {
  152.                 dump.append(BYTE2HEX[getUnsignedByte(buf, j)]);
  153.             }
  154.             dump.append(HEXPADDING[remainder]);
  155.             dump.append(" |");
  157.             // Ascii dump
  158.             for (int j = rowStartIndex; j < rowEndIndex; j++) {
  159.                 dump.append(BYTE2CHAR[getUnsignedByte(buf, j)]);
  160.             }
  161.             dump.append(BYTEPADDING[remainder]);
  162.             dump.append('|');
  163.         }
  165.         dump.append(NEWLINE +
  166.                 "+--------+-------------------------------------------------+----------------+");
  167.     }
  169.     private static void appendHexDumpRowPrefix(StringBuilder dump, int row, int rowStartIndex) {
  170.         if (row < HEXDUMP_ROWPREFIXES.length) {
  171.             dump.append(HEXDUMP_ROWPREFIXES[row]);
  172.         } else {
  173.             dump.append(NEWLINE);
  174.             dump.append(Long.toHexString(rowStartIndex & 0xFFFFFFFFL | 0x100000000L));
  175.             dump.setCharAt(dump.length() - 9, '|');
  176.             dump.append('|');
  177.         }
  178.     }
  180.     public static short getUnsignedByte(ByteBuffer buffer, int index) {
  181.         return (short) (buffer.get(index) & 0xFF);
  182.     }
  183. }
  • readData.txt文件内容

  • 示例代码
  1. package com.example.nettytest.nio.day1;
  3. import java.io.IOException;
  4. import java.io.RandomAccessFile;
  5. import java.nio.ByteBuffer;
  6. import java.nio.channels.FileChannel;
  8. import static com.example.nettytest.nio.day1.ByteBufferUtil.debugAll;
  10. /**
  11.  * @description: 分散读示例
  12.  * @author: xz
  13.  * @create: 2022-07-24 20:54
  14.  */
  15. public class TestScatteringReads {
  16.     public static void main(String[] args) {
  17.         try (FileChannel channel = new RandomAccessFile("readData.txt", "r").getChannel()) {
  18.             ByteBuffer b1 = ByteBuffer.allocate(3);
  19.             ByteBuffer b2 = ByteBuffer.allocate(3);
  20.             ByteBuffer b3 = ByteBuffer.allocate(5);
  21.             channel.read(new ByteBuffer[]{b1, b2, b3});
  22.             b1.flip();
  23.             b2.flip();
  24.             b3.flip();
  25.             debugAll(b1);
  26.             debugAll(b2);
  27.             debugAll(b3);
  28.         } catch (IOException e) {
  29.         }
  30.     }
  31. }
  • 输出结果

二、ByteBuffer 的集中写示例（Gathering Writes）的示例

  • writeData.txt文件中内容为空

  • 示例代码
  1. package com.example.nettytest.nio.day1;
  3. import java.io.IOException;
  4. import java.io.RandomAccessFile;
  5. import java.nio.ByteBuffer;
  6. import java.nio.channels.FileChannel;
  7. import java.nio.charset.StandardCharsets;
  9. /**
  10.  * @description: 集中写示例
  11.  * @author: xz
  12.  * @create: 2022-07-24 21:07
  13.  */
  14. public class TestGatheringWrites {
  15.     public static void main(String[] args) {
  16.         ByteBuffer b1 = StandardCharsets.UTF_8.encode("hello");
  17.         ByteBuffer b2 = StandardCharsets.UTF_8.encode("world");
  18.         ByteBuffer b3 = StandardCharsets.UTF_8.encode("你好");
  20.         try (FileChannel channel = new RandomAccessFile("writeData.txt", "rw").getChannel()) {
  21.             channel.write(new ByteBuffer[]{b1, b2, b3});
  22.         } catch (IOException e) {
  23.         }
  24.     }
  25. }
  • 输出结果

版权说明 : 本文为转载文章, 版权归原作者所有 版权申明

原文链接 : https://wwwxz.blog.csdn.net/article/details/125964360

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