1.第一步先创建一个项目添加一下依赖
1.1 利用bytebuffer写一下案列
java
package com.netty.demo;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
public class TestByteBuffer {
public static void main(String[] args) {
// FileChannel
// 1 输入输出流 2 RandomAccessFile
try {
FileChannel channel = new FileInputStream("data.txt").getChannel();
// 准备缓冲区,设置缓冲区大小
ByteBuffer buffer = ByteBuffer.allocate(10);
while (true){
// 从channel读取数据，写入buffer
int read = channel.read(buffer);
if (read == -1){ // 没有内容了
break;
}
// 打印buffer内容
buffer.flip(); // 切换只读模式
// 然后判定buffer是否读取完毕
while (buffer.hasRemaining()){
byte b = buffer.get();
System.out.println((char) b);
}
buffer.clear();// 切换成写模式
}
} catch (Exception e) {
throw new RuntimeException(e);
}
}
}
这句话的意思大概是如果是-1代表没有了。这种可能分批读取。
1.2 bytebuffer内部结构
ByteBuffer有以下重要属性
capacity
position
limit
写模式下 position是写入模式，limit等于容量，下图表示写入4个字节后的状态
flip动作发生后，position切换为读取位置，limit切换为读取限制
读取4个字节状态
'
clear发生后
compact方法，是把未读玩的部分向前压缩，然后切换只写模式
1.3 bytebuffer演示方法1
这是一个工具类
java
package com.netty.demo;
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);
}
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);
}
}根据以下代码可以看出position的limit的指针，以及大小，这是写入
接下来是读，如果在读取之前未使用flip，position的指针是0所以读不到数据
直接切换这是最终的数据postion指针到1，然后limit最大是4
compact 压缩未读取的数据
然后切换到写模式
1.4 bytebuffer 演示方法2
1.5 bytebuffer演示方法3
java
package com.netty.demo;
import java.nio.ByteBuffer;
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 从头开始读取
// buffer.get(new byte[4]);
// ByteBufferUtil.debugAll(buffer);
// buffer.rewind();
// System.out.println((char) buffer.get());
// mark & reset
// mark 做一个标记，记录position的位置，reset是将position重置到mark的位置
// System.out.println((char) buffer.get());
// System.out.println((char) buffer.get());
// // mark 做一个标记
// buffer.mark();
// // 然后接着读
// System.out.println((char) buffer.get());
// System.out.println((char) buffer.get());
// // 然后拿到那个标记
// buffer.reset();
// System.out.println((char) buffer.get());
// System.out.println((char) buffer.get());
// get(i) 类似循环里面的i下标
System.out.println((char) buffer.get(3));
ByteBufferUtil.debugAll(buffer);
}
}1.6 bytebuffer演示方法4
string类型转换为bytebuffer
1.7 bytebuffer分散度集中写
分散度
集中写
