Java NIO三大組件與ByteBuffer深入理解及使用
1、三大組件
1.1 Channel & Buffer
channel 有一點(diǎn)類似于 stream，它就是讀寫數(shù)據(jù)的雙向通道，可以從 channel 將數(shù)據(jù)讀入 buffer，也可以將 buffer 的數(shù)據(jù)寫入 channel，而之前的 stream 要么是輸入，要么是輸出，channel 比 stream 更為底層
常見的 Channel 有
- FileChannel
- DatagramChannel
- SocketChannel
- ServerSocketChannel
buffer 則用來緩沖讀寫數(shù)據(jù)，常見的 buffer 有
- ByteBuffer
- MappedByteBuffer
- DirectByteBuffer
- HeapByteBuffer
- ShortBuffer
- IntBuffer
- LongBuffer
- FloatBuffer
- DoubleBuffer
- CharBuffer
1.2 Selector
selector 單從字面意思不好理解，需要結(jié)合服務(wù)器的設(shè)計(jì)演化來理解它的用途
多線程版設(shè)計(jì)
多線程版缺點(diǎn)
- 內(nèi)存占用高
- 線程上下文切換成本高
- 只適合連接數(shù)少的場(chǎng)景
線程池版設(shè)計(jì)
線程池版缺點(diǎn)
- 阻塞模式下，線程僅能處理一個(gè) socket 連接
- 僅適合短連接場(chǎng)景
selector 版設(shè)計(jì)
selector 的作用就是配合一個(gè)線程來管理多個(gè) channel，獲取這些 channel 上發(fā)生的事件，這些 channel 工作在非阻塞模式下，不會(huì)讓線程吊死在一個(gè) channel 上。適合連接數(shù)特別多，但流量低的場(chǎng)景（low traffic）
調(diào)用 selector 的 select() 會(huì)阻塞直到 channel 發(fā)生了讀寫就緒事件，這些事件發(fā)生，select 方法就會(huì)返回這些事件交給 thread 來處理
2、ByteBuffer
有一普通文本文件 data.txt，內(nèi)容為
1234567890abcd
使用 FileChannel 來讀取文件內(nèi)容
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();
}
}
}輸出
15:03:39.467 [main] DEBUG org.example.demo1.ChannelDemo1 - 讀到字節(jié)數(shù)：10
15:03:39.475 [main] DEBUG org.example.demo1.ChannelDemo1 - 實(shí)際字節(jié)1
15:03:39.475 [main] DEBUG org.example.demo1.ChannelDemo1 - 實(shí)際字節(jié)2
15:03:39.476 [main] DEBUG org.example.demo1.ChannelDemo1 - 實(shí)際字節(jié)3
15:03:39.476 [main] DEBUG org.example.demo1.ChannelDemo1 - 實(shí)際字節(jié)4
15:03:39.476 [main] DEBUG org.example.demo1.ChannelDemo1 - 實(shí)際字節(jié)5
15:03:39.476 [main] DEBUG org.example.demo1.ChannelDemo1 - 實(shí)際字節(jié)6
15:03:39.476 [main] DEBUG org.example.demo1.ChannelDemo1 - 實(shí)際字節(jié)7
15:03:39.476 [main] DEBUG org.example.demo1.ChannelDemo1 - 實(shí)際字節(jié)8
15:03:39.476 [main] DEBUG org.example.demo1.ChannelDemo1 - 實(shí)際字節(jié)9
15:03:39.476 [main] DEBUG org.example.demo1.ChannelDemo1 - 實(shí)際字節(jié)0
15:03:39.476 [main] DEBUG org.example.demo1.ChannelDemo1 - 讀到字節(jié)數(shù)：4
15:03:39.477 [main] DEBUG org.example.demo1.ChannelDemo1 - 實(shí)際字節(jié)a
15:03:39.477 [main] DEBUG org.example.demo1.ChannelDemo1 - 實(shí)際字節(jié)b
15:03:39.477 [main] DEBUG org.example.demo1.ChannelDemo1 - 實(shí)際字節(jié)c
15:03:39.477 [main] DEBUG org.example.demo1.ChannelDemo1 - 實(shí)際字節(jié)d
15:03:39.477 [main] DEBUG org.example.demo1.ChannelDemo1 - 讀到字節(jié)數(shù)：-1
2.1 ByteBuffer 正確使用姿勢(shì)
- 向 buffer 寫入數(shù)據(jù)，例如調(diào)用 channel.read(buffer)
- 調(diào)用 flip() 切換至讀模式
- 從 buffer 讀取數(shù)據(jù)，例如調(diào)用 buffer.get()
- 調(diào)用 clear() 或 compact() 切換至寫模式
- 重復(fù) 1~4 步驟
2.2 ByteBuffer 結(jié)構(gòu)
ByteBuffer 有以下重要屬性
- capacity
- position
- limit
一開始
寫模式下，position 是寫入位置，limit 等于容量，下圖表示寫入了 4 個(gè)字節(jié)后的狀態(tài)
flip 動(dòng)作發(fā)生后，position 切換為讀取位置，limit 切換為讀取限制
讀取 4 個(gè)字節(jié)后，狀態(tài)
clear 動(dòng)作發(fā)生后，狀態(tài)
compact 方法，是把未讀完的部分向前壓縮，然后切換至寫模式
調(diào)試工具類
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);
}
}測(cè)試如下：
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);
}
}運(yùn)行結(jié)果如下：
18:12:55.063 [main] DEBUG io.netty.util.internal.logging.InternalLoggerFactory - Using SLF4J as the default logging framework
+--------+-------------------- all ------------------------+----------------+
position: [1], limit: [10]
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 61 00 00 00 00 00 00 00 00 00 |a......... |
+--------+-------------------------------------------------+----------------+
+--------+-------------------- all ------------------------+----------------+
position: [4], limit: [10]
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 61 62 63 64 00 00 00 00 00 00 |abcd...... |
+--------+-------------------------------------------------+----------------+
+--------+-------------------- all ------------------------+----------------+
position: [5], limit: [10]
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 61 62 63 64 00 00 00 00 00 00 |abcd...... |
+--------+-------------------------------------------------+----------------+
+--------+-------------------- all ------------------------+----------------+
position: [1], limit: [5]
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 61 62 63 64 00 00 00 00 00 00 |abcd...... |
+--------+-------------------------------------------------+----------------+
+--------+-------------------- all ------------------------+----------------+
position: [4], limit: [10]
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 62 63 64 00 00 00 00 00 00 00 |bcd....... |
+--------+-------------------------------------------------+----------------+
Process finished with exit code 0
2.3 ByteBuffer 常見方法
分配空間
可以使用 allocate 方法為 ByteBuffer 分配空間，其它 buffer 類也有該方法
Bytebuffer buf = ByteBuffer.allocate(16);
例子：
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());
}
}運(yùn)行結(jié)果如下：
注意：
class java.nio.HeapByteBuffer -java 堆內(nèi)存，讀寫效率低，受到GC的影響 class java.nio.DirectByteBuffer -直接內(nèi)存，讀寫效率高（少一次拷貝），不會(huì)受GC影響，分配的效率低
向 buffer 寫入數(shù)據(jù)
有兩種辦法
- 調(diào)用 channel 的 read 方法
- 調(diào)用 buffer 自己的 put 方法
int readBytes = channel.read(buf);
和
buf.put((byte)127);
從 buffer 讀取數(shù)據(jù)
同樣有兩種辦法
- 調(diào)用channel的write方法
- 調(diào)用buffer自己的get方法
int writeBytes = channel.write(buf);
和
byte b = buf.get();
get 方法會(huì)讓 position 讀指針向后走，如果想重復(fù)讀取數(shù)據(jù)
可以調(diào)用 rewind 方法將 position 重新置為 0
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());
}
}調(diào)用結(jié)果：
+--------+-------------------- all ------------------------+----------------+
position: [4], limit: [4]
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 61 62 63 64 00 00 00 00 00 00 |abcd...... |
+--------+-------------------------------------------------+----------------+
===============================rewind================================
a
或者調(diào)用 get(int i) 方法獲取索引 i 的內(nèi)容，它不會(huì)移動(dòng)讀指針
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);
}
}調(diào)用結(jié)果：
mark 和 reset
mark 是在讀取時(shí)，做一個(gè)標(biāo)記，即使 position 改變，只要調(diào)用 reset 就能回到 mark 的位置
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());
}
}測(cè)試結(jié)果：
a
b
c
d
c
d
注意
rewind 和 flip 都會(huì)清除 mark 位置
字符串與ByteBuffer互轉(zhuǎn)
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);
}
}輸出：
+--------+-------------------- all ------------------------+----------------+
position: [5], limit: [16]
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 68 65 6c 6c 6f 00 00 00 00 00 00 00 00 00 00 00 |hello...........|
+--------+-------------------------------------------------+----------------+
hello
+--------+-------------------- all ------------------------+----------------+
position: [0], limit: [5]
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 68 65 6c 6c 6f |hello |
+--------+-------------------------------------------------+----------------+
+--------+-------------------- all ------------------------+----------------+
position: [0], limit: [5]
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 68 65 6c 6c 6f |hello |
+--------+-------------------------------------------------+----------------+
hello
Buffer的線程安全
Buffer是非線程安全的
2.4 Scattering Reads
分散讀取，有一個(gè)文本文件parts.txt
onetwothree
使用如下方式讀取，可以將數(shù)據(jù)填充至多個(gè) buffer
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();
}
}
}結(jié)果：
+--------+-------------------- all ------------------------+----------------+
position: [0], limit: [3]
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 6f 6e 65 |one |
+--------+-------------------------------------------------+----------------+
+--------+-------------------- all ------------------------+----------------+
position: [0], limit: [3]
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 74 77 6f |two |
+--------+-------------------------------------------------+----------------+
+--------+-------------------- all ------------------------+----------------+
position: [0], limit: [5]
+-------------------------------------------------+
| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 74 68 72 65 65 |three |
+--------+-------------------------------------------------+----------------+
2.5 Gathering Writes
使用如下方式寫入，可以將多個(gè) buffer 的數(shù)據(jù)填充至 channel
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){
}
}
}輸出結(jié)果：
2.6 黏包半包現(xiàn)象
網(wǎng)絡(luò)上有多條數(shù)據(jù)發(fā)送給服務(wù)端，數(shù)據(jù)之間使用 \n 進(jìn)行分隔 但由于某種原因這些數(shù)據(jù)在接收時(shí)，被進(jìn)行了重新組合，例如原始數(shù)據(jù)有3條為
- Hello,world\n
- I'm zhangsan\n
- How are you?\n
變成了下面的兩個(gè) byteBuffer (黏包，半包)
- Hello,world\nI'm zhangsan\nHo
- w are you?\n
現(xiàn)在要求你編寫程序，將錯(cuò)亂的數(shù)據(jù)恢復(fù)成原始的按 \n 分隔的數(shù)據(jù)
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();
}到此這篇關(guān)于Java NIO三大組件與ByteBuffer深入理解及使用的文章就介紹到這了,更多相關(guān)Java NIO三大組件內(nèi)容請(qǐng)搜索腳本之家以前的文章或繼續(xù)瀏覽下面的相關(guān)文章希望大家以后多多支持腳本之家！
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