2. ByteBuffer
2.1 基本使用
package com.sw.netty._01;
import lombok.extern.slf4j.Slf4j;
import java.io.IOException;
import java.io.InputStream;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.nio.channels.ReadableByteChannel;
@Slf4j
public class ByteBufferTest {
public static void main(String[] args) {
try (InputStream is = ByteBufferTest.class.getClassLoader().getResourceAsStream("ByteBufferTest.txt")) {
if (is == null) {
throw new IllegalArgumentException("resource not found: ByteBufferTest.txt");
}
try (ReadableByteChannel channel = Channels.newChannel(is)) {
// 准备缓冲区
ByteBuffer bf = ByteBuffer.allocate(10);
// 从 channel 读数据，写入 buffer
int len = channel.read(bf);
log.info("读取到的字节数：{}", len);
// 切换为读模式
bf.flip();
while (bf.hasRemaining()) {
byte b = bf.get();
log.info("读取到的字节：{}", (char) b);
}
// 切换为写模式
bf.clear();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
执行流程：
- 向 buffer 写入数据, channel.read(buffer)
- 调用 flip() 切换至读模式
- 从 buffer 读数据，buffer.get()
- 调用 clear() 或 compact() 切换至写模式
- 重复步骤 1 - 4
2.2 结构
buffer 包含的属性有：capacity、position、limit
开始：
写模式下，position 表示写入位置，limit 表示容量，写入4个字节
调用 flip 后，position 切换为读取位置， limit切换为读取限制
读取4个字节后的状态
调用 clear 后
调用 compact 方法，它的作用是把未读完的部分向前压缩，然后切换至写模式
ByteBufferReadWriteTest
public class ByteBufferReadWriteTest {
public static void main(String[] args) {
ByteBuffer bf = ByteBuffer.allocate(10);
bf.put((byte) 0x16);
debugAll(bf);
bf.put(new byte[]{0x17, 0x18, 0x19});
debugAll(bf);
bf.flip();
System.out.println(bf.get());
debugAll(bf);
bf.compact();
debugAll(bf);
bf.put(new byte[]{0x20, 0x21, 0x22});
debugAll(bf);
// +--------+-------------------- all ------------------------+----------------+
// position: [1], limit: [10]
// +-------------------------------------------------+
// | 0 1 2 3 4 5 6 7 8 9 a b c d e f |
// +--------+-------------------------------------------------+----------------+
// |00000000| 16 00 00 00 00 00 00 00 00 00 |.......... |
// +--------+-------------------------------------------------+----------------+
// +--------+-------------------- all ------------------------+----------------+
// position: [4], limit: [10]
// +-------------------------------------------------+
// | 0 1 2 3 4 5 6 7 8 9 a b c d e f |
// +--------+-------------------------------------------------+----------------+
// |00000000| 16 17 18 19 00 00 00 00 00 00 |.......... |
// +--------+-------------------------------------------------+----------------+
// 22
// +--------+-------------------- all ------------------------+----------------+
// position: [1], limit: [4]
// +-------------------------------------------------+
// | 0 1 2 3 4 5 6 7 8 9 a b c d e f |
// +--------+-------------------------------------------------+----------------+
// |00000000| 16 17 18 19 00 00 00 00 00 00 |.......... |
// +--------+-------------------------------------------------+----------------+
// +--------+-------------------- all ------------------------+----------------+
// position: [3], limit: [10]
// +-------------------------------------------------+
// | 0 1 2 3 4 5 6 7 8 9 a b c d e f |
// +--------+-------------------------------------------------+----------------+
// |00000000| 17 18 19 19 00 00 00 00 00 00 |.......... |
// +--------+-------------------------------------------------+----------------+
// +--------+-------------------- all ------------------------+----------------+
// position: [6], limit: [10]
// +-------------------------------------------------+
// | 0 1 2 3 4 5 6 7 8 9 a b c d e f |
// +--------+-------------------------------------------------+----------------+
// |00000000| 17 18 19 20 21 22 00 00 00 00 |... !".... |
// +--------+-------------------------------------------------+----------------+
}
}
2.3 常见方法
（1）分配空间
// 使用堆内存，会受 gc 的影响
ByteBuffer.allocate(10);
// 使用直接（物理）内存，读写效率高，但分配效率低
ByteBuffer.allocateDirect(10);（2）向 buffer 写入数据
调用 channel 的 read 方法
int len = channel.read(bf);调用 buffer 的 put 方法
bf.put((byte) 0x16)（3）从 buffer 读取数据
调用 channel 的 write 方法
int len = channel.write(bf);调用 buffer 的 get 方法
// get 方法会让 position 读指针向后走
// rewind 方法可以将 position 重新置为 0
// get(index) 方法获取指定索引下标的内容时，不会移动读指针
byte b = bf.get();ByteBufferReadTest
package com.sw.netty._01;
import java.nio.ByteBuffer;
import static utils.ByteBufferUtil.debugAll;
public class ByteBufferReadTest {
public static void main(String[] args) {
ByteBuffer bf = ByteBuffer.allocate(10);
bf.put(new byte[]{'a', 'b', 'c', 'd'});
bf.flip();
// 读全部
bf.get(new byte[4]);
debugAll(bf);
// 从头重新开始读取一个字节
bf.rewind();
System.out.println((char) bf.get());
// +--------+-------------------- 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...... |
// +--------+-------------------------------------------------+----------------+
// a
// mark 标记 position 位置，reset 将 position 位置重置到 mark 标记的位置
System.out.println((char) bf.get()); // b
bf.mark();
System.out.println((char) bf.get()); // c
System.out.println((char) bf.get()); // d
bf.reset();
System.out.println((char) bf.get()); // c
// get(index) 不会改变读索引的位置
System.out.println((char) bf.get(3));
debugAll(bf);
// d
// +--------+-------------------- all ------------------------+----------------+
// position: [1], 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...... |
// +--------+-------------------------------------------------+----------------+
}
}
（4）字符串与 ByteBuffer 互转
package com.sw.netty._01;
import java.nio.ByteBuffer;
import java.nio.charset.StandardCharsets;
import static utils.ByteBufferUtil.debugAll;
public class ByteBuffer2StringTest {
public static void main(String[] args) {
ByteBuffer bf = ByteBuffer.allocate(10);
// 字符串转 ByteBuffer
// 1. 字符串 getBytes()
bf.put("sxc".getBytes());
debugAll(bf);
// +--------+-------------------- all ------------------------+----------------+
// position: [3], limit: [16]
// +-------------------------------------------------+
// | 0 1 2 3 4 5 6 7 8 9 a b c d e f |
// +--------+-------------------------------------------------+----------------+
// |00000000| 73 78 63 00 00 00 00 00 00 00 00 00 00 00 00 00 |sxc.............|
// +--------+-------------------------------------------------+----------------+
// 2. Charset encode之后自动切换为读模式
ByteBuffer bf1 = StandardCharsets.UTF_8.encode("sxc");
debugAll(bf1);
// +--------+-------------------- all ------------------------+----------------+
// position: [0], limit: [3]
// +-------------------------------------------------+
// | 0 1 2 3 4 5 6 7 8 9 a b c d e f |
// +--------+-------------------------------------------------+----------------+
// |00000000| 73 78 63 |sxc |
// +--------+-------------------------------------------------+----------------+
// 3. wrap 同理方法2，自动切换为读模式
ByteBuffer bf2 = ByteBuffer.wrap("sxc".getBytes());
debugAll(bf2);
// +--------+-------------------- all ------------------------+----------------+
// position: [0], limit: [3]
// +-------------------------------------------------+
// | 0 1 2 3 4 5 6 7 8 9 a b c d e f |
// +--------+-------------------------------------------------+----------------+
// |00000000| 73 78 63 |sxc |
// +--------+-------------------------------------------------+----------------+
// ByteBuffer 转字符串
bf.flip();
System.out.println(StandardCharsets.UTF_8.decode(bf)); //sxc
// Charset、wrap 方法生成的 ByteBuffer 对象不需要再手动显示切换为读模式
System.out.println(StandardCharsets.UTF_8.decode(bf1)); //sxc
System.out.println(StandardCharsets.UTF_8.decode(bf2)); //sxc
}
}
2.4 Scattering Reads 分散读
ScatteringReadsTest
package com.sw.netty._01;
import java.net.URL;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.file.Paths;
import static utils.ByteBufferUtil.debugAll;
public class ScatteringReadsTest {
public static void main(String[] args) {
URL resource = ScatteringReadsTest.class.getClassLoader().getResource("ScatteringReadsTest.txt");
if (resource == null) {
throw new IllegalArgumentException("resource not found: ScatteringReadsTest.txt");
}
try (FileChannel channel = FileChannel.open(Paths.get(resource.toURI()))) {
ByteBuffer bf1 = ByteBuffer.allocate(3);
ByteBuffer bf2 = ByteBuffer.allocate(3);
ByteBuffer bf3 = ByteBuffer.allocate(3);
channel.read(new ByteBuffer[]{bf1, bf2, bf3});
bf1.flip();
bf2.flip();
bf3.flip();
debugAll(bf1);
debugAll(bf2);
debugAll(bf3);
// +--------+-------------------- all ------------------------+----------------+
// position: [0], limit: [3]
// +-------------------------------------------------+
// | 0 1 2 3 4 5 6 7 8 9 a b c d e f |
// +--------+-------------------------------------------------+----------------+
// |00000000| 31 32 33 |123 |
// +--------+-------------------------------------------------+----------------+
// +--------+-------------------- all ------------------------+----------------+
// position: [0], limit: [3]
// +-------------------------------------------------+
// | 0 1 2 3 4 5 6 7 8 9 a b c d e f |
// +--------+-------------------------------------------------+----------------+
// |00000000| 34 35 36 |456 |
// +--------+-------------------------------------------------+----------------+
// +--------+-------------------- all ------------------------+----------------+
// position: [0], limit: [3]
// +-------------------------------------------------+
// | 0 1 2 3 4 5 6 7 8 9 a b c d e f |
// +--------+-------------------------------------------------+----------------+
// |00000000| 37 38 39 |789 |
// +--------+-------------------------------------------------+----------------+
} catch (Exception e) {
e.printStackTrace();
}
}
}
2.5 GatheringWrites 集中写
GatheringWritesTest
package com.sw.netty._01;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.StandardCharsets;
public class GatheringWritesTest {
public static void main(String[] args) {
ByteBuffer bf1 = StandardCharsets.UTF_8.encode("sun");
ByteBuffer bf2 = StandardCharsets.UTF_8.encode("xiao");
ByteBuffer bf3 = StandardCharsets.UTF_8.encode("chuan");
try (FileChannel channel = new RandomAccessFile("GatheringWritesTest.txt", "rw").getChannel()) {
channel.write(new ByteBuffer[]{bf1, bf2, bf3});
} catch (IOException e) {
e.printStackTrace();
}
}
}
2.6 黏包、半包
ByteBufferExamTest
package com.sw.netty._01;
import java.nio.ByteBuffer;
import static utils.ByteBufferUtil.debugAll;
public class ByteBufferExamTest {
public static void main(String[] args) {
/**
* 例：通过网络发送给服务器的多条数据如下：
* Yao Shui Ge,\n
* Jin Se Wei Ye Na,\n
* Zhi Bo Jian.
* 由于各种原因，变成了如下的形式（黏包、半包）
* Yao Shui Ge,\nJin S
* e Wei Ye Na,\nZ
* hi Bo Jian.
* 现要求将黏包、半包的数据恢复为正确的按 \n 分隔的数据
*/
ByteBuffer originBf = ByteBuffer.allocate(45);
originBf.put("Yao Shui Ge,\nJin S".getBytes());
split(originBf);
originBf.put("e Wei Ye Na,\nZ".getBytes());
split(originBf);
originBf.put("hi Bo Jian.\n".getBytes());
split(originBf);
}
private static void split(ByteBuffer source) {
source.flip();
for (int i = 0; i < source.limit(); i++) {
if ('\n' == source.get(i)) {
int length = i + 1 - source.position();
ByteBuffer target = ByteBuffer.allocate(length);
// 从 source 读，向 target 写
for (int j = 0; j < length; j++) {
target.put(source.get());
}
debugAll(target);
}
}
// 此处不使用 clear，需使用 compact 将剩余未读的部分向前移动
source.compact();
}
// +--------+-------------------- all ------------------------+----------------+
// position: [13], limit: [13]
// +-------------------------------------------------+
// | 0 1 2 3 4 5 6 7 8 9 a b c d e f |
// +--------+-------------------------------------------------+----------------+
// |00000000| 59 61 6f 20 53 68 75 69 20 47 65 2c 0a |Yao Shui Ge,. |
// +--------+-------------------------------------------------+----------------+
// +--------+-------------------- all ------------------------+----------------+
// position: [18], limit: [18]
// +-------------------------------------------------+
// | 0 1 2 3 4 5 6 7 8 9 a b c d e f |
// +--------+-------------------------------------------------+----------------+
// |00000000| 4a 69 6e 20 53 65 20 57 65 69 20 59 65 20 4e 61 |Jin Se Wei Ye Na|
// |00000010| 2c 0a |,. |
// +--------+-------------------------------------------------+----------------+
// +--------+-------------------- all ------------------------+----------------+
// position: [13], limit: [13]
// +-------------------------------------------------+
// | 0 1 2 3 4 5 6 7 8 9 a b c d e f |
// +--------+-------------------------------------------------+----------------+
// |00000000| 5a 68 69 20 42 6f 20 4a 69 61 6e 2e 0a |Zhi Bo Jian.. |
// +--------+-------------------------------------------------+----------------+
}
评论 (0)