java | bytebuffer 方法演示

bytebuffer 方法演示。

引入自写的方法类。

下载 JAVA 文件

netty 包

<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-all</artifactId>
    <version>4.1.86.Final</version>
</dependency>

position 位置

这个要结合 java | bytebuffer 用法 | bytebuffer 内部结构

package com.redisc;

import lombok.extern.slf4j.Slf4j;

import java.nio.ByteBuffer;

import static com.redisc.ByteBufferUtil.debugAll;

@Slf4j(topic = "c.Test")
public class Run {

    public static void main(String[] args) {
        ByteBuffer buffer = ByteBuffer.allocate(10);

        buffer.put((byte) 0x61); // 'a'
        debugAll(buffer);
        buffer.put(new byte[]{0x62, 0x63}); // 'abc'
        debugAll(buffer);
        buffer.flip(); // position 指向 0
        System.out.println(buffer.get()); // 输出 a
        debugAll(buffer);
        buffer.compact(); // 把 a 去除，后面的补上来 position 指向 2
        debugAll(buffer);
        buffer.put(new byte[]{0x65}); // 'bce'
        debugAll(buffer);
    }
}

输出

+--------+-------------------- 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: [3], limit: [10]
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 61 62 63 00 00 00 00 00 00 00                   |abc.......      |
+--------+-------------------------------------------------+----------------+
97
+--------+-------------------- all ------------------------+----------------+
position: [1], limit: [3]
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 61 62 63 00 00 00 00 00 00 00                   |abc.......      |
+--------+-------------------------------------------------+----------------+
+--------+-------------------- all ------------------------+----------------+
position: [2], limit: [10]
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 62 63 63 00 00 00 00 00 00 00                   |bcc.......      |
+--------+-------------------------------------------------+----------------+
+--------+-------------------- all ------------------------+----------------+
position: [3], limit: [10]
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 62 63 65 00 00 00 00 00 00 00                   |bce.......      |
+--------+-------------------------------------------------+----------------+

分配内存

package com.redisc;

import lombok.extern.slf4j.Slf4j;

import java.nio.ByteBuffer;

@Slf4j(topic = "c.Test")
public class Run {

    public static void main(String[] args) {
        System.out.println(ByteBuffer.allocate(16).getClass());
        System.out.println(ByteBuffer.allocateDirect(16).getClass());
    }
}

输出

class java.nio.HeapByteBuffer --java 堆内存，读写效率低，垃圾可以回收
class java.nio.DirectByteBuffer -- 直接内存，读写效率高，垃圾不回收，分配的效率低

读写

写入

• 调用 channel 的 read 方法
  • int readBytes = channel.read(buf);
• 调用 buffer 自己的 put 方法
  • buf.put((byte)127);

读取

• 调用 channel 的 write 方法
  • int writeBytes = channel.write(buf);
• 调用 buffer 自己的 get 方法
  • byte b = buf.get();

package com.redisc;

import lombok.extern.slf4j.Slf4j;

import java.nio.ByteBuffer;

@Slf4j(topic = "c.Test")
public class Run {

    public static void main(String[] args) {
        ByteBuffer buffer = ByteBuffer.allocate(10);
        buffer.put(new byte[]{'a','b','c','d'});
        buffer.flip();

        //从头读
        buffer.get(new byte[4]); // 会移动 position abcd
        buffer.rewind(); //再次把 position 指向 0，又可以重新读取了
        buffer.get(); // a position 指向 1
        buffer.mark(); // 做标记，记录一下 position 位置，mark = 1
        buffer.get(); // b position 指向 2
        buffer.reset(); // 将 position 重制到 mark 位置 position = 1
        System.out.println((char)buffer.get()); // b
        buffer.get(3); // d 但是 position 不会变 get(i) 不改变读索引的位置


    }
}

字符串与 bytebuffer 互转

package com.redisc;

import lombok.extern.slf4j.Slf4j;

import java.nio.ByteBuffer;
import java.nio.charset.StandardCharsets;

@Slf4j(topic = "c.Test")
public class Run {

    public static void main(String[] args) {
        // 字符串转化为 ByteBuffer
        ByteBuffer buffer = ByteBuffer.allocate(16);
        buffer.put("hello".getBytes()); // 还是写模式 position = 5

        // Charset
        ByteBuffer byteBuffer = StandardCharsets.UTF_8.encode("hello"); // 执行完，已经是读模式了 position = 0

        // wrap
        ByteBuffer byteBuffer1 = ByteBuffer.wrap("hello".getBytes()); // 执行完直接切换到读模式

        // bytebuffer 转为 string
        String str1 = StandardCharsets.UTF_8.decode(byteBuffer1).toString(); // 这个需要切换到读模式才能使用

    }
}