java | bytebuf 组成、写入、读取

bytebuf 的结构。

bytebuff 的结构如下 java | bytebuffer 用法

bytebuf 有 4 个部分组成

package com.redisc;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.ByteBufAllocator;
import lombok.extern.slf4j.Slf4j;

import java.io.IOException;

import static io.netty.buffer.ByteBufUtil.appendPrettyHexDump;
import static io.netty.util.internal.StringUtil.NEWLINE;


@Slf4j
public class Run {

public static void main(String[] args) throws IOException {
        ByteBuf byteBuf = ByteBufAllocator.DEFAULT.directBuffer(); // 默认长度 256
        byteBuf.writeBytes(new byte[]{1,2,3,4});
        log(byteBuf);
        byteBuf.writeInt(5); // 4 个字节
        log(byteBuf);
    }

private static void log(ByteBuf buffer){
        int length=buffer.readableBytes();
        int rows=length/16+(length%15==0?0:1)+4;
        StringBuilder buf=new StringBuilder(rows*80*2)
                .append("read index:").append(buffer.readerIndex())
                .append(" write index:").append(buffer.writerIndex())
                .append(" capacity:").append(buffer.capacity())
                .append(NEWLINE);
        appendPrettyHexDump(buf,buffer);
        System.out.println(buf.toString());
    }
}

read index:0 write index:4 capacity:256
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 01 02 03 04                                     |....            |
+--------+-------------------------------------------------+----------------+
read index:0 write index:8 capacity:256
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 01 02 03 04 00 00 00 05                         |........        |
+--------+-------------------------------------------------+----------------+

还有一类方法，是 set 开头的，可以写入数据，但是，不会改变指针位置。

• 写入数据的大小未超过 512，则选择下一个 16 的整数倍，例如写入后大小为 12，则扩容后容量为 16
• 写入后数据大小超过 512，则下一个为 2^n，例如，写入后大小为 513，则扩容为 2^10 = 1024 「2^9 = 512」
• 扩容不能超过 max capacity，否则会报错

读过的部分就是废弃的部分，再读只能读未读取的部分。

bytebuf.readByte() 读取一个字节

具体的代码如下

package com.redisc;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.ByteBufAllocator;
import lombok.extern.slf4j.Slf4j;

import java.io.IOException;

import static io.netty.buffer.ByteBufUtil.appendPrettyHexDump;
import static io.netty.util.internal.StringUtil.NEWLINE;


@Slf4j
public class Run {

public static void main(String[] args) throws IOException {
        ByteBuf byteBuf = ByteBufAllocator.DEFAULT.directBuffer(); // 默认长度 256
        byteBuf.writeBytes(new byte[]{1,2,3,4});
        log(byteBuf);
        byteBuf.writeInt(5); // 4 个字节
        log(byteBuf);

System.out.println(byteBuf.readByte());
        System.out.println(byteBuf.readByte());
        System.out.println(byteBuf.readByte());
        System.out.println(byteBuf.readByte());
        log(byteBuf);

byteBuf.markReaderIndex(); // 标记一个指针
        System.out.println(byteBuf.readInt());
        log(byteBuf);

byteBuf.resetReaderIndex(); //将读指针返回 mark
        log(byteBuf);
    }

private static void log(ByteBuf buffer){
        int length=buffer.readableBytes();
        int rows=length/16+(length%15==0?0:1)+4;
        StringBuilder buf=new StringBuilder(rows*80*2)
                .append("read index:").append(buffer.readerIndex())
                .append(" write index:").append(buffer.writerIndex())
                .append(" capacity:").append(buffer.capacity())
                .append(NEWLINE);
        appendPrettyHexDump(buf,buffer);
        System.out.println(buf.toString());
    }
}

read index:0 write index:4 capacity:256
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 01 02 03 04                                     |....            |
+--------+-------------------------------------------------+----------------+
read index:0 write index:8 capacity:256
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 01 02 03 04 00 00 00 05                         |........        |
+--------+-------------------------------------------------+----------------+
1
2
3
4
read index:4 write index:8 capacity:256
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 00 00 00 05                                     |....            |
+--------+-------------------------------------------------+----------------+
5
read index:8 write index:8 capacity:256

read index:4 write index:8 capacity:256
         +-------------------------------------------------+
         |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 00 00 00 05                                     |....            |
+--------+-------------------------------------------------+----------------+

还有一部分方法是 get 开头的，这个不改变指针。