结构
image.png
小demo
package com.cow.cowboy.netty;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.ByteBufAllocator;
public class ByteBufTest {
public static void main(String[] args) {
ByteBuf buffer = ByteBufAllocator.DEFAULT.buffer(9, 100);
print("allocate ByteBuf(9, 100)", buffer);
// write 方法改变写指针，写完之后写指针未到 capacity 的时候，buffer 仍然可写
buffer.writeBytes(new byte[]{1, 2, 3, 4});
print("writeBytes(1,2,3,4)", buffer);
// write 方法改变写指针，写完之后写指针未到 capacity 的时候，buffer 仍然可写, 写完 int 类型之后，写指针增加4
buffer.writeInt(12);
print("writeInt(12)", buffer);
// write 方法改变写指针, 写完之后写指针等于 capacity 的时候，buffer 不可写
buffer.writeBytes(new byte[]{5});
print("writeBytes(5)", buffer);
// write 方法改变写指针，写的时候发现 buffer 不可写则开始扩容，扩容之后 capacity 随即改变
buffer.writeBytes(new byte[]{6});
print("writeBytes(6)", buffer);
// get 方法不改变读写指针
System.out.println("getByte(3) return: " + buffer.getByte(3));
System.out.println("getShort(3) return: " + buffer.getShort(3));
System.out.println("getInt(3) return: " + buffer.getInt(3));
print("getByte()", buffer);
// set 方法不改变读写指针
buffer.setByte(buffer.readableBytes() + 1, 0);
print("setByte()", buffer);
// read 方法改变读指针
byte[] dst = new byte[buffer.readableBytes()];
buffer.readBytes(dst);
print("readBytes(" + dst.length + ")", buffer);
}
private static void print(String action, ByteBuf buffer) {
System.out.println("after ===========" + action + "============");
System.out.println("capacity(): " + buffer.capacity());
System.out.println("maxCapacity(): " + buffer.maxCapacity());
System.out.println("readerIndex(): " + buffer.readerIndex());
System.out.println("readableBytes(): " + buffer.readableBytes());
System.out.println("isReadable(): " + buffer.isReadable());
System.out.println("writerIndex(): " + buffer.writerIndex());
System.out.println("writableBytes(): " + buffer.writableBytes());
System.out.println("isWritable(): " + buffer.isWritable());
System.out.println("maxWritableBytes(): " + buffer.maxWritableBytes());
System.out.println();
}
}
输出结果：
after ===========allocate ByteBuf(9, 100)============
capacity(): 9
maxCapacity(): 100
readerIndex(): 0
readableBytes(): 0
isReadable(): false
writerIndex(): 0
writableBytes(): 9
isWritable(): true
maxWritableBytes(): 100
after ===========writeBytes(1,2,3,4)============
capacity(): 9
maxCapacity(): 100
readerIndex(): 0
readableBytes(): 4
isReadable(): true
writerIndex(): 4
writableBytes(): 5
isWritable(): true
maxWritableBytes(): 96
after ===========writeInt(12)============
capacity(): 9
maxCapacity(): 100
readerIndex(): 0
readableBytes(): 8
isReadable(): true
writerIndex(): 8
writableBytes(): 1
isWritable(): true
maxWritableBytes(): 92
after ===========writeBytes(5)============
capacity(): 9
maxCapacity(): 100
readerIndex(): 0
readableBytes(): 9
isReadable(): true
writerIndex(): 9
writableBytes(): 0
isWritable(): false
maxWritableBytes(): 91
after ===========writeBytes(6)============
capacity(): 64
maxCapacity(): 100
readerIndex(): 0
readableBytes(): 10
isReadable(): true
writerIndex(): 10
writableBytes(): 54
isWritable(): true
maxWritableBytes(): 90
getByte(3) return: 4
getShort(3) return: 1024
getInt(3) return: 67108864
after ===========getByte()============
capacity(): 64
maxCapacity(): 100
readerIndex(): 0
readableBytes(): 10
isReadable(): true
writerIndex(): 10
writableBytes(): 54
isWritable(): true
maxWritableBytes(): 90
after ===========setByte()============
capacity(): 64
maxCapacity(): 100
readerIndex(): 0
readableBytes(): 10
isReadable(): true
writerIndex(): 10
writableBytes(): 54
isWritable(): true
maxWritableBytes(): 90
after ===========readBytes(10)============
capacity(): 64
maxCapacity(): 100
readerIndex(): 10
readableBytes(): 0
isReadable(): false
writerIndex(): 10
writableBytes(): 54
isWritable(): true
maxWritableBytes(): 90
来源掘金小册