Netty使用记录-ByteBuf.duplicate和copy的区别

ByteBuf.copy是拷贝一个新的对象，修改新对象或者就对象不会互相影响，此方法与buf.copy（buf.readerIndex（），buf.readableBytes（））相同。拷贝就对象所有可读的二进制到新对象当中。此方法不会修改旧对象的此readerIndex或writerIndex属性

package com.ht.web.google;

import java.math.BigInteger;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.interfaces.RSAPrivateCrtKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.Arrays;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.ByteBufAllocator;
import org.springframework.util.Base64Utils;

public class Rsa {

  public static void main(String[] args) throws Exception {
    ByteBuf buf = ByteBufAllocator.DEFAULT.buffer(8);

    //写入值
    buf.writeInt(128);

    //拷贝一个新对象，在新对象上修改不会影响前对象
    ByteBuf cp = buf.copy();

    //返回0-4 readerIndex和writerIndex不受copy方法影响
    System.out.println("readerIndex=" + buf.readerIndex() + "| writerIndex=" + buf.writerIndex());

    //修改前对象的值
    cp.setInt(0, 126);

    //修改值互不相信
    System.out.println(buf.readInt());
    System.out.println(cp.readInt());

    //全部需要释放
    buf.release();
    cp.release();
  }

}

返回共享缓冲区，新旧bytebuf共享一个缓冲区，修改内容会互相影响，调用duplicate不会修改readerIndex或writerIndex的值，新旧缓冲区都维护独立的索引Index，新返回的缓冲区不需要进行释放（increased）。

package com.ht.web.google;

import java.math.BigInteger;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.interfaces.RSAPrivateCrtKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.Arrays;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.ByteBufAllocator;
import org.springframework.util.Base64Utils;

public class Rsa {

  public static void main(String[] args) throws Exception {
    ByteBuf buf = ByteBufAllocator.DEFAULT.buffer(8);

    //写入值
    buf.writeInt(128);

    //拷贝一个新对象，在新对象上修改不会影响前对象
    ByteBuf cp = buf.duplicate();

    //返回0-4 readerIndex和writerIndex不受duplicate方法影响
    System.out.println("readerIndex=" + buf.readerIndex() + "| writerIndex=" + buf.writerIndex());

    //修改前对象的值
    cp.setInt(0, 126);

    //共享一块缓冲区，修改互相影响
    System.out.println(buf.readInt());
    System.out.println(cp.readInt());

    //不需要全部需要释放，只需要释放buf
    buf.release();

    //它不需要释放
    //cp.release();
  }

}

public static void main(String[] args) throws Exception {
    ByteBufAllocator allocator = PooledByteBufAllocator.DEFAULT;
    ByteBuf original = allocator.directBuffer(32);
    original.writeByte(1);
    original.writeByte(2);
    original.writeByte(3);
    original.writeByte(4);

    original.readByte();
    original.readByte();

    //分配子缓冲区，复制是从原始缓冲区readerIndex开始
    ByteBuf sub = original.slice();
    sub.readerIndex(0);
    //所以slice配的缓冲区自有2个可读字节
    System.out.println(sub.readableBytes());

    //分配子缓冲区，整个复制
    ByteBuf duplicate = original.duplicate();
    duplicate.readerIndex(0);
    //所以duplicate配的缓冲区自有4个可读字节
    System.out.println(duplicate.readableBytes());
}

duplicate负责原始缓冲区整个空间，默认r，w位置与原始缓冲区一致。

public DuplicatedByteBuf(ByteBuf buffer) {
        //原始缓冲区， 原始缓冲区当前rw位置
        this(buffer, buffer.readerIndex(), buffer.writerIndex());
    }

    DuplicatedByteBuf(ByteBuf buffer, int readerIndex, int writerIndex) {
        super(buffer.maxCapacity());

        if (buffer instanceof DuplicatedByteBuf) {
            this.buffer = ((DuplicatedByteBuf) buffer).buffer;
        } else if (buffer instanceof AbstractPooledDerivedByteBuf) {
            this.buffer = buffer.unwrap();
        } else {
            this.buffer = buffer;
        }

        setIndex(readerIndex, writerIndex);
        markReaderIndex();
        markWriterIndex();
    }