Netty java getting data from ByteBuf

Question

How to get a byte array from ByteBuf efficiently in the code below? I need to get the array and then serialize it.

package testingNetty; import io.netty.buffer.ByteBuf; import io.netty.channel.ChannelHandlerContext; import io.netty.channel.ChannelInboundHandlerAdapter; public class ServerHandler extends ChannelInboundHandlerAdapter { @Override public void channelRead(ChannelHandlerContext ctx, Object msg) { System.out.println("Message receive"); ByteBuf buff = (ByteBuf) msg; // There is I need get bytes from buff and make serialization byte[] bytes = BuffConvertor.GetBytes(buff); } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) { // Close the connection when an exception is raised. cause.printStackTrace(); ctx.close(); } }

Can you please post the complete code. Also mention the which version of netty you are using? — ajay_t
– ajay_t, Commented Oct 10, 2013 at 13:12
So what's problem is? What do you mean by bytes massive in the above context? — ajay_t
– ajay_t, Commented Oct 10, 2013 at 13:35
Bytes massive means a byte[] wich contains seriziable object — NiceTheo
– NiceTheo, Commented Oct 10, 2013 at 14:12

trustin · Accepted Answer · 2015-10-11 10:40:07Z

ByteBuf buf = ... byte[] bytes = new byte[buf.readableBytes()]; buf.readBytes(bytes);

If you don't want the readerIndex to change:

ByteBuf buf = ... byte[] bytes = new byte[buf.readableBytes()]; int readerIndex = buf.readerIndex(); buf.getBytes(readerIndex, bytes);

If you want to minimize the memory copy, you can use the backing array of the ByteBuf, if it's available:

ByteBuf buf = ... byte[] bytes; int offset; int length = buf.readableBytes(); if (buf.hasArray()) { bytes = buf.array(); offset = buf.arrayOffset(); } else { bytes = new byte[length]; buf.getBytes(buf.readerIndex(), bytes); offset = 0; }

Please note that you can't simply use buf.array(), because:

Not all ByteBufs have backing array. Some are off-heap buffers (i.e. direct memory)
Even if a ByteBuf has a backing array (i.e. buf.hasArray() returns true), the following isn't necessarily true because the buffer might be a slice of other buffer or a pooled buffer:
- buf.array()[0] == buf.getByte(0)
- buf.array().length == buf.capacity()

@user2132106 would like to know if he can do byte[] ar= buf.array() (if I understand the post correctly).
I tested with real data: the second way (minimize the memory copy) is wrong. Java platform: Oracle 1.8; netty version: 4.1.58.Final.
@Fireburn offset tells at which position in the array the first byte starts.

Lion · Accepted Answer · 2022-11-16 12:59:43Z

6

Another option is ByteBufUtil.getBytes(ByteBuf buf, int start, int length, boolean copy)

See ByteBufUtil

edited Nov 16, 2022 at 12:59

answered Sep 23, 2022 at 6:50

Lion

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2 Comments

Tuomas Kiviaho Over a year ago

There is indeed an option to share the array instead of copying it (if possible)

Lion Over a year ago

Thanks @TuomasKiviaho . I updated my answer per your comment.

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