Is it possible to create ByteBuffer from a List<ByteBuffer>?

Question

Let's say i have a list/arrayList or an array of ByteBuffers (List<ByteBuffer> or ByteBuffer[])

It is possible from this to directly get the bytes from the above array without iterating through all the items or computing their total size? I am looking for something like this:

ByteBuffer[] bufferList = new ByteBuffer[7]; //this can be any kind of list of ByteBuffers
//add items to the array
ByteBuffer buffer = (ByteBuffer) bufferList; //what i want to achieve

Of course the last line is not correct.

The thing is that i already have in the array all the bytes in order, but I want them not to be in a list anymore, but in a single ByteBuffer. So is there something that makes possible to create a ByteBuffer from a list/array of ByteBuffers?

Thank you!

You have individual ByteBuffer elements in an array or list that each have X bytes and you want to add all those bytes to a single ByteBuffer? — Sotirios Delimanolis
– Sotirios Delimanolis, Commented Aug 27, 2013 at 15:14
Make a new ByteBuffer, iterate through your array of buffers, get each bytebuffer as an array using .array(), and use put(byte[]) into your new ByteBuffer — Cruncher
– Cruncher, Commented Aug 27, 2013 at 15:16
Yes @SotiriosDelimanolis. I have a list of ByteBuffers that have different byte size and i want to create a single ByteBuffer from them. — dianap
– dianap, Commented Aug 27, 2013 at 15:18

Cruncher · Accepted Answer · 2017-05-17 10:35:18Z

4

public ByteBuffer convertToOne(ByteBuffer[] src)
{
    int size=0;
    for(int i = 0 ; i < src.length ; i++) {
        size+=src[i].array().length;
    }

    ByteBuffer newBuffer = ByteBuffer.allocate(size);

    int sizeAt = 0;
    for(int i = 0 ; i < src.length ; i++) {
        newBuffer.put(src[i].array(), sizeAt);
        sizeAt += src[i].array().length;
    }
    return newBuffer;
}

edited May 17, 2017 at 10:35

answered Aug 27, 2013 at 15:18

Cruncher

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11 Comments

dianap Over a year ago

the problem with this solution would be that i have to make another iteration to compute the elements total bytes size. (The ByteBuffer items don't have constant size) So the problem would be how i initialize the final ByteBuffer (the newBuffer in this case).

Cruncher Over a year ago

How do you initialize the original buffer? I'm assuming you have a concrete class somehwere.

dianap Over a year ago

then how do i create 'ByteBuffer dest' ? Don't i have to allocate the size before putting things into it?

Cruncher Over a year ago

There's no way around it. If java had a method to do this, it would be implemented by doing that anyway. Native java methods aren't magic.

Cruncher Over a year ago

There is only one way to create a ByteBuffer, by specifying size. Also, there are no ByteBuffer methods which return a ByteBuffer of a different size. It therefore then follows that you need to compute size first.

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Jeremy · Accepted Answer · 2013-08-27 15:14:58Z

0

I believe you're going to have to create a new ByteBuffer and copy each of the buffers in bufferList into the new one. You should put this functionality in a method so as to not repeat the code each time you use it.

answered Aug 27, 2013 at 15:14

Jeremy

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3 Comments

dianap Over a year ago

Yes. I know i can do this. but this will require to iterate through all the ByteBuffers to compute their total size, then create the big ByteBuffer, and the interate again to add them. I was looking for something more optimum, if it is possible.

Jeremy Over a year ago

Iterating over the collection is going to take a fraction of the time that creating the big ByteBuffer and copying the other ByteBuffers is going to take. Any built-in function is most likely going to do this anyway.

dianap Over a year ago

the issue is.. that i am trying to create a serializer, so in the end I need a single ByteBuffer not a list of ByteBuffers. That is why i want to transform a list of BB to a single BB

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