Deep copy duplicate() of Java's ByteBuffer

问题

java.nio.ByteBuffer#duplicate() returns a new byte buffer that shares the old buffer's content. Changes to the old buffer's content will be visible in the new buffer, and vice versa. What if I want a deep copy of the byte buffer?

回答1:

I think the deep copy need not involve byte[]. Try the following:

public static ByteBuffer clone(ByteBuffer original) {
       ByteBuffer clone = ByteBuffer.allocate(original.capacity());
       original.rewind();//copy from the beginning
       clone.put(original);
       original.rewind();
       clone.flip();
       return clone;
}

回答2:

As this question still comes up as one of the first hits to copying a ByteBuffer, I will offer my solution. This solution does not touch the original buffer, including any mark set, and will return a deep copy with the same capacity as the original.

public static ByteBuffer cloneByteBuffer(final ByteBuffer original) {
    // Create clone with same capacity as original.
    final ByteBuffer clone = (original.isDirect()) ?
        ByteBuffer.allocateDirect(original.capacity()) :
        ByteBuffer.allocate(original.capacity());

    // Create a read-only copy of the original.
    // This allows reading from the original without modifying it.
    final ByteBuffer readOnlyCopy = original.asReadOnlyBuffer();

    // Flip and read from the original.
    readOnlyCopy.flip();
    clone.put(readOnlyCopy);

    return clone;
}

If one cares for the position, limit, or order to be set the same as the original, then that's an easy addition to the above:

clone.position(original.position());
clone.limit(original.limit());
clone.order(original.order());
return clone;

回答3:

Based off of mingfai's solution:

This will give you an almost true deep copy. The only thing lost will be the mark. If orig is a HeapBuffer and the offset is not zero or the capacity is less than the backing array than the outlying data is not copied.

public static ByteBuffer deepCopy( ByteBuffer orig )
{
    int pos = orig.position(), lim = orig.limit();
    try
    {
        orig.position(0).limit(orig.capacity()); // set range to entire buffer
        ByteBuffer toReturn = deepCopyVisible(orig); // deep copy range
        toReturn.position(pos).limit(lim); // set range to original
        return toReturn;
    }
    finally // do in finally in case something goes wrong we don't bork the orig
    {
        orig.position(pos).limit(lim); // restore original
    }
}

public static ByteBuffer deepCopyVisible( ByteBuffer orig )
{
    int pos = orig.position();
    try
    {
        ByteBuffer toReturn;
        // try to maintain implementation to keep performance
        if( orig.isDirect() )
            toReturn = ByteBuffer.allocateDirect(orig.remaining());
        else
            toReturn = ByteBuffer.allocate(orig.remaining());

        toReturn.put(orig);
        toReturn.order(orig.order());

        return (ByteBuffer) toReturn.position(0);
    }
    finally
    {
        orig.position(pos);
    }
}

回答4:

One more simple solution

public ByteBuffer deepCopy(ByteBuffer source, ByteBuffer target) {

    int sourceP = source.position();
    int sourceL = source.limit();

    if (null == target) {
        target = ByteBuffer.allocate(source.remaining());
    }
    target.put(source);
    target.flip();

    source.position(sourceP);
    source.limit(sourceL);
    return target;
}

回答5:

You'll need to iterate the entire buffer and copy by value into the new buffer.

来源：https://stackoverflow.com/questions/3366925/deep-copy-duplicate-of-javas-bytebuffer

标签

java

nio

deep-copy

bytebuffer