Deep copy duplicate() of Java's ByteBuffer
java.nio.ByteBuf开发者_StackOverflowfer#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?
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;
}
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;
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);
}
}
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;
}
You'll need to iterate the entire buffer and copy by value into the new buffer.
I believe this should supply a full deep copy, including the mark, "out-of-bounds" data, etc...just in case you need the most complete sandbox-safe carbon copy of a ByteBuffer.
The only thing it doesn't copy is the read-only trait, which you can easily get by just calling this method and tagging on a ".asReadOnlyBuffer()"
public static ByteBuffer cloneByteBuffer(ByteBuffer original)
{
//Get position, limit, and mark
int pos = original.position();
int limit = original.limit();
int mark = -1;
try
{
original.reset();
mark = original.position();
}
catch (InvalidMarkException e)
{
//This happens when the original's mark is -1, so leave mark at default value of -1
}
//Create clone with matching capacity and byte order
ByteBuffer clone = (original.isDirect()) ? ByteBuffer.allocateDirect(original.capacity()) : ByteBuffer.allocate(original.capacity());
clone.order(original.order());
//Copy FULL buffer contents, including the "out-of-bounds" part
original.limit(original.capacity());
original.position(0);
clone.put(original);
//Set mark of both buffers to what it was originally
if (mark != -1)
{
original.position(mark);
original.mark();
clone.position(mark);
clone.mark();
}
//Set position and limit of both buffers to what they were originally
original.position(pos);
original.limit(limit);
clone.position(pos);
clone.limit(limit);
return clone;
}
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