从ByteBuffer创建一个DataBufferUShort

Question

(Oracle Java 1.7, Eclipse Kepler, Ubuntu 12.04 64 bit)

I need to create a DataBufferUShort from a ByteBuffer but all my attempts have failed at run time..

How is this done, por favor ?

Here is one failure: ( java.lang.UnsupportedOperationException )

        ShortBuffer sBuf = imageData.asShortBuffer(); // ByteBuffer
    DataBufferUShort dataBufferUShort = new DataBufferUShort(sBuf.array(),
            nPixels);

Here's the stack trace. Line 156 is the second line in the code snippet above.

 Exception in thread "main" java.lang.UnsupportedOperationException
at java.nio.ShortBuffer.array(ShortBuffer.java:959)
at psw.iu.CreateImage.createGrayscaleImage(CreateImage.java:156)
at psw.iu.TestCreateImage.<init>(TestCreateImage.java:48)
at psw.iu.TestCreateImage.main(TestCreateImage.java:16)

Here's the method that creates the ByteBuffer

    public static ByteBuffer createScaledData(WorkingByteBuffer rawWBB,
        ByteBuffer scaledByteBuffer) {

    rawWBB.byteBuffer.rewind(); // byteBuffer is a ByteBuffer
    scaledByteBuffer.rewind();
    ShortBuffer inBuf = rawWBB.byteBuffer.asShortBuffer();
    ShortBuffer outBuf = scaledByteBuffer.asShortBuffer();
    inBuf.rewind();
    outBuf.rewind();
    int maxDN = MAX_USHORT;
    double scaleFactor = (double) maxDN / (double) range;

    while (inBuf.hasRemaining()) {
        int value = 0xffff & inBuf.get();
        int scaledValue = (int) ((double) (value - min) * scaleFactor + 0.5);
        if (scaledValue < 0)
            scaledValue = 0;
        if (scaledValue > maxDN)
            scaledValue = maxDN;
        outBuf.put((short) scaledValue);
    }

    return scaledByteBuffer;

}

Edit This gives no errors but it's not the solution I was looking for.

        imageData.rewind();
    ShortBuffer shortBuffer = imageData.asShortBuffer();
    shortBuffer.rewind();
    DataBufferUShort dataBufferUShort = new DataBufferUShort( nLines * nPixPerLine);
    int index = 0;
    while(shortBuffer.hasRemaining()){
        dataBufferUShort.setElem(index++, 0xffff & shortBuffer.get());
    }

Answer 1

The ShortBuffer you are creating is only a view of the ByteBuffer, and view buffers don't support array(). You need to create a 'real' ShortBuffer with ShortBuffer.allocate(), and copy the data into it via sbuff.get() from the ByteBuffer (flipping the latter first).

Answer 2

The ShortBuffer.array() method will only return an array if the original ShortBuffer was created with a short[] . in your case, your ShortBuffer is actually built on top of a byte[] (held by the ByteBuffer), so this won't work.

if you really need a short[], then you will need to copy the contents of the ShortBuffer to a short[]. something like:

short[] shorts = new short[sBuf.remaining()];
sBuff.get(shorts);