ImageIO.createImageOutputStream returns null

I am using the TwelveMonkey TIFF plugin to save TIFF files to a network share that is connected as NFS.

On one computer that I use (Windows 7) this appears to work flawlessly. However on another computer (Windows 10) I get an occasional issue where ImageIO.createImageOutputStream returns null.

Here is a snippet of the problematic code:

        File directory = new File(this.savePath);
        if (!directory.exists()) { directory.mkdirs(); }
        File file = Paths.get(this.savePath, fullFileName).toFile(); 
        try (ImageOutputStream outStream = ImageIO.createImageOutputStream(file)) {
            writer.setOutput(outStream);
            writer.prepareWriteSequence(null); //null means we will use the default streamMetadata.
        ...

It seems that for roughly 1 out of 3 runs of this code the outputStream gets returned as null. This then correctly causes an exception to be thrown at writer.setOutput(outStream.

How can I figure out why the plugin is failing to create an outputStream?

[nanthony21]

So, in todays testing I did in fact see a stack trace printed out and you were right about the cause.

Here is the stack trace:

java.io.FileNotFoundException: Z:\Nick\test2\Cell2\PWS\pws.tif (The system cannot find the path specified)
	at java.io.RandomAccessFile.open0(Native Method)
	at java.io.RandomAccessFile.open(RandomAccessFile.java:316)
	at java.io.RandomAccessFile.<init>(RandomAccessFile.java:243)
	at javax.imageio.stream.FileImageOutputStream.<init>(FileImageOutputStream.java:69)
	at com.sun.imageio.spi.FileImageOutputStreamSpi.createOutputStreamInstance(FileImageOutputStreamSpi.java:55)
	at javax.imageio.ImageIO.createImageOutputStream(ImageIO.java:419)

I noticed that this only happens when there isn’t a break point that results in a pause between creating the File and calling createImageOutputStream so it’s probably something to do with timing.

I’ll have to do some more reading about RandomAccessFile, hopefully I can make the program briefly pause until the File is read to be passed in to createImageOutputStream.

Since this is clearly not related to TwelveMonkeys I’ll go ahead and close this. Thanks for the help!

[nanthony21]

Thanks @haraldk , I’ll see if I can dig into what is going on in com.sun.imageio.spi.FileImageOutputStreamSpi.

When looking at the output in the debugger I didn’t see any stack traces coming up which makes me think that the null I was getting may actually come directly from ImageIO.createImageOutputStream:

        while (iter.hasNext()) {
            ImageOutputStreamSpi spi = (ImageOutputStreamSpi)iter.next();
            if (spi.getOutputClass().isInstance(output)) {
                try {
                    return spi.createOutputStreamInstance(output,
                                                          usecache,
                                                          getCacheDirectory());
                } catch (IOException e) {
                    throw new IIOException("Can't create cache file!", e);
                }
            }
        }

        return null;