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Newsgroups: comp.lang.java.programmer
Date: Thu, 28 Feb 2019 13:44:33 -0800 (PST)
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Subject: Re: it's Closeable, but I don't want to close() it yet.
From: Eric Douglas <e.d.programmer@gmail.com>
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On Wednesday, February 27, 2019 at 10:52:01 AM UTC-5, Andreas Leitgeb wrote:
> In my application there exists an entity that is Closeable.
> It is kept in some class, and other parts of my application
> request a ref to the entity and do actions on it, then drop
> their ref, leaving the entity intact.
> 
> Everything runs fine, except eclipse warns me about spots
> where the entity is requested, used, and then dropped.
> Eclipse thinks it might need to be close()d.
> 
> Apart from ignoring the warning per eclipse settings or
> adding @SuppressWarnings, is there maybe a way to tell
> the compiler that a certain ref is not meant to be close()d?
> Letting it know that - despite the entity's ultimate fate of
> being eventually closed - this is not yet the time&place for it?

One last fun scenario.  ImageIO.read actually reads an InputStream and closes it.  So I do this and it works fine, but Eclipse throws a potential resource leak warning on mciis:

try {
 final MemoryCacheImageInputStream mciis = new MemoryCacheImageInputStream(is);
 myBufferedImage = ImageIO.read(mciis);
} catch (final IOException e) {
 return null;
}

Passing in ByteArrayInputStream is containing the bytes of a proper image file, the above code does not hit the exception, and works fine despite the warning.  Now if you attempt to close it to avoid that warning:

try (final MemoryCacheImageInputStream mciis = new MemoryCacheImageInputStream(is)) {
 myBufferedImage = ImageIO.read(mciis);
} catch (final IOException e) {
 return null;
}

This does hit the exception.