Hi Damjan,
Damjan Jovanovic wrote:
> On Thu, Oct 24, 2013 at 11:29 PM, Gary Gregory <garydgreg...@gmail.com>
> wrote:
>> On Thu, Oct 24, 2013 at 4:31 PM, Jörg Schaible
>> <joerg.schai...@gmx.de>wrote:
>>
>>> Hi Damjan,
>>>
>>> Damjan Jovanovic wrote:
>>>
>>> > As one of the perpetrators of the problem, I have now fixed it. The
>>> > reasons I swallowed exceptions were simple:
>>>
>>> [snip]
>>>
>>> > * when an exception is thrown and close() then throws another
>>> > exception, the close() exception is propagated and the original
>>> > exception - which could reveal the cause of the problem - swallowed
>>>
>>> [snip]
>>>
>>> And this *is* a real problem. And it is exactly why the IOException of
>>> close() are normally ignored. While I don't like
>>> IOUtils.closeQietly(closeable), I use normally a method
>>> "IO.closeLogged(closeable)" resp. "IO.closeLogged(closeable, logger)".
>>>
>>> If e.g. an image is corrupted and later on an additional exception
>>> occurs closing any resource, you will simply *never* learn about the
>>> corrupted image that caused the problem in first case. The original
>>> exception must never be swallowed!
>>>
>>
>> Nest'em!
>>
>> G
>
> What's the way forward though?
>
> 1. Catching both exceptions and nesting with setCause():
>
> InputStream is = null;
> Exception ex = null;
> try {
> is = factoryMethodThatCanThrow();
> is.methodThatCanThrow();
> } catch (Exception exx) {
> ex = exx;
> } finally {
> if (is != null) {
> try {
> is.close();
> } catch (IOException closeEx) {
> if (ex != null) {
> closeEx.setCause(ex);
> }
> throw closeEx;
> }
> }
> }
>
> which only gets worse, as each type of exception has to be separately
> caught and rethrown...
Right, you could have got even an OOME reading an image ... :-/
> 2. Swallowing close() exceptions when a succeeded flag at the end of
> the try wasn't set:
>
> InputStream is = null;
> boolean succeeded = false;
> try {
> is = factoryMethodThatCanThrow();
> is.methodThatCanThrow();
> succeeded = true;
> } finally {
> if (is != null) {
> try {
> is.close();
> } catch (IOException closeEx) {
> if (succeeded) {
> throw closeEx;
> }
> }
> }
> }
>
> which now also requires making sure you don't "return;" before the end
> of the try...
IMHO this is the best approach so far. Maybe we can introduce a utility
method somewhere to avoid the boilerplate copies:
=============== %< ==================
public static void closeSafely(boolean mayThrow, Closeable... closeables)
throws IOException {
IOException ioex = null;
for(Closeable closeable : closeables) {
if (closeable != null) {
try {
closeable.close();
} catch (IOException ex) {
ioex = ex; // keep first or last ?!?
}
}
}
if (mayThrow && ioex != null) {
throw ioex;
}
}
=============== %< ==================
> 3. Java 7 + try-with-resources, which will cripple portability to
> Android...
I would first write a unit test to see what Java 7 actually does with
multiple open resources in the different error cases.
Cheers,
Jörg
---------------------------------------------------------------------
To unsubscribe, e-mail: dev-unsubscr...@commons.apache.org
For additional commands, e-mail: dev-h...@commons.apache.org
