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From Jörg Schaible <joerg.schai...@gmx.de>
Subject Re: [imaging] Closing stream
Date Fri, 25 Oct 2013 15:24:29 GMT
Hi Damjan,

Damjan Jovanovic wrote:

> On Fri, Oct 25, 2013 at 12:36 PM, Jörg Schaible
> <Joerg.Schaible@scalaris.com> wrote:
>> Hi Damjan,
>>
>> Damjan Jovanovic wrote:
>>
>> [snip]
>>
>> Thanks for explanation.
>>
>>> We would be able to adapt that for Java < 1.7 by swallowing the close
>>> exception instead of calling addSuppressed() on the primary exception,
>>> but the show stopper is catching and rethrowing the primary exception
>>> (Throwable), which javac < 1.7 refuses to compile because it doesn't
>>> do "Rethrowing Exceptions with More Inclusive Type Checking"
>>> (http://docs.oracle.com/javase/7/docs/technotes/guides/language/catch-multiple.html).
>>>
>>> But this would work and always sets succeeded correctly without
>>> catch/re-throw:
>>>
>>> final InputStream is = factoryMethodThatCanThrow();
>>> boolean succeeded = false;
>>> try {
>>>     try {
>>>         is.methodThatCanThrow();
>>>     } finally {
>>>     }
>>>     succeeded = true;
>>> } finally {
>>>     closeSafely(!succeeded, is);
>>> }
>>
>> I guess the nested try was unintentionally ;-)
>>
>> Cheers,
>> Jörg
> 
> Well that actually won't work, because the "succeeded = true;" will be
> skipped if there is a "return;" in the inner try.

Well, but this has to be done in our code, so we can either change it or set 
"succedded = true" before the return as well.

To mimic Java 7, we could also implement:

============= %< ===============
 Throwable t = null;
 try {
 } (catch IOException e) { t = e; throw e; }
 // ... another line for each checked exception
 } (catch RuntimeException e) { t = e; throw e; }
 } (catch Error e) { t = e; throw e; }
 } finally {
   closeSafely(t != null, is);
 }
============= %< ===============

but as commented, we have to add a catch for every checked exception, 
anotehr one for RuntimeException and one for Error. The approach with the 
succeeded flag seems easier ...

> Other than a custom Java compiler, I guess there's no clean way of
> doing this in Java < 1.7. There's really only option 2 - with being
> careful to always set succeeded correctly on all paths out of the try
> block. Almost like releasing memory in C.

Yep.

Cheers,
Jörg


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