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From Matt Benson <gudnabr...@gmail.com>
Subject Re: Backporting try-with-resources to Java < 7 (was: Re: [imaging] Closing stream)
Date Mon, 04 Nov 2013 15:21:43 GMT
On Nov 4, 2013 1:12 AM, "Damjan Jovanovic" <damjan@apache.org> wrote:
>
> For the record, I would only use this for imaging >= 2.0.
>
> Weaver looked undocumented and undecipherable to me, but let me look at it
> again slowly.

Tell me how you really feel! :-)

More seriously, tell me how to fix these problems. There is an outstanding
request for a basic how-to doc from the user perspective. Most likely there
should be a guide to writing a Weaver module as well.

Matt

>
> Damjan
>
>
> On Sun, Nov 3, 2013 at 9:14 PM, Matt Benson <gudnabrsam@gmail.com> wrote:
>
> > I wasn't under the impression this was blocking imaging 1.0. In any
case,
> > framing Damjan's work as a Weaver module would still use the same work
he's
> > done with ASM and would really only utilize a standard mechanism for
> > triggering the process. It would also avoid proliferation of multiple
maven
> > plugins with essentially the same mission: post-processing bytecode.
> >
> > Matt
> > On Nov 3, 2013 10:08 AM, "Gary Gregory" <garydgregory@gmail.com> wrote:
> >
> > > On Sun, Nov 3, 2013 at 10:56 AM, Matt Benson <gudnabrsam@gmail.com>
> > wrote:
> > >
> > >> Sounds like it would be trivial to frame what you've done here into
the
> > >> context of a Weaver module, for which there exist both a maven plugin
> > and
> > >> an Antlib, as well as a need for a near-term release. :-)
> > >>
> > >
> > > and eating our own dog food :)
> > >
> > > We may pushing the limits of Dajman's patience for a 1.0 which is long
> > > overdue.
> > >
> > > I suppose D needs to weigh using ASM or [weaver] vs. adjusting the
> > current
> > > code with Java 5.
> > >
> > > Gary
> > >
> > >>
> > >> Matt
> > >> On Nov 3, 2013 2:30 AM, "Damjan Jovanovic" <damjan@apache.org> wrote:
> > >>
> > >> > On Fri, Oct 25, 2013 at 1:52 PM, Matt Benson <gudnabrsam@gmail.com>
> > >> wrote:
> > >> >
> > >> > > On Oct 25, 2013 6:30 AM, "Damjan Jovanovic" <damjan.jov@gmail.com
>
> > >> > 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.
> > >> > > >
> > >> > > > 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.
> > >> > > >
> > >> > >
> > >> > > I haven't deeply followed this conversation, but would this be
a
> > >> > candidate
> > >> > > for a [weaver] module?
> > >> > >
> > >> > > Matt
> > >> > >
> > >> > >
> > >> >
> > >> > [weaver] I am less sure about, but by playing with Objectweb's ASM
I
> > did
> > >> > manage to compile code with try-with-resources on Java 7, change
the
> > >> class
> > >> > file version, do some bytecode manipulation to delete calls to
> > >> > Throwable.addSuppressed(), and get it to work on Java < 7.
> > >> >
> > >> > Made it into a Maven plugin and it works well :). Also verified
other
> > >> Java
> > >> > 7 language features (binary literals, underscores in numeric
literals,
> > >> > strings in switch, diamonds, exception multi-catch and re-throw)
work
> > on
> > >> > Java < 7 because they're just syntactic sugar.
> > >> >
> > >> > It's very small and simple - 143 lines in 1 file. Is it worth
adding
> > as
> > >> a
> > >> > new commons project? Or do we not host (projects that contain)
Maven
> > >> > plugins?
> > >> >
> > >> > Damjan
> > >> >
> > >>
> > >
> > >
> > >
> > > --
> > > E-Mail: garydgregory@gmail.com | ggregory@apache.org
> > > Java Persistence with Hibernate, Second Edition<
> > http://www.manning.com/bauer3/>
> > > JUnit in Action, Second Edition <http://www.manning.com/tahchiev/>
> > > Spring Batch in Action <http://www.manning.com/templier/>
> > > Blog: http://garygregory.wordpress.com
> > > Home: http://garygregory.com/
> > > Tweet! http://twitter.com/GaryGregory
> > >
> >

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