-------- Original message -------- From: Damjan Jovanovic Date:11/03/2013 03:30 (GMT-05:00) To: Commons Developers List Subject: Backporting try-with-resources to Java < 7 (was: Re: [imaging] Closing stream)
On Fri, Oct 25, 2013 at 1:52 PM, Matt Benson <gudnabr...@gmail.com> wrote: > On Oct 25, 2013 6:30 AM, "Damjan Jovanovic" <damjan....@gmail.com> wrote: > > > > On Fri, Oct 25, 2013 at 12:36 PM, Jörg Schaible > > <joerg.schai...@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? We already host a build plug in of some kind IIRC with http://search.maven.org/#search%7Cga%7C1%7Ca%3A%22commons-build-plugin%22 Gary Damjan
