JDK6 backwards compatible AutoCloseable from a librariesperspective

[Tom Ball]

Hacking javac seems easier -- just change the allowTryWithResources test and
the constant for the AutoCloseable classname so its package is outside of
java.lang.  The compiler changes I submitted to support ARM don't have any
other Java 7 dependencies, nor do they create Java 7-only output (aside from
the java.lang reference).  Although Oracle has changed what I submitted
(made it better, no doubt :-), it's unlikely they added anything that would
break this.

To hack javac, just clone langtools/ and follow its README for the build
instructions.

Tom

On Mon, Feb 7, 2011 at 6:32 AM, Rémi Forax <forax at univ-mlv.fr> wrote:

>  Le 07/02/2011 15:08, Michael Bien a écrit :
> >    On 02/07/2011 02:40 PM, Rémi Forax wrote:
> >>     Le 07/02/2011 14:10, Michael Bien a écrit :
> >>>      Hello everyone,
> >>>
> >>> I would like to support the new try-with-resource feature in jocl while
> >>> staying backwards compatible with JDK5/6. The problem is that
> >>> AutoCloseable resides in java.lang which means i have no chance to load
> >>> the class if i would ship it for jdk5 backwards compatibility.
> >>>
> >>> Providing two builds for JOCL is not what i would like to do just to be
> >>> able to be upwards compatible.
> >>>
> >>> any ideas what i could do in this situation?
> >>>
> >>> best regards,
> >>> michael
> >> You need to:
> >> Create a jocl internal equivalent to java.lang.AutoClosable, let say
> >> jocl.lang.AutoClosable,
> >> this class should extends java.lang.AutoClosable.
> >> modify you managed classes to implements  jocl.lang.AutoClosable.
> >> compile with javac -source 7 -target 7
> >> Now you have a 1.7 compatible version.
> >>
> >> The trick is to downgrade the classfiles to have a 1.5 compatible
> version.
> >> For this use a bytecode rewriter tools like ASM [1] to change a just
> >> some bits
> >> in the classfiles.
> >>      modify the classfile of jocl.lang.AutoClosable to don't inherits
> from
> >> java.lang.AutoClosable anymore.
> >>      downgrade the classfiles major version number from 51 (V1_7) to 49
> (V1_5)
> >>
> >> In fact, there is a way to avoid to create jocl.lang.AutoClosable, you
> can
> >> analyze the bytecode to detect call to AutoClosable.close() and replace
> it
> >> by the type of the variable infered using the same algorithm as the
> >> verifier does.
> >> ASM package org.objectweb.asm.analysis already provides this analysis.
> >>
> >> Rémi
> >>
> >> [1] http://asm.ow2.org/
> >>
> >>
> > Thank you Remi,
> >
> > do i really have to compile with 1.7 language level even if i don't use
> > ARM internally?
>
> yes, you have to.
> source of the compiler near line 165:
>
> http://hg.openjdk.java.net/jdk7/jdk7/langtools/file/1383d1ee8b5d/src/share/classes/com/sun/tools/javac/code/Source.java
>
> public boolean allowTryWithResources() {
>      return compareTo(JDK1_7)>= 0;
> }
>
>
> > -michael
>
> Rémi
>
>
>
>