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From "SörenStraßfeld" <nc-stras...@netcologne.de>
Subject Re: External libraries in the bootclasspath
Date Fri, 14 Apr 2006 16:16:30 GMT
Paulex Yang schrieb:

of course I trust every apache library blind to be downward compatible, but not
down to 0.0.1 pre Alpha rc1 ;)

> Soeren Strassfeld wrote:
>> Ilya Neverov schrieb:
>>
>> Hi Ilya,
>>
>> just followed your link, as I understand it, the endorsed mechanism is only
for API Classes, which
>> are developed outside the JCP. This contains the org.w3c, org.xml and the
CORBA/omg packages, but
>> not internally used packages. I guess sun in some way trusts those library
vendors to be downward
>> compatible, and so not break the API.
> I guess Harmony also trusts the introduced external dependent classlib.;)
>> And as you said, the endorsed.dir is only for newer versions of libraries
(the docs explicitly
>> points to this as well), so Applications, which depend on older versions,
would still fail.
>>
> Jar versioning is a difficult issue in Java world (in fact more significant on
Java EE world), maybe the official solution(I mean, the standard) is JSR-277,
but we probably need to wait for Java 7 to provide the spec and RI. Not sure if
other component mechanism like OSGi has provided good idea on this issue?
>> Thanks,
>> Soeren
>>
>>> Hi,
>>>
>>> I think we can follow standardized way in this case.
>>>
>>>  On 4/11/06, Stepan Mishura <stepan.mishura@gmail.com> wrote:
>>>
>>>> There are no other opinions but I believe this issue needs broader
attention
>>>> so I'd like to start another thread.
>>>>
>>>> Harmony has a number of external libraries on the bootclasspath: ICU4C,
>>>> Xerces/Xalan. What if an app. uses the same library but another version?
>>>> What if library versions are not compatible? The possible way to resolve
the
>>>> issue to perform repackaging (i.e. put everything external under
>>>> org.apache.harmony namespace, however I'm not sure that this applicable for
>>>> ICU4C library).
>>>>
>>>> Are there other options?
>>>>
>>>
>>> Since J2SE 1.4 SUN introduced "Endorsed Standards Override Mechanism"
>>> for helping users to survive with rapidly evolving versions of popular
>>> libraries. This mechanism allows overriding implementation of some
>>> packages included in JRE bundle; the list of packages can be found at
>>> [1].
>>>
>>> Moreover, user can install external library providing version of
>>> related public API which is newer than API included in given JRE and
>>> this newer version of API becomes available for applications instead
>>> of the version bundled with the JRE. This is intended for supporting
>>> external API-s which are standardized outside of JCP, like CORBA or
>>> SAX and DOM for XML processing. You can run an app on J2SE 1.4 with
>>> DOM Level 3 API instead of DOM Level 2 bundled with jdk 1.4.
>>>
>>> It's quite easy-to-use mechanism – just put library's jar-files to the
>>> <java-home>/lib/endorsed directory or point to their location with the
>>> system property 'java.endorsed.dirs'. I suspect that it's easy for
>>> implementation also. Looks like that putting referred jar-files before
>>> system jar-files in bootclasspath would be enough to have such magic
>>> :) I'm not sure that any certified JRE does check that provided
>>> jar-files contain classes only related to the list of packages in [1]
>>> so we would be compatible with them in this place.
>>>
>>> [1]  http://java.sun.com/j2se/1.5.0/docs/guide/standards/index.html
>>>
>>>
>>>> Thanks,
>>>> Stepan Mishura
>>>> Intel Middleware Products Division
>>>>
>>>
>>> Thank you.
>>> Ilya Neverov,
>>> Intel Middleware Products Division
>>>
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>>>
>>>
>>
>>
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>>
>
>



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