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From Ron Wheeler <rwhee...@artifact-software.com>
Subject Re: How to put a dependency in the classpath BEFORE jre.jar?
Date Mon, 24 Sep 2012 19:48:25 GMT
On 24/09/2012 1:42 PM, Markus KARG wrote:
> Stephen,
>
> I did never suggest to modify the POM and said no word about any future form
> of the POM, so I skip your comments about that and right go on with the idea
> of a Platform:
>
>> I like some of your idea about the concept of a platform but this is
>> not as trivial as you think.
>>
>> There is the issue of building with JDK5 an artifact to be run on JDK5
>> or
>> JDK6
> The idea of having a Platform interface actually solves exactly that
> problem, since the JDK5 platform will tell how to build on JDK5, while the
> JDK6 platform will tell how to build on JDK6.
Are you sure that you mean build? What are you building that is different?
It still sounds like an installation issue and "Package" is what an 
installer builder creates.
Maven will build the modules that you need to create the package of jars 
that gets installed.

>
>> There is the issue of somebody building their own patched JAX-RS and
>> publishing at their own coordinates... how would the "platform" know
>> that "com.foobar.manchu:jersey-patched-by-bob:0.1.2" is supposed to be
>> endorsed... other than by scanning the jar file and looking for paths
>> within....
> For this, there is a Java standard already: The spec and impl information in
> the MANIFEST.MF file of the JAR was invented exactly to answer this
> question. No need to parse or scan anything, just applying a well-known,
> very old and approved standard!
>
>> What do we do when building a .WAR that includes that dependency?
> I do not see what shall be the problem with a WAR? For compiling it, you
> need the dependency. Whether or not it is endorsed or not, is decided by the
> Platform. What endorsed specs it implements is to be found in its
> MANIFEST.MF.
>
> Can you describe the problem that you see?
At build time you need to specify "provided" or "compile" to specify if 
you want the dependency in the jar or not.
If you need both configuration of wars, then you need  2 Maven projects.
They should be both very thin with none of your code in the project.
>> Please file a JIRA so that your platform idea does not get lost in the
>> ML, but I don't think in its current shape that it is the right
>> solution.
> Do you honestly think it is worth getting filed if it is not the right
> solution?
It would get the need onto the official list of enhancements.
>> I would be more thinking along the lines of a "platform" packaging
>> type...
> ...which implies a POM change...
>
>> coupled with the "provides" (sort of inverse of dependencies) element
>> or scope...
>>
>> My reasoning is this... when you need to replace an "endorsed"
>> dependency what you are really saying is "I *need* to run on a
>> different platform"
>>
>> The Endorsed mechanism is just a way of modifying the platform that you
>> run on without having to produce a custom build of that platform...
>>
>> So to my mind, you create modules for the platforms that you require...
>> those platforms have their dependencies listed as either <provides>
>> elements in a model 5 pom, or as <scope>provides</scope> (in a model
5
>> pom again... because unfortunately the allowed values of the scope
>> element are locked in model 4) so we can filter the dependencies
>> appropriately...
> If I understand correctly, then you simply will replace the Platform
> interface by a Platform packaging type, hence allowing people to easily
> defined their own platform? Well, why not? Do you file a JIRA for this?
>
>> It would be nice if we could find a way of building the same module for
>> multiple platforms at the same time... but the key here is to realize
>> that it is not the .jar that you build for a platform... but the
>> "executable .jar" or the ".war" or the ".ear", etc that you build for
>> the platform...
>> so those would be "thin" modules, and duplication of modules is less of
>> an issue... IOW one module per platform... though nothing to stop
>> multiple executions of the maven war plugin with the different
>> platforms configured... works too because (bar skinny wars in ear) .war
>> files are a final end of the chain artifact.
> I think this is not correct: For example, there might be difference in a
> "thin" JAR for Java 5 to Java 6, too. For example, if it is not a complete
> library that you depend upon (hence is endorsed), but if it is one or two
> single classes that exist in Java 6 but did not in Java 5 so you ship them
> *within* the Java 5 release of your "thin" JAR.
You would want to put that difference in the "skinny" war not in your 
main code jar.
Your code jar should not care about Java 5 or Java 6 since the only 
difference in your example is that the skinny war for 5 will have one or 
two extra helper classes that make up for the functionality that you 
need that is not included.

>
>> [In fact, if we look at this from a better decomposition PoV might make
>> more sense to have a "webapp" packaging that holds the .war content and
>> make .war a final end of the line artifact... but getting sidetracked
>> again]
>>
>> With this model... you would also see platforms for each of the JavaEE
>> containers, as well as a generic JavaEE specification platform...
>>
>> [the "webapp" packaging then becomes more needed... think of skinny
>> .wars being packaged into a .ear for each platform that you want to
>> deploy the .ear onto... on older platforms you might need the newer
>> version of JSF, on TomEE you may need additional dependencies because
>> it is implementing one profile, etc]
>>
>> IOW I think the concept of a platform is a good idea... but there is a
>> lot more to it than meets the eye.
> Never said that it will be easy. But we *need* platforms in Maven 4. Either
> way.
I still think that you are trying to make a build tool do the job of an 
installation tool.
Nothing in this discussion yet makes me believe that maven is the right 
way to solve this.
A Maven solution is going to be difficult to configure and is likely to 
make Maven even more intimidating than it is already.

Ron
>> -Stephen
>>
>> P.S.
>>
>> I am quite sure others will come along and poke holes in my ideas above
>> too!
>>
>> On 22 September 2012 10:19, Markus KARG <markus@headcrashing.eu> wrote:
>>
>>> Stephen,
>>>
>>> if we would never address problems that seem hard to fix at first
>>> sight, then the Maven core would never evolve and other system would
>>> take over some day. So a discussion like this one is essential for
>> the
>>> future of this tool.
>>> There are too much things left open due to concerns like these (e. g.
>>> see the long lasting discussion about SNAPSHOTs being included in
>>> version ranges), so we should start solving them step by step instead
>>> of flinching due to virtual efforts. :-)
>>>
>>> So let me chime in here and start a discussion by throwing a proposal
>>> in the
>>> ring: Introduction of the "Platform" interface in Maven 4!
>>>
>>> Possibly the best way to resolve the endorsed dependency problem
>>> mid-term would be to understand how it comes to the endorsed-ness:
>>> Obviously this is because someone in an official position (like the
>>> JCP) decides that something that was a "normal" dependency before now
>>> is "pre-packaged" with the official runtime package (like the JRE).
>> In
>>> the end, that means, that Maven has to know about that decision to be
>> able to deal with its effects.
>>> Looking it this way I have to contradict in part:
>>>
>>> * This is _not_ a Java-only problem, as potentially there could be
>>> endorsed libraries in other runtime systems, too, like .NET or Flash,
>>> or even Win32 (for example, I can vividly remember that "GDI+" first
>>> was a custom DLL that everyone had to ship with his own application
>>> EXE, but later it was part of the official Windows SDK, pre-packaged
>>> with the operating system; same with newer ODBC releases BTW). While
>> I
>>> do not say that those named examples in fact do have an endorsement
>>> facility (obvisouly besides Win32 where I named two examples), it
>>> could be possible that _some_ other Maven-supported platform _will_
>>> have such a facility now or in future. So as it is not a Java-only
>>> problem, it makes sense to have a _common_ solution.
>>>
>>> * It is _not_ a problem of scope, since scope is to be defined solely
>>> by the view of the using dependent project always. If the dependent
>>> project needs this library for test only, scope still is 'test' (e.
>> g.
>>> a Win32 program might need a particular release of ODBC for an
>>> integration test, while at runtime it possibly might never use ODBC
>> at
>>> all). The fact that a library was in user space in JRE 5 but is in
>>> system space in JRE 6 does not have any influence on this project's
>>> use, hence, of the scope. So there is no need for another scope.
>>>
>>> * Endorsed libraries are _not_ a problem of one particular dependent
>>> project, but an inherent decision of the platform itself (_every_
>>> dependent project on this particular platform (JRE 6 in this example)
>>> suffer from the _same_ pain, as _the platform_ decides that this is
>>> endorsed, but neither the dependent project nor the dependency
>>> itself). So it is nothing to get configured in neither the dependent
>>> POM nor in the dependency's POM, but it is solely a third place that
>>> makes up the endorsed-ness: The POM of the "platform" (here: the POM
>>> of a hypthetical artifact that makes up what we know as "JRE 6").
>> Which simply does not exist in Maven 3 AFAIK.
>>> * As a result, it is _not_ a particular problem of the compiler,
>> since
>>> _all_ compilers (jikes, javac, eclipse) need to support endorsed
>>> libraries. As all compilers might have different configuration
>>> switches, and selection of the particular compiler might be out of
>>> scope of the POM (i. e. defined in company pom for example), it
>> simply
>>> is no sophisticated solution to provide particular javac options
>>> inside of each single dependent POM.
>>>
>>> * So as AFAIK Maven 3 does not yet know the concept of "Platform"
>>> modules, the solution obviously is to add this new concept to Maven
>> 4:
>>> Strip the knowledge about the different platforms (hence, JREs) from
>>> the lots of plugins (like the compiler-plugin or the jar-plugin) into
>>> one single artifact which forms the "JRE 6 Platform" (including some
>>> general "Platform"
>>> interface common not only for the JREs but for all kinds of
>> "Platforms"
>>> like
>>> .NET and Flash etc.). Using this interface, Maven could resolve the
>>> question "Is this dependency to be put in the root classpath, or in
>>> the user classpath?" automatically. Maven simply needs to ask the
>>> platform (using the new interface) what the right classpath is, and
>>> the platform would answer with either 'User' or 'System'
>>> (interface-defined enum constants for example). So the JRE 5 might
>>> answer with 'User' while JRE 6 might answer with 'System' for the
>> same
>>> dependency! No need for _any_ configuration in the POM! No need for
>>> _any_ POM schema change! Maven could simply set up the root classpath
>>> fully automatically that way!
>>>
>>> Just like one day Eclipse learned the difference between "JRE" and
>> the
>>> general term "Platform", Maven 4 has to learn this concept, too.
>>>
>>> Maybe I should file a RFE for this?
>>>
>>> Regards
>>> Markus
>>>
>>>> -----Original Message-----
>>>> From: Stephen Connolly [mailto:stephen.alan.connolly@gmail.com]
>>>> Sent: Samstag, 22. September 2012 00:09
>>>> To: Maven Users List
>>>> Subject: Re: How to put a dependency in the classpath BEFORE
>> jre.jar?
>>>> 1. Maven is not just about java (though very java focused I admit)
>>>> endorsed does not make sense outside of java 2. Whether a
>> dependency
>>>> needs to be endorsed or not depends on the jvm version it
>> targets...
>>>> A dep can be fine until it gets added to the jvm spec.
>>>> 3. It should probably more correctly be <scope>endorsed</scope>
4.
>>>> Where would you package an endorsed dependency within a .war or
>> .ear
>>>> file?
>>>>
>>>> And don't get me started on the fact that to change this requires
>>>> changing the Pom format (which potentially could break ivy, gradle,
>>>> leinengen, sbt,
>>>> etc)
>>>>
>>>> Not an easy problem to solve, but I feel your pain
>>>>
>>>> On Friday, 21 September 2012, Markus KARG wrote:
>>>>
>>>>> Thank you for pointing me to this excellent blog entry, but in
>>>>> fact I wonder why such a great tool like Maven doesn't have
>>>>> built-in support for endorsed dependencies? I mean, in the end a
>>>>> different compiler might break the solution, so it would be a
>> good
>>>>> idea if a dependency could simply marked as
>> <endorsed>true</endorsed>.
>>>>>> -----Original Message-----
>>>>>> From: Claves Do Amaral
>>>>>> [mailto:Claves.DoAmaral@igmarkets.com<javascript:;>
>>>>> ]
>>>>>> Sent: Donnerstag, 20. September 2012 10:30
>>>>>> To: Maven Users List
>>>>>> Subject: RE: How to put a dependency in the classpath BEFORE
>>>> jre.jar?
>>>>>> If I understand the problem well, this is equivalent to provide
>>>>>> endorsed libraries at runtime.
>>>>>> I have found this resource, that looks a bit dated, but it may
>>>> work.
>>>>>> Not sure if Maven 3 offers a better solution
>>>>>>
>>>>>> http://www.mindbug.org/2009/02/adding-endorsements-to-mavens-
>>>>>> plugins.html
>>>>>>
>>>>>> Claves
>>>>>>
>>>>>> -----Original Message-----
>>>>>> From: Markus Karg [mailto:karg@quipsy.de <javascript:;>]
>>>>>> Sent: 20 September 2012 09:22
>>>>>> To: users@maven.apache.org <javascript:;>
>>>>>> Subject: How to put a dependency in the classpath BEFORE
>> jre.jar?
>>>>>> I have a dependency on javaee.jar, which provides newer
>> versions
>>>> for
>>>>>> classes found in JRE's jre.jar (particularly the @Resource
>>>> annotation).
>>>>>> But javaee.jar is always appended to the classpath, while to be
>>>> able
>>>>>> to load the newer version, I need to PREFIX it before jre.jar
>>>>>> instead. How can I configure this in the POM?
>>>>>>
>>>>>>

-- 
Ron Wheeler
President
Artifact Software Inc
email: rwheeler@artifact-software.com
skype: ronaldmwheeler
phone: 866-970-2435, ext 102


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