Remember that some API jars are used by more the the Jakarta EE platform implementations. And in those scenarios, you should be careful about forcing consumers to update to Java 11 when the can't or don't want to.
Using JUnit 5 as an example, they have a broad user community which includes those still targeting Java 8 runtimes and need to test there.
JSON Processing and RESTful Web Services may be somethings that are useful outside of the platform in a variety of scenarios and care must be taken with a decision to force consumers to Java 11. So while it places a build engineering burden on us to build mixed target jars, we can support a broad user community this way.
--
BJ Hargrave
Senior Technical Staff Member, IBM // office: +1 386 848 1781
OSGi Fellow and OSGi Specification Project lead // mobile: +1 386 848 3788
hargrave@xxxxxxxxxx
----- Original message -----
From: "Thomas Watson" <tjwatson@xxxxxxxxxx>
Sent by: "jakartaee-platform-dev" <jakartaee-platform-dev-bounces@xxxxxxxxxxx>
To: jakartaee-platform-dev@xxxxxxxxxxx
Cc:
Subject: [EXTERNAL] Re: [jakartaee-platform-dev] : Re: The location of module-info.java and muti release jar
Date: Fri, Oct 8, 2021 08:53
For Jakarta 10 it would be a bit more simple to move on to Java 11 and stop providing Java 8 targeted classes (+module-info.class). How important (or large) is the group of developers that want the latest and greatest Jakarta spec version but are unwilling to move to a more modern Java version?
I've used the double compile approach to generate a proper module-info.class for a Java 8 project. As you say, this does help generate and validate a proper module-info.class, but I've found that doesn't always play nicely when in an IDE.
Tom
----- Original message -----
From: "Lukas Jungmann" <lukas.jungmann@xxxxxxxxxx>
Sent by: "jakartaee-platform-dev" <jakartaee-platform-dev-bounces@xxxxxxxxxxx>
To: jakartaee-platform-dev@xxxxxxxxxxx
Cc:
Subject: Re: [jakartaee-platform-dev] [External] : Re: The location of module-info.java and muti release jar
Date: Thu, Oct 7, 2021 8:17 PM
On 10/7/21 9:39 PM, BJ Hargrave wrote:
> Some APIs may not want to step up to target Java 11 and will want to
> remain with target Java 8 for their API class files. In this case, they
> will need to compile module-info.java with target 11 and add that class
> file into the root of the jar. So there will be 2 compile steps in the
> build (one for module-info, and the other for the other classes).
My experience says having 2 complete compilations - first for everything
by 11, second everything minus module-info by 8 - is more reliable.
There were 2 sets of issues I faced when I was not following this:
1) java.lang.VerifyError (see
https://github.com/eclipse-ee4j/mail/issues/489 )
2) when module-info is compiled against pre-compiled classes, javac
won't issue warnings/errors for mistakes like missing "uses" and
probably others
...just saying...
thanks,
--lukas
> This is common practice in many projects. For example, see JUnit 5. All
> their jars have class files targeting Java 8 and also include a (target
> 11) module-info.class file in the root of the jar.
> A Java 8 runtime will not care about a module-info.class file in the jar
> and so will not attempt to load it. A Java 11 runtime will be able to
> load the module-info.class and the other target 8 class files just fine.
> That is, there is no need for the complexity of Multi-Release jars just
> to include a module-info.class file in a jar with other target 8 class
> files.
> --
>
> BJ Hargrave
> Senior Technical Staff Member, IBM // office: +1 386 848 1781
> OSGi Fellow and OSGi Specification Project lead // mobile: +1 386 848 3788
> hargrave@xxxxxxxxxx
>
> ----- Original message -----
> From: "Thomas Watson" <tjwatson@xxxxxxxxxx>
> Sent by: "jakartaee-platform-dev"
> <jakartaee-platform-dev-bounces@xxxxxxxxxxx>
> To: jakartaee-platform-dev@xxxxxxxxxxx
> Cc:
> Subject: [EXTERNAL] Re: [jakartaee-platform-dev] The location of
> module-info.java and muti release jar
> Date: Thu, Oct 7, 2021 14:25
> If I understand the plan correctly
> (https://eclipse-ee4j.github.io/jakartaee-platform/jakartaee10/JakartaEE10ReleasePlan
> <https://eclipse-ee4j.github.io/jakartaee-platform/jakartaee10/JakartaEE10ReleasePlan>)
> I thought we are planning to produce API JARs for Jakarta 10
> that are at Java 11 source/target levels.
> With that said, I don't see why we would use multi-release JARs for
> any of the API JARs in Jakarta 10.
> Tom
>
> ----- Original message -----
> From: "Thiago Henrique Hupner" <thihup@xxxxxxxxx>
> Sent by: "jakartaee-platform-dev"
> <jakartaee-platform-dev-bounces@xxxxxxxxxxx>
> To: "jakartaee-platform developer discussions"
> <jakartaee-platform-dev@xxxxxxxxxxx>
> Cc: "jakartaee-platform developer discussions"
> <jakartaee-platform-dev@xxxxxxxxxxx>
> Subject: [EXTERNAL] Re: [jakartaee-platform-dev] The location of
> module-info.java and muti release jar
> Date: Thu, Oct 7, 2021 12:43 PM
> What is possible to do is the following:
> Run the compilation two times: one targeting JDK 11, which will
> compile the module-info, and other targeting JDK 8, will
> override the classes built for JDK 11 with 8, and only the
> module-info will be there.
> I guess using Moditect is also possible.
> On Out 7 2021, at 2:38 pm, Scott Stark <starksm64@xxxxxxxxx> wrote:
>
> How can you produce a jar that can be read by Java SE 8
> unless it is multi-release? The comment there is talking
> about compiling under SE 11 which cannot be read at all by
> SE 8. The most basic class file compiled under 11 blows up
> when using 8:
> *└>
> **/Library/Java/JavaVirtualMachines/jdk1.8.0_261.jdk/Contents/Home/bin/java
> Hello*
> *Error: A JNI error has occurred, please check your
> installation and try again*
> *Exception in thread "main"
> java.lang.UnsupportedClassVersionError: Hello has been
> compiled by a more recent version of the Java Runtime (class
> file version 55.0), this version of the Java Runtime only
> recognizes class file versions up to 52.0*
>
> Sent from Mailspring
> On Oct 7, 2021 at 12:28:19 PM, Emily Jiang via
> jakartaee-platform-dev <jakartaee-platform-dev@xxxxxxxxxxx
> <mailto:jakartaee-platform-dev@xxxxxxxxxxx>> wrote:
>
> Since we are on the topic of module-info, I observed
> different specifications doing different things as far
> as the location goes. Also, some spec produces
> multi-release jar such as Injection spec (see here
> <https://github.com/eclipse-ee4j/injection-api/blob/master/pom.xml#L166>).
> I was told some other specs just place module-info.class
> under root and do not produce a multi release jar as
> module-info.class will be ignored by Java 8 (the api jar
> compiled at Java 8). This is a cleaner way to do it.
> Can we define a convention for this? I know EJB is
> trying to add module-info as well and a long
> conversation is happening(see this
> <https://github.com/eclipse-ee4j/ejb-api/pull/141/files> PR).
> We really need to sort it out on the platform level.
> --
> Thanks
> Emily
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