Upgrading EE modules (was Re: modulepath and classpath mixture)

[Alan Bateman]

On 22/03/2016 22:29, Richard Opalka wrote:
> Hi,
>
>    I'm experiencing the same problem locally.
> When trying to build Oracle provided maven artifact from sources, namely
>
> http://search.maven.org/#artifactdetails|javax.annotation|javax.annotation-api|1.2|jar 
>
>
> the build fails on JDK9 (with Jigsaw) with message:
>
> ./src/javax/annotation/Priority.java:42: error: package exists in 
> another module: java.annotations.common
> package javax.annotation;
> ^
> 1 error
>
> How is Jigsaw javac going to deal with such compilation scenarios?
I've changed the subject line as this issue seems to be about how to 
compile with, and make use of, the EE versions of the so-called "Common 
Annotations".

The JSR 250 defined Common Annotations is one of a small number of APIs 
that is shared between Java SE and Java EE. Java SE defines a subset, 
where Java EE defines the full API (or the full set of annotations in 
this case). With JDK 8 and older then Java EE or app servers needed to 
deploy an EE version to override the Java SE version. The only supported 
way of doing this was via the endorsed standards override mechanism 
(that mechanism was documented for both endorsed standards and 
standalone technologies with JSR 250 one of the standalone technologies).

As things currently stand, the replacement to the endorsed standards 
override mechanism is upgradeable modules. In JEP 261 you will see the 
option -upgrademodulepath that can be used to deploy modules that 
upgrade/override modules in the JDK.

So what you need here is the Java EE version of the 
java.annotations.common module and deploy it via -upgrademodulepath to 
upgrade/override the module in the JDK.

Unfortunately there isn't an EE version of this module yet so you have 
to create it yourself. Not hard, you just need to compile the following 
module-info.java and put it in the top-level directory of the JAR file 
to make it a modular JAR.

module java.annotations.common {
     exports javax.annotation;
     exports javax.annotation.security;
     exports javax.annotation.sql;
}

Note that the Java SE/JDK version exports one package, the Java EE 
version exports three packages.

You can check that the EE version is observable with the following common:

   java -upgrademodulepath libs/javax.annotation-api.jar -listmods

or -listmods:java.annotations.common to have the module definition 
printed so that you can checks the exports.

-Alan