multi-release jar for jdk11+ missing

[lanthale]

I am using the lib for a javafx application which I have ported from javafx8 to javafx11 and openjdk 11.

In order to use the lib I had to modularize the lib myself and therefore the question if it is possible to get a multi-release jar which can be used in java8 and java 9+ ?

Here is my config to use the lib (I have used moditec to modularize the lib):

<dependency>
            <groupId>com.github.bbottema</groupId>
            <artifactId>emailaddress-rfc2822</artifactId>
            <version>2.1.3</version>
            <exclusions>
                <exclusion>
                    <groupId>*</groupId>
                    <artifactId>*</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>com.sun.activation</groupId>
            <artifactId>jakarta.activation</artifactId>
            <version>1.2.1</version>
        </dependency>
        <dependency>
            <groupId>com.sun.mail</groupId>
            <artifactId>jakarta.mail</artifactId>
            <version>1.6.4</version>
            <exclusions>
                <exclusion>
                    <groupId>*</groupId>
                    <artifactId>*</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.simplejavamail</groupId>
            <artifactId>simple-java-mail</artifactId>
            <version>5.5.1</version>
            <exclusions>
                <exclusion>
                    <groupId>*</groupId>
                    <artifactId>*</artifactId>
                </exclusion>
            </exclusions>
</dependency>

Moditec config file or input for module-info.java

<module>
                                    <artifact>
                                        <groupId>org.simplejavamail</groupId>
                                        <artifactId>simple-java-mail</artifactId>                                   
                                    </artifact>                                    
                                    <moduleInfoSource>
                                        open module simple.java.mail {                                                                                                                                                                                                                                                                                                                                                                
                                        
                                        requires java.desktop;
                                        requires jakarta.mail;
                                        requires jakarta.activation;
                                        requires emailaddress.rfc2822; 
                                        requires org.slf4j;                                       
                                        
                                        exports org.simplejavamail;
                                        exports org.simplejavamail.converter;
                                        exports org.simplejavamail.email;
                                        exports org.simplejavamail.internal.util;
                                        exports org.simplejavamail.mailer;
                                        exports org.simplejavamail.outlookmessageparser.simplejavamail;
                                        exports org.simplejavamail.outlookmessageparser.simplejavamail.model;
                                        exports org.simplejavamail.outlookmessageparser.simplejavamail.rtf;
                                        exports org.simplejavamail.outlookmessageparser.simplejavamail.rtf.util;
                                        exports org.simplejavamail.springsupport;
                                        exports org.simplejavamail.util;
                                        }
                                    </moduleInfoSource>
                                </module> 

[bbottema]

Uhm, modularity is a little beyond my knowledge currently, but I have done some module-related work on the upcoming 6.0.0 release in the develop branch. I'm close to releasing it, would you mind trying a snapshot of that to see if it meets your requirements?

Otherwise, I'm happy to work with you to make it Java9+ compatible.

[lanthale]

I will try that out. It is not so complicated at all you have just create a module-info.java(content is in my first post) in the root of the source folder and compile it with Option -release 8 and afterwards again with -release 11 for java9+. So you have inside the source folder another source folder for java 9+ which includes just the module-info.java. The rest of the code remains as it is.

But if you want to switch to java 9+ for the whole lib than create the module-info.java in the root folder and compile with java 9+ normally and you have the lib ready.

You can have a look here for more details:
https://www.baeldung.com/java-multi-release-jar

https://maven.apache.org/plugins/maven-compiler-plugin/multirelease.html

[bbottema]

Ok, so multireleases is something mostly useful for the library maintainers: they can leverage JDK functions that are not available in earlier JDKs and then release multiple versions of a class file in a single jar.

My question now is, why do you need this?

In order to use the lib I had to modularize the lib myself

I was under the impression that the module system is backwards compatible, split packages notwithstanding.

Why would I need two releases? Personally I'm not interested in maintaining two code bases.

[lanthale]

Yes and no. The format of the module-info.java is only understand by a compiler greater than java 9. If you create the module-info.java and compile it with java 8 you will get errors. This is the only reason for the multirelease jar files. The multi-release jar prevents you from creating two jar files (one for java8 and one for java9) with two code bases.

Which JDK are you using to build the lib ?

For the reason above multi-release jar is the solution.
In this case in the directory for java 9+ only consists of the module-info.java. Therefore the compiler can create class files for java8 without the module-info.class and for the java9+ with the module-info.class. All other classes stay the same.

[lanthale]

In the evening I will try it out and let write you what in the pom.xml must be changed and which file to place in which directory to archive all this above.

[lanthale]

I have tried to commit but I think it was not successfully.

Please can you use the following maven plugin (readme explains that in more details):
https://github.com/metlos/multi-release-jar-maven-plugin

But you have to compile with java 9 at least. If you use java 11 you have to use additionally libs such as java.xml (was removed in java 11).

src/main/java-mr/9/module-info.java with the following content:

open module simple.java.mail {                                                                                                                                                                                                                                                                                                                                                                
                   
    requires java.desktop;
    requires jakarta.mail;
    requires jakarta.activation;
    requires emailaddress.rfc2822; 
    requires org.slf4j;                                       
                                        
    exports org.simplejavamail;
    exports org.simplejavamail.converter;
    exports org.simplejavamail.email;
    exports org.simplejavamail.internal.util;
    exports org.simplejavamail.mailer;
    exports org.simplejavamail.outlookmessageparser.simplejavamail;
    exports org.simplejavamail.outlookmessageparser.simplejavamail.model;
    exports org.simplejavamail.outlookmessageparser.simplejavamail.rtf;
    exports org.simplejavamail.outlookmessageparser.simplejavamail.rtf.util;
    exports org.simplejavamail.springsupport;
    exports org.simplejavamail.util;
}

[bbottema]

I'm still not clear on the issue here. What problem are we solving?

Why are you unable to use the library as-is? Newer JDK's should be backwards compatible with legacy jars, with the exception of split packages and J2EE modules.

[lanthale]

I have now commit a working version which is usable with java9+ and has a minimal module-info.java included. For that I had to add some dependend jars and change the packaging goal from jar to multi-release-jar. At last I had to add two properties <maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>

I tried to commit but had no right to commit and therefor as attachment the files.
pom.xml.zip
module-info.java.zip

Have a look on it and see if that is ok for you.

[bbottema]

@lanthale, you are focusing on the solution, while I'm still trying to understand the problem (or rather I fail to see a problem to begin with). So if you could please help me understand the problem if there really is one, then maybe we can move on to a solution.

[lanthale]

Sorry I was too fast.
The problem is that actually your lib is treated as an automatic module in java 9 or newer which means that it is not possible to use jlink to create a distributable java app on any platform.

For a java-ee app on an application server this is not a problem, but for a desktop app it is.

So the files I added before are just adding the necessary information so that the lib is a valid named module with a defined interface for java beyond 9 and that the lib is in parallel useable under java 7 / 8.

Hopefully that clarified the issue a bit.
Do you have any questions ?