CODEWITHSUNDEEP
eclipsemoduleprojectjava-9java-platform-module-system
Arceus
Arceus

Reputation: 540

Define a Java 9 multi-moduled project in Eclipse

I'm trying out Java 9 Jigsaw module system (no module experience yet) and would like to use it for capsuling the classes within my project, but it's confusing.

According to this article it should be possible to have multiple modules within ONE project. I made a new project in Eclipse Oxygen (Java 9 is supported) with the same structure as shown in the article. But Eclipse keeps telling me that I must not have more than one module-info.java in a project.

I really don't know how to tell Eclipse that it should use the "multi-module-mode". And I really would appreciate not having to create a new project for every single module.

This works:

enter image description here

This not:

enter image description here

But according to this article something like that should work:

enter image description here

And how about deployment of a modularized project with Eclipse? There is nothing to see about the new jmod extension. Do I still export it as a runnable JAR file like before?

Notice that my questions refer to working with the IDE (no command line, I mean with an IDE that should be possible, right?) Thank you for enlightening me.

Upvotes: 19

Views: 3779

Answers (2)

SergeFan
SergeFan

Reputation: 21

I don't know if this question is still open for an answer, but you can solve this problem by simply removing all source folders on the build path. At least this works for Eclipse 2021-12 version.

As you can see this is a demo project from the Official Gradle Guide Book and it has multiple modules. Each module has its own module-info.java.

project structure in IntelliJ IDEA

If I open this project in Eclipse it will give me the 'duplicated entries on module-info.java' error.

Eclipse shows the error

But if I delete all the source folders on the build path, the error is gone and the project can be built and run without problem.

project properties: Java build path

The only problem is that you have to build the project with Gradle so that it will produce the .jar of each module and you have to include them in the libraries later.

include all the .jar in libraries

I think this is probably the same solution mentioned by howlger above.

Upvotes: 2

howlger
howlger

Reputation: 34165

Currently, Eclipse requires you to create a separate project for each module (e. g. because each module has its own Java Build Path).

To understand this design decision, consider that Java modules correspond to OSGi bundles / Eclipse plug-ins and it has always been to have a separate project for each bundle/plug-in. If you come from the Maven world, you would probably expect a deeper folder structure instead. But modules are self-contained and combining several modules into one project would only add an additional folder level without meaning. However, Eclipse supports nested projects and so-called working sets if you need an additional folder level.

Exporting modules as images is planned for Eclipse 2019-03 (4.11), on March 20, 2019 (see Eclipse bug 518445). Exporting modules as JARs that can be used on the modulepath (-m) already works (see my video).

Upvotes: 14

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