Java 11 Eclipse finds automatic module, Maven does

Question

I'm attempting to upgrade a 15 year old Maven multimodule project to Java 11, and the module system that was introduced in Java 9. Since the project is built using Maven, all dependencies are pretty clear. First I want to do this using the automatic module names, in order not to also introduce upgraded artifacts (if not absolutely required).

Eclipse is pretty helpful in this process, autocompleting the automatic module names in the module-info.java. For example:

requires dom4j;

But if I compile with Maven, I get errors about that it cannot find the modules Eclipse just autocompleted in there.

module-info.java:[29,18] module not found: dom4j

I am using Maven's compiler plugin 3.7.0 (3.8.0 gives a NullPointerException as per https://jira.apache.org/jira/browse/MCOMPILER-355) I suspect Maven is setting the jars up on the classpath instead of on the modulepath, but the compiler's plugin debug output does not log that.

How can I make Maven correctly handle those modules?

Answer 1

I was running into the same issue. Adding

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.8.1</version>
        </plugin>
    </plugins>
</build>

to my pom solved the problem for me...