Modular java module not found - gradle

Question

I read all of the modular documentation but still cannot figure out what the problem is here: I added a dependency via Maven (I also tried adding the jar into project library manually but still caused the same problem), but when I import the class from that particular into my class, IntelliJ says "package com.fazecast.jSerialComm is declared in module 'com.fazecast.jSerialComm' but module com.greeting does not read it".
It gives me two options: Either add it as Maven dependency which I already did (it is in my pom.xml and can see it under dependencies) or "add requires com.fazecast.jSerialComm directive to module-info.java". If I add requires com.fazecast.jSerialComm, it compiles fine, but when I create my modular jar and try to run the jar with java -p mods/ -m com.greeting/com.mayapp.Runner, it tells me "java.lang.module.FindException: Module com.fazecast.jSerialComm not found, required by com.greeting".
I also tried more jars/dependencies which I have and it gave me the same problem. I tried Java 9 and 10, also with Gradle, and created artifact via IntelliJ. Got the same exception. My module-info.java is in src/main/java as where my app starts. Any help will be highly appreciated.
Apache Maven 3.5.4 (1edded0938998edf8bf061f1ceb3cfdeccf443fe; 2018-06-17T14:33:14-04:00)
Maven home: C:\Apache\apache-maven-3.5.4-bin\apache-maven-3.5.4\bin\..
Java version: 9.0.4, vendor: Oracle Corporation, runtime: C:\Program iles\Java\jdk-9.0.4 Default locale: en_US, platform encoding: Cp1252
OS name: "windows 10", version: "10.0", arch: "amd64", family: "windows"
Intelli J 2018.1.6
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.myapp</groupId>
<artifactId>greet</artifactId>
<version>1.0-SNAPSHOT</version>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.7.0</version>
<configuration>
<source>10</source>
<target>10</target>
<release>9</release>
<executable>javac10</executable>
<compilerArgs>
<arg>-Xlint:all,-processing</arg>
</compilerArgs>
<showWarnings>true</showWarnings>
<showDeprecation>true</showDeprecation>
</configuration>
</plugin>
</plugins>
</build>
<dependencies>
<dependency>
<groupId>com.fazecast</groupId>
<artifactId>jSerialComm</artifactId>
<version>2.0.2</version>
<scope>compile</scope>
</dependency>
</dependencies>
</project>
package com.myapp;
import com.fazecast.jSerialComm.SerialPort;
public class Runner {
public static void main(String[] args) {
System.out.println("Runner");
}
}
module com.greeting {
requires com.fazecast.jSerialComm;
}

Answer 1

If you develop a module (as indicated by your module-info.java), all dependencies need to be required (that's the quick fix IntelliJ recommended) and need to be on the module path (instead of the class path) for compilation and launch. For compilation, Maven, Gradle, and IntelliJ do the right thing and when launching your app from IntelliJ, it will do that as well.
The problem most likely lies with your java command:
java -p mods/ -m com.greeting/com.mayapp.Runner
It points to mods as the module path, but unless you forgot to mention some steps you undertook, that folder does not contain your app's dependencies, so when Java goes looking for them, it will not find them - thus the error message.
To get your dependencies into that folder you can either copy them manually (don't forget transitive dependencies) or use Maven's copy-dependencies mojo for that:
<project>
[...]
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-dependency-plugin</artifactId>
<version>3.1.1</version>
<executions>
<execution>
<id>copy-dependencies</id>
<phase>package</phase>
<goals>
<goal>copy-dependencies</goal>
</goals>
<configuration>
<outputDirectory>${project.build.directory}/../mods</outputDirectory>
<overWriteReleases>false</overWriteReleases>
<overWriteSnapshots>false</overWriteSnapshots>
<overWriteIfNewer>true</overWriteIfNewer>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
[...]
</project>
When you run mvn package or mvn install, you will find all dependencies, including transitive ones, in mods and then your command should work.