[FIXED] Maven Multi-Module-Project works in IntelliJ but running via command line says "java.lang.NoClassDefFoundError"

Issue

I started writing a basic Hello World Multi-Module project with Maven inside IntelliJ. It runs perfectly with the built-in run button, but when I build the project via command line with mvn install and then try running it with java -cp HelloWorld/target/HelloWorld-1.0-SNAPSHOT.jar App, it says

Exception in thread "main" java.lang.NoClassDefFoundError: MoreDataClass at App.main(App.java:5) Caused by: java.lang.ClassNotFoundException: MoreDataClass at java.net.URLClassLoader.findClass(URLClassLoader.java:381) at java.lang.ClassLoader.loadClass(ClassLoader.java:424) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:335) at java.lang.ClassLoader.loadClass(ClassLoader.java:357)

Maybe the problem is the project structure (which was given to my by IntelliJ):

parent/
– pom.xml
– HelloWorld/
– – pom.xml
– – src/main/java/App.java
– GetMoreData/
– – pom.xml
– – src/main/java/MoreDataClass.java

The App.java inside the HelloWorld-Module looks like this:

public class App {
    public static void main(String[] args) {
        System.out.println("Hello World");

        MoreDataClass c = new MoreDataClass();
        System.out.println(c.getMoreData());
    }
}

And the MoreDataClass inside GetMoreData-Module contains this code:

public class MoreDataClass {
    public String getMoreData() {
        return "Here is some more data from the Module GetMoreData";
    }
}

Running App.main() in IntelliJ returns (as supposed to) the following lines at standard out:

Hello World
Here is some more data from the Module GetMoreData

Running it via Maven in the command line (as described at the beginning) on the other hand returns this:

Hello World
Exception in thread "main" java.lang.NoClassDefFoundError: MoreDataClass
    at App.main(App.java:5)
Caused by: java.lang.ClassNotFoundException: MoreDataClass
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:335)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    ... 1 more

So the App.main() is built and can be executed, but it doesn't find the MoreDataClass. Why doesn't it?

In case those are relevant to the problem, here are my pom.xml:

****** parent/pom.xml: ******

<?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>de.playground.multiModule</groupId>
    <artifactId>parent</artifactId>
    <packaging>pom</packaging>
    <version>1.0-SNAPSHOT</version>
    <modules>
        <module>GetMoreData</module>
        <module>HelloWord</module>
    </modules>

</project>

***** parent/GetMoreData/pom.xml *****

<?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">
    <parent>
        <artifactId>parent</artifactId>
        <groupId>de.playground.multiModule</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>GetMoreData</artifactId>

</project>

***** parent/HelloWorld/pom.xml *****

<?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">
    <parent>
        <artifactId>parent</artifactId>
        <groupId>de.playground.multiModule</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>HelloWord</artifactId>

    <dependencies>
        <dependency>
            <groupId>de.playground.multiModule</groupId>
            <artifactId>GetMoreData</artifactId>
            <version>1.0-SNAPSHOT</version>
            <scope>compile</scope>
        </dependency>
    </dependencies>

</project>

Solution

You need to add GetMoreData jar to classpath, or configure the HelloWorlds build to generate jar-with-dependencies

Answered By - user10639668
Answer Checked By - Pedro (JavaFixing Volunteer)