maven didn't add main-class properly

Question

I want to compile my Java-Project with maven but it didn't add the main-class to the manifest file. So i can't run the jar outside of intellij. I've added the main-class to my pom.xml but it don't show up in the manifest file.

I'm using the build function of intellij on a Win10 machine and maven3 (IntelliJ IDEA 2018.3.1/plugins/maven/lib/maven3).

If i run the jar i get the error

$java -jar myJar.jar
kein Hauptmanifestattribut, in myJar.jar

(German for: no main manifest attribute, in myJar.jar, i don't know the exact english translation for that but it means: no main class specified)

I've tried serveral maven plugins (maven-compile, maven-jar, maven-shade) and ways to specify the main-class but non of them added it to the manifest file. The only way i get this to work is when i added the line

Main-Class: Main

by hand.

my pom file (yes, my main-class called Main and yes it works fine when i added it by hand)

...

    <groupId>com.myname</groupId>
    <artifactId>myProject</artifactId>
    <version>1.0-SNAPSHOT</version>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-jar-plugin</artifactId>
                <configuration>
                    <archive>
                        <manifest>
                            <addClasspath>true</addClasspath>
                            <mainClass>Main</mainClass>
                        </manifest>
                    </archive>
                </configuration>
            </plugin>
        </plugins>
    </build>

    <properties>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>

...

the manifest file

Manifest-Version: 1.0
Archiver-Version: Plexus Archiver
Built-By: dspicuzz
Created-By: Apache Maven 3.3.9
Build-Jdk: 1.8.0_65

If i added the line by hand it runs fine

Manifest-Version: 1.0
Archiver-Version: Plexus Archiver
Built-By: dspicuzz
Created-By: Apache Maven 3.3.9
Build-Jdk: 1.8.0_65
Main-Class: Main

But i can't get maven to generate it for me this way.

Answer 1

I'm using the build function of intellij on a Win10 machine and maven3 (IntelliJ IDEA 2018.3.1/plugins/maven/lib/maven3).

IntelliJ's build will not regenerate your jar file. Try running the package goal to recreate the jar file.

Verify that your package name matches you directory structure: com.mytest.Main

If there is no package it will also work but make sure the directory structure has no package structure either.

This will work:

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>com.myname</groupId>
    <artifactId>runnable</artifactId>
    <version>1.0-SNAPSHOT</version>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-jar-plugin</artifactId>
                <configuration>
                    <archive>
                        <manifest>
                            <addClasspath>true</addClasspath>
                            <mainClass>com.myname.Hello</mainClass>
                        </manifest>
                    </archive>
                </configuration>
            </plugin>
        </plugins>
    </build>

    <properties>
        <maven.compiler.source>1.8</maven.compiler.source>
        <maven.compiler.target>1.8</maven.compiler.target>
    </properties>

</project>

Hello.java

package com.myname;

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

run:

C:\runnable>java -jar target\runnable-1.0-SNAPSHOT.jar
Hello

And, this is the generated manifest file by the maven-jar plugin:

Manifest-Version: 1.0
Archiver-Version: Plexus Archiver
Built-By: egallardo
Created-By: Apache Maven 3.3.9
Build-Jdk: 1.8.0_181
Main-Class: com.myname.Hello

Also check that your sources directory is properly marked in intellij (in light blue) This image is for the packageless version.

These are step by step instructions on how to create the project from scratch using IntelliJ:

• Create New Project
• Choose Maven
• Select your SDK (Java 1.8 or so)
• Leave 'Create from archetype' unchecked
• Click Next
• Group id: com.myapp
• Artifact id: runnable
• Version: 1.0-SNAPSHOT (default)
• Click next
• Project name: runnable (default)
• Project Location: C:\code\java\runnable
• Click Finish
• Select 'Enable auto-import' if prompted
• Copy and past the <build> and <properties> sections to your pom.xml file
• Expand runnable -> src -> main -> java
• right click on java folder and click New -> java class
• Type Main as the new class name and kind: class (default)
• Type psvm and click tab to generate the main method
• Add a print statement: System.out.println("Hello");
• Using the maven tab double click package
• The jar file will be created in C:\code\java\runnable\target\runnable-1.0-SNAPSHOT.jar
• try running it with:

java -jar C:\code\java\runnable\target\runnable-1.0-SNAPSHOT.jar

Check that the jar file date matches the time when you clicked package. If the above doesn't work, you might have found a bug. Try a different JDK version.