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Maven - error cannot find or load main class

I tried to build this example : https://github.com/oltzen/JavaCppExample with Maven (mvn clean install) on Linux.
After the successful build, when I run : java de.oltzen.javacppexample.Abc : it says 'could not load or find the main class'
The video tutorial (https://www.youtube.com/watch?v=LZrrqZLhtmw) uses Eclipse and it runs the program with Run as .. Java Application
Is the POM file missing something ?
I tried to add this plugin in POM but it did not work:
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<configuration>
<archive>
<manifest>
<addClasspath>true</addClasspath>
<classpathPrefix>lib/</classpathPrefix>
<mainClass>de.oltzen.javacppexample.Abc</mainClass>
</manifest>
</archive>
</configuration>
</plugin>
I am executing from JavaCppExample/target/classes/ :-
The /classes folder contains package folders : de/oltzen/javacppexample/
The last folder contains the class file Abc.class
So I run the command :
java de.oltzen.javacppexample.Abc
The /target folder contains :
1) classes [folder containing the package]
2) JavaCppExample.jar
3) maven-archiver
4) maven-status
Please help

I added the following plugins for maven copy dependencies and executed java -jar javaCppExample.jar [from /target folder]and it worked. Thanks everyone !
[Simply build using mvn clean install]
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<encoding>UTF-8</encoding>
<target>1.8</target>
<source>1.8</source>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-dependency-plugin</artifactId>
<executions>
<execution>
<id>copy-dependencies</id>
<phase>prepare-package</phase>
<goals>
<goal>copy-dependencies</goal>
</goals>
<configuration>
<outputDirectory>${project.build.directory}/lib/</outputDirectory>
<overWriteReleases>false</overWriteReleases>
<overWriteSnapshots>false</overWriteSnapshots>
<overWriteIfNewer>true</overWriteIfNewer>
</configuration>
</execution>
</executions>
</plugin>
<plugin>
<!-- Build an executable JAR -->
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<version>3.0.2</version>
<configuration>
<archive>
<manifest>
<addClasspath>true</addClasspath>
<classpathPrefix>lib/</classpathPrefix>
<mainClass>de.oltzen.javacppexample.Abc</mainClass>
</manifest>
</archive>
</configuration>
</plugin>

If you are only looking to run your prgramm via maven then use exec-maven-plugin.
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>exec-maven-plugin</artifactId>
<version>1.6.0</version>
<executions>
<execution>
<goals>
<goal>java</goal>
</goals>
</execution>
</executions>
<configuration>
<mainClass>de.oltzen.javacppexample.Abc</mainClass>
</configuration>
</plugin>
Explore more here => https://www.mojohaus.org/exec-maven-plugin/index.html
If you want to build & run as jar then use assembly plugin
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-assembly-plugin</artifactId>
<version>3.1.0</version>
<configuration>
<appendAssemblyId>true</appendAssemblyId>
<descriptors>
<descriptor>${project.basedir}/assembly/assembly.xml</descriptor>
</descriptors>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
<archive>
<manifest>
<mainClass>de.oltzen.javacppexample.Abc</mainClass>
</manifest>
</archive>
</configuration>
<executions>
<execution>
<id>make-assembly</id>
<phase>install</phase>
<goals>
<goal>single</goal>
</goals>
</execution>
</executions>
</plugin>
Explore more about Maven assembly plugin to customize to your needs.

Bind jar:test-jar to package phase

I have a pom snippet containing the following:
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<version>2.6</version>
<configuration>
<archive>
<manifest>
<addClasspath>true</addClasspath>
<classpathPrefix>lib/</classpathPrefix>
<mainClass>com.jason.Main</mainClass>
</manifest>
<manifestEntries>
<Class-Path>resources/</Class-Path>
</manifestEntries>
</archive>
<executions>
<execution>
<id>package-test-jar</id>
<phase>package</phase>
<goals>
<goal>test-jar</goal>
</goals>
</execution>
</executions>
</configuration>
</plugin>
When i run "mvn package", the plugin does not execute and my test jar does not get created. When i run "mvn jar:test-jar" my jar gets created. Does anyone know why that might be?
Thank you kindly,
Jason

You misplaced the <executions> block: it should be outside of the <configuration> one.
As you wrote it, it means that you pass a structure of parameters named "executions" to the configuration of the maven jar plugin, which is simply ignored.
Here's the correct configuration:
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<version>2.6</version>
<configuration>
... your configuration data ...
</configuration>
<executions>
<execution>
<id>package-test-jar</id>
<phase>package</phase>
<goals>
<goal>test-jar</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
Note that specifying the "package" phase for your execution isn't necessary, since the maven jar plugin is attached by default to this phase.

maven copy dependecies not working

This question ha sbeen asked but none of the solutions worked for me so:
I want to copy my jars which are specified through the dependency tags in the build of POM.xml:
<dependency>
...
</dependency>
into a folder like target/lib
pom.xml:
<build>
<defaultGoal>install</defaultGoal>
<directory>${basedir}/target</directory>
<finalName>${project.artifactId}-${project.version}</finalName>
<pluginManagement>
<plugins>
<plugin>
<groupId>com.googlecode.addjars-maven-plugin</groupId>
<artifactId>addjars-maven-plugin</artifactId>
<version>1.0.5</version>
<executions>
<execution>
<goals>
<goal>add-jars</goal>
</goals>
<configuration>
<resources>
<resource>
<directory>${project.build.directory}/my-repo</directory>
</resource>
</resources>
</configuration>
</execution>
</executions>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<configuration>
<archive>
<manifest>
<classpathPrefix>lib/</classpathPrefix>
<addClasspath>true</addClasspath>
<mainClass>Swapper</mainClass>
</manifest>
</archive>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-dependency-plugin</artifactId>
<version>2.10</version>
<executions>
<execution>
<id>copy-dependencies</id>
<phase>package</phase>
<goals>
<goal>copy-dependencies</goal>
</goals>
<configuration>
<includeScope>runtime</includeScope>
<outputDirectory>${project.build.directory}/lib/</outputDirectory>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</pluginManagement>
</build>
Like i said, nothing is copied at all. But according to some Q&A on this portal it should work.
Any ideas?

You are declaring your plugins in your <pluginManagement> section. This is all well and good, but if want them to execute you need to declare them outside the <pluginManagement> section:
<build>
<pluginManagement>
...
</pluginManagement>
<plugins>
<plugin>
<artifactId>addjars-maven-plugin</artifactId>
</plugin>
<plugin>
<artifactId>maven-jar-plugin</artifactId>
</plugin>
<plugin>
<artifactId>maven-dependency-plugin</artifactId>
</plugin>
</plugins>
</build>
Think of <pluginManagement> in the same way you think of <dependencyManagement>, but for plugins.

Add in goal like below based on your plugin
mvn clean install dependency:copy-dependencies

Try to replace :
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<configuration>
<archive>
<manifest>
<classpathPrefix>lib/</classpathPrefix>
<addClasspath>true</addClasspath>
<mainClass>Swapper</mainClass>
</manifest>
</archive>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-dependency-plugin</artifactId>
<version>2.10</version>
<executions>
<execution>
<id>copy-dependencies</id>
<phase>package</phase>
<goals>
<goal>copy-dependencies</goal>
</goals>
<configuration>
<includeScope>runtime</includeScope>
<outputDirectory>${project.build.directory}/lib/</outputDirectory>
</configuration>
</execution>
</executions>
</plugin>
By This :
<build>
<plugins>
<plugin>
<artifactId>maven-assembly-plugin</artifactId>
<configuration>
<outputDirectory>${project.build.directory}/lib/</outputDirectory>
<archive>
<manifest>
<mainClass>Swapper</mainClass>
</manifest>
</archive>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
</configuration>
<executions>
<execution>
<id>make-assembly</id>
<phase>package</phase>
<goals>
<goal>single</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>

Deploy Spark-Microframework to Server

I have developed a simple Spark-Web app that runs fine when started through my IDE (IntelliJ). However, when I run the generated .jar (or .war - i have tried creating both) I get a manifest error:
no main manifest attribute, in build/libs/ProjectName-0.1.war
My goal is to run it stand-alone on a test server. I have read through How to deploy a spark Java web app? but it's not specific on how to start the app - I am guessing it's by running:
java -jar ProjectName-0.1.war
which results in the error that brought me here.
EDIT: Using Gradle 2.2.1

I have a sample app which you can deploy (https://github.com/mnrasul/sparkjava-testapp).
In my pom, I have the relevant sections for building a fat jar. At the end, there is a way to generate a debian file too. Not sure if I finished that part, but you can certainly work with the fat jar.
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-assembly-plugin</artifactId>
<version>2.4.1</version>
<configuration>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
<archive>
<manifest>
<addClasspath>true</addClasspath>
<mainClass>ca.rasul.sparkjava.testapp.HelloWorld</mainClass>
</manifest>
</archive>
</configuration>
<executions>
<execution>
<id>assemble-all</id>
<phase>package</phase>
<goals>
<goal>single</goal>
</goals>
</execution>
</executions>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<configuration>
<archive>
<manifest>
<addClasspath>true</addClasspath>
<mainClass>ca.rasul.sparkjava.testapp.HelloWorld</mainClass>
</manifest>
</archive>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.1</version>
<configuration>
<source>${java.version}</source>
<target>${java.version}</target>
</configuration>
</plugin>
<!--building a deb package-->
<plugin>
<artifactId>jdeb</artifactId>
<groupId>org.vafer</groupId>
<version>1.3</version>
<executions>
<execution>
<phase>package</phase>
<goals>
<goal>jdeb</goal>
</goals>
<configuration>
<dataSet>
<data>
<src>${project.build.directory}/${project.build.finalName}.jar</src>
<type>file</type>
<mapper>
<type>perm</type>
<prefix>/usr/share/jdeb/lib</prefix>
</mapper>
</data>
</dataSet>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>

Integrating slf4j with maven

Hello guys I am new to Maven and I am trying to integrate slf4j in a maven project
Here is my pom.xml file
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.7.9</version>
</dependency>
And I have these two lines in my main function
Logger logger = LoggerFactory.getLogger(App.class);
logger.info("Hello World");
Project is compiled and packaged successfully but when I try to run it
through
java -cp target/maven-1.0-SNAPSHOT.jar com.goutam.maven.App
The following Exception is thrown
Exception in thread "main" java.lang.NoClassDefFoundError: org/slf4j/LoggerFactory
at com.goutam.maven.App.main(App.java:11)
Caused by: java.lang.ClassNotFoundException: org.slf4j.LoggerFactory
at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
at java.lang.ClassLoader.loadClass(ClassLoader.java:358)

build fat jar with maven
add this to your pom.xml
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-assembly-plugin</artifactId>
<version>2.5.3</version>
<configuration>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
</configuration>
<executions>
<execution>
<id>assemble-all</id>
<phase>package</phase>
<goals>
<goal>single</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
and then run
java -cp target/maven-jar-with-dependencies-1.0-SNAPSHOT.jar com.goutam.maven.App
note: pick the jar file which has jar-with-dependencies

Maven will not by itself bundle all dependencies for you, so your resulting "maven-1.0-SNAPSHOT.jar" does not contains sl4j (nor any of its own dependencies).
If you want your command line to work, you need to include all the librairies inside your jar. This can be achieved using the Maven Assembly Plugin with something like:
<plugin>
<artifactId>maven-assembly-plugin</artifactId>
<version>2.5.3</version>
<configuration>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
<archive>
<manifest>
<mainClass>org.sample.App</mainClass>
</manifest>
</archive>
</configuration>
<executions>
<execution>
<id>make-assembly</id>
<phase>package</phase>
<goals>
<goal>single</goal>
</goals>
</execution>
</executions>
</plugin>

I don't like the idea of building fat jars, as we loose some flexibilities in this approach.
Rather would advocate for copy-dependencies plugin in maven.
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-dependency-plugin</artifactId>
<version>2.9</version>
<executions>
<execution>
<id>copy-dependencies</id>
<phase>install</phase>
<goals>
<goal>copy-dependencies</goal>
</goals>
<configuration>
<outputDirectory>${project.build.directory}/lib</outputDirectory>
<overWriteReleases>false</overWriteReleases>
<overWriteSnapshots>false</overWriteSnapshots>
<overWriteIfNewer>true</overWriteIfNewer>
</configuration>
</execution>
</executions>
</plugin>
Coupling it along with maven-jar-plugin. Read this for details.
Assuming the third party dependencies are copied into target/lib folder.
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<version>2.5</version>
<configuration>
<archive>
<manifest>
<mainClass>main class</mainClass>
<addClasspath>true</addClasspath>
<classpathPrefix>lib/</classpathPrefix>
</manifest>
</archive>
</configuration>
</plugin>

Two other answers recommend maven-assembly-plugin. I think you're generally better served with the maven-shade-plugin.
<project>
...
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-shade-plugin</artifactId>
<version>2.3</version>
<configuration>
<!-- put your configurations here -->
</configuration>
<executions>
<execution>
<phase>package</phase>
<goals>
<goal>shade</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
...
</project>