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How do I run a .java file from the command line, Maven?

I want to run my main class which is present in the src/comm instead of src/java/main.
I tried using:
mvn exec:java -Dexec.mainClass=src.communication.Launcher.Launcher
This statement gives me the "class not found exception".
The hierarchy is like src/communication is the source folder, then Launcher is package and the Launcher.java is the class file.
How can I execute this file from the command line as my main function is inside this class?

Use maven-jar-plugin and put in the manifest in your main class,
but it is better to use src/java/main than the other folder.
<build>
<plugins>
<plugin>
<!-- Build an executable JAR -->
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<version>3.0.2</version>
<configuration>
<archive>
<manifest>
<mainClass>pacakgeAndClasseName</mainClass>
</manifest>
</archive>
</configuration>
</plugin>
</plugins>
</build>

Hadoop HDFS - executing JAR file on virtual machine

I have built a Java application with Maven in NetBeans. When I built Main project (Run -> build Main project) I got a JAR file called ROVKP_3zad-1.0-SNAPSHOT.jar with only one class called Main.
Then I put that JAR file on Virtual Machine and tried to execute this from command line, from folder where the JAR file is placed:
hadoop jar ROVKP_3zad-1.0-SNAPSHOT.jar com.mycompany.rovkp_3zad.Main
And I got an error saying:
Exception in thread "main" java.lang.ClassNotFoundException: Main
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:348)
at org.apache.hadoop.util.RunJar.run(RunJar.java:214)
at org.apache.hadoop.util.RunJar.main(RunJar.java:136)
What could be the cause? In my .pom file it is, besides other, defined:
<name>ROVKP_3zad</name>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<version>2.6</version>
<configuration>
<archive>
<manifest>
<addClasspath>true</addClasspath>
<mainClass>Main</mainClass>
</manifest>
</archive>
</configuration>
</plugin>
</plugins>
</build>
so I think there is not problem with dependencies and classpath. Thank you very much for your help.

Change your POM to:
<name>ROVKP_3zad</name>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<version>2.6</version>
<configuration>
<archive>
<manifest>
<addClasspath>true</addClasspath>
<mainClass>com.mycompany.rovkp_3zad.Main</mainClass>
</manifest>
</archive>
</configuration>
</plugin>
</plugins>
</build>

ClassNotFoundException when running a jar but not when running the app directly

My app is facing a NoClassDefFoundError when trying to access external dependencies, but only when run as a jar.
Using Intellij, I have a simple app with main class with some calls to external dependencies such as slf4j.
public class Main {
private static final Logger logger = LoggerFactory.getLogger(Main.class);
///
public static void main(String[] args) {
logger.debug("start");
}
}
The pom.xml includes the relevant dependencies and the app is compiled successfully.
When running the app from the intellij as regular application it is running with no problem.
But when creating an executable jar out of it and trying to run it, it crashes and can't find external dependencies:
java.lang.NoClassDefFoundError: org/slf4j/LoggerFactory
at com.example.Main.<clinit>(Main.java:18)
Caused by: java.lang.ClassNotFoundException: org.slf4j.LoggerFactory
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:338)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 1 more
Exception in thread "main"
Process finished with exit code 1
I added this to the pom to try to solve the problem, but it didn't help:
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</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>com.example.Main</mainClass>
</manifest>
</archive>
</configuration>
</plugin>
</plugins>
</build>
The manifest file is located in src/main/resources/META-INF/MANIFEST.MF:
Manifest-Version: 1.0
Main-Class: com.example.Main

It's simple to understand. The jar that you are creating contains only the .class files of your code, not of the other libraries that you're importing. So when you run your code, it is unable to find the external library (org.slf4j in this case) that you have referenced in your code.
I don't know about the maven jar plugin that you're using, but try the maven assembly plugin. This plugin is used to bundle up all the other libraries that you use along with your code and create a "bundled" jar. Add the following to your pom.xml. You can add this portion between <plugins> and </plugins>.
<plugin>
<artifactId>maven-assembly-plugin</artifactId>
<executions>
<execution>
<id>example</id>
<configuration>
<archive>
<manifest>
<mainClass>com.example.Main</mainClass>
</manifest>
</archive>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
<appendAssemblyId>false</appendAssemblyId>
</configuration>
<phase>package</phase>
<goals>
<goal>single</goal>
</goals>
</execution>
</executions>
</plugin>
This additionally binds this "assembly" goal to the package phase of maven. So mvn package should create your jar.

Your meta-inf should have following attributes
Manifest-Version: 1.0
Created-By: xxxx
Main-Class: com.sample.Main
ClassPath: path/to/jars/your.jar
java -cp yourpath/example.jar com.sample.Main
Or
java -jar example.jar

Run Java Maven project with Linux command line

I have a Java project that prints "Hello world !". It runs well under Eclipse/Windows and on a Linux server with the command:
java MyClass.java; javac MyClass
Now that I have converted the project to a Maven project it's still running fine in Eclipse, but I can't find how to run it with a Linux command. I tried many answers that I found on forums but none work for me.
Here is an example of what I tested:
mvn package install;
cd target;
java -cp myApp-0.0.1-SNAPSHOT.jar mypackage.Mylass;
This results to an error:
Error: Could not find or load main class mypackage.Mylass
So, how can I run the Maven code on Linux without generating a jar file or at least make it work with a command line?

i finally managed to make it work thanks to all the answers.
here is what i did
i moved my Main class to the outside of packages and deleted/regenerated a new POM file with
<manifest>
<mainClass>Myclass</mainClass>
</manifest>
but i got some dependency errors so i generated a jar file with the dependency by adding maven plugin jar-with-dependencies
so here is what the build part of my POM file looks like now
....
</dependencyManagement>
<build>
<sourceDirectory>src</sourceDirectory>
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.0</version>
<configuration>
<source>1.7</source>
<target>1.7</target>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<configuration>
<archive>
<manifest>
<mainClass>MyClass</mainClass>
</manifest>
</archive>
</configuration>
</plugin>
<plugin>
<artifactId>maven-assembly-plugin</artifactId>
<version>3.0.0</version>
<configuration>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
<archive>
<manifest>
<mainClass>MyClass</mainClass>
</manifest>
</archive>
</configuration>
<executions>
<execution>
<id>make-assembly</id> <!-- this is used for inheritance merges -->
<phase>package</phase> <!-- bind to the packaging phase -->
<goals>
<goal>single</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
and here is how i execute it .
rm -rf target/ #delete old generated files
mvn install package # generate new jar files
java -jar target/App-0.0.1-SNAPSHOT-jar-with-dependencies.jar # execution
i hope this can save someone else's time
thanks for your help

You've specify a main class in the manifest of myApp-0.0.1-SNAPSHOT.jar
Add the next snippet of code to your pom file.
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<configuration>
<archive>
<manifest>
<mainClass>mypackage.Mylass</mainClass>
</manifest>
</archive>
</configuration>
</plugin>
</plugins>
</build>
This's the complete pom.file
http://maven.apache.org/maven-v4_0_0.xsd">
4.0.0
com.mycompany.app
my-app
jar
1.0-SNAPSHOT
my-app
http://maven.apache.org
junit
junit
3.8.1
test
<dependency>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.6.1</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<configuration>
<archive>
<manifest>
<mainClass>com.mycompany.app.App</mainClass>
</manifest>
</archive>
</configuration>
</plugin>
</plugins>
</build>

Can you confirm the class name you can trying to run ?
As per your comment, originally ran the class using below command.
java MyClass.java; javac MyClass - here the class name is MyClass
After maven install, it should be invoked using
mvn package install;
cd target;
java -cp myApp-0.0.1-SNAPSHOT.jar mypackage.MyClass;

Missing Main-Class attibute in MANIFEST.MF in Maven generated jar file

I am currently experimenting with Maven in Eclipse (m2e-Plugin) and tried to build and run the Hello World example project. However, when launching the generated jar, nothing happens. I checked the MANIFEST.MF and noticed that the Main-Class attribute was missing. After adding the attribute, the jar could be launched.
Why does Maven not add this attribute?

Have a look at this link:
https://maven.apache.org/shared/maven-archiver/examples/classpath.html#aAdd
You can find there how to configure your maven project to run specific class. You have to add maven-jar-plugin configuration with mainClass defined.
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
...
<configuration>
<archive>
<manifest>
<addClasspath>true</addClasspath>
<mainClass>fully.qualified.MainClass</mainClass>
</manifest>
</archive>
</configuration>
...
</plugin>
</plugins>