When you develop a stand-alone Java application, Maven can create the executable jar for you, with main-class and classpath manifest entries. You just need the configuration of the maven-jar-plugin shown below.

The sample pom.xml also specifies that we use Java 7 and UTF-8. You can take out the sourceEncoding and maven-compiler-plugin configurations, if you want to go with defaults instead.

<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>net.doepner</groupId>
    <artifactId>executable-jar-sample</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <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>
                <version>2.4</version>
                <configuration>
                    <archive>
                        <manifest>
                            <addClasspath>true</addClasspath>
                            <mainClass>net.doepner.sample.Main</mainClass>
                        </manifest>
                    </archive>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

Here is a matching minimal main class, src/main/java/net/doepner/sample/Main.java:

package net.doepner.sample;

import javax.swing.JOptionPane;

/**
 * The class that has the main method
 */
public class Main {

    public static void main(String[] args) {
        JOptionPane.showMessageDialog(null, "It works!");
    }
}