Loading Maven libraries into GUI project

What is the correct way to load and use a library with Maven? I am trying to use the Gson library for my GUI project, but doing so I get errors. These are my steps:

Creating the Maven project works fine using:

mvn archetype:generate \
    -DgroupId=com.example \
    -DartifactId=my-api-app \
    -DarchetypeGroupId=org.apache.maven.archetypes \
    -DarchetypeArtifactId=maven-archetype-quickstart \
    -DinteractiveMode=false

As I use the OpenJDK version Corretto-22.0.1.8.1 I update the pom.xml (source and target) from 1.7 to 17. The maven-jar-plugin also needs to add the main class to the Manifest.txt, therefore I updated it to:

    <plugin>
      <artifactId>maven-jar-plugin</artifactId>
      <version>3.4.1</version>
      <configuration>
        <archive>
          <manifest>
            <mainClass>com.example.App</mainClass>
          </manifest>
        </archive>
      </configuration>
    </plugin>

The problem starts here. When I add the Gson dependency, I am not able to use it. Doing so leads to an error. The added dependency looks like this:

<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.11.0</version>
</dependency>

Just adding this to the main class:

import com.google.gson.Gson;
...
Gson gson = new Gson();

leads to this error:

Exception in thread "main" java.lang.NoClassDefFoundError: com/google/gson/Gson
        at com.example.App.main(App.java:15)
Caused by: java.lang.ClassNotFoundException: com.google.gson.Gson
        at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:641)
        at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
        at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:525)
        ... 1 more

What am I doing wrong? Why does using the Gson class lead to this error?

Edit 1:

For execution I use the the java command:

java -jar target/my-api-app-1.0-SNAPSHOT.jar

If you want to run your jar as one executable jar, you can use the Shade plugin to encapsulate the dependencies inside. This is consistent with the information you did give about what you did and will allow you to do java -jar target/my-api-app-1.0-SNAPSHOT.jar

<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.example</groupId>
<artifactId>my-api-app</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>jar</packaging>

<name>my-api-app</name>
<url>http://maven.apache.org</url>

<properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.release>17</maven.compiler.release>
    <main.class>com.example.App</main.class>
</properties>

<dependencies>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>3.8.1</version>
        <scope>test</scope>
    </dependency>

    <dependency>
        <groupId>com.google.code.gson</groupId>
        <artifactId>gson</artifactId>
        <version>2.11.0</version>
    </dependency>

</dependencies>
<build>
    <plugins>
        <plugin>
            <artifactId>maven-jar-plugin</artifactId>
            <version>3.4.1</version>
            <configuration>
                <archive>
                    <manifest>
                        <mainClass>${main.class}</mainClass>
                    </manifest>
                </archive>
            </configuration>
        </plugin>

        <plugin>
            <artifactId>maven-shade-plugin</artifactId>
            <version>3.6.0</version>
            <executions>
                <execution>
                    <phase>package</phase>
                    <goals>
                        <goal>shade</goal>
                    </goals>
                    <configuration>
                        <filters>
                            <filter>
                                <artifact>*:*</artifact>
                                <excludes>
                                    <exclude>META-INF/*.SF</exclude>
                                    <exclude>META-INF/*.DSA</exclude>
                                    <exclude>META-INF/*.RSA</exclude>
                                </excludes>
                            </filter>
                        </filters>
                        <transformers>
                            <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                <manifestEntries>
                                    <Main-Class>${main.class}</Main-Class>
                                    <Build-Number>1</Build-Number>
                                </manifestEntries>
                            </transformer>
                        </transformers>
                    </configuration>
                </execution>
            </executions>
        </plugin>

    </plugins>
</build>
</project>