GsonBuilder cannot be found in JavaFX + Maven project's runnable jar - eclipse

Question

Background
I'm developing a Maven project + JavaFX in Eclipse.
My application uses Gson for serialization.
Of course, when you haven't included Gson.jar then Eclipse will complaint that GsonBuilder (or any part of gson library for that matter) cannot be found.
I included the library through Maven dependency
After this, Eclipse is cool and I can import GsonBuilder (or any part of gson library for that matter).
Everything is good.
And mvn clean install works with no error.
The Problem:
I go to target directory and execute java -jar myapplication.jar
Exception in thread "JavaFX Application Thread" java.lang.NoClassDefFoundError: com/google/gson/GsonBuilder
at app.MyApplication.<clinit>(MyApplication.java:68)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:348)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplicationWithArgs$153(LauncherImpl.java:352)
at com.sun.javafx.application.LauncherImpl$$Lambda$46/683287027.run(Unknown Source)
at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$172(PlatformImpl.java:326)
at com.sun.javafx.application.PlatformImpl$$Lambda$47/254413710.run(Unknown Source)
at com.sun.javafx.application.PlatformImpl.lambda$null$170(PlatformImpl.java:295)
at com.sun.javafx.application.PlatformImpl$$Lambda$49/1171144110.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$171(PlatformImpl.java:294)
at com.sun.javafx.application.PlatformImpl$$Lambda$48/553264065.run(Unknown Source)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
Caused by: java.lang.ClassNotFoundException: com.google.gson.GsonBuilder
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 13 more
Exception in thread "main" java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:767)
Caused by: java.lang.NullPointerException
at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:383)
at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:328)
... 5 more
So, can you please help me out here? What's happening and how can I fix this?
Why is it not detected? I mean, the compiler compiles without error. So, gson must be there.
I also tried to exclude and reinclude the library. No result.

Answer 1

#dunni is right.
I used maven-jar-plugin instead maven-assembly-plugin.
After adding my pom.xml with
<build>
<plugins>
<plugin>
<artifactId>maven-assembly-plugin</artifactId>
<configuration>
<archive>
<manifest>
<mainClass>my.main.class</mainClass>
</manifest>
</archive>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
</configuration>
</plugin>
</plugins>
</build>
Then, execute:
mvn clean compile assembly:single
mvn install
there is an executable jar with postfix jar-with-dependencies in target directory.
Afterwards, executing java -jar target/myapp-jar-with-dependencies.jar works like a charm.