How to account for dependencies in the Assembly jar file?

There are some project on Java with that build.gradle:

plugins {
 id 'java'
 id 'application'
 id 'com.github.johnrengelman.shadow' version '2.0.1'
}
mainClassName = "Main"
group 'org.q'
version '1.0-SNAPSHOT'

sourceCompatibility = 1.8

repositories {
mavenCentral()
jcenter()
}

dependencies {
 testCompile group: 'junit', name: 'junit', version: '4.12'
 compile group: 'net.dv8tion', name: 'JDA', version: '4.1.1_121'
 compile group: 'org.mongodb', name: 'mongodb-driver-sync', version: '3.12.2'
 compile group: 'org.atteo.classindex', name: 'classindex', version: '3.4'
 annotationProcessor group: 'org.atteo.classindex', name: 'classindex', version: '3.4'
}

jar {
 manifest {
 attributes 'Main-Class': 'discordbot.Main'
}
}

compileJava.options.encoding = 'UTF-8'

When you try to build the project into jar by calling the "gradle jar" the file successfully created but when I attempt to execute it(java-jar "path/file.jar") gets the following:

Exception in thread "main" java.lang.NoClassDefFoundError: net/dv8tion/jda/api/JDABuilder
 at discordbot.Main.main(Main.java:17)
Caused by: java.lang.ClassNotFoundException: net.dv8tion.jda.api.JDABuilder
 at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:581)
 at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178)
 at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:521)
 1 ... more

It is logical to assume that the file is going without the dependency, hence the question: how to configure gradle so it was either stick all the dependent libs in the jar, or put them together in the form of jar'nicks and prescribed the classpath?