First, it's kind of weird, to see you run java -jar "app" and not java -jar app.jar

Second, to make a jar executable... you need to jar a file called META-INF/MANIFEST.MF

the file itself should have (at least) this one liner:

Main-Class: com.mypackage.MyClass

Where com.mypackage.MyClass is the class holding the public static void main(String[] args) entry point.

Note that there are several ways to get this done either with the CLI, Maven, Ant or Gradle:

For CLI , the following command will do: (tks @dvvrt)

jar cmvf META-INF/MANIFEST.MF <new-jar-filename>.jar  <files to include>

For Maven , something like the following snippet should do the trick. Note that this is only the plugin definition, not the full pom.xml :

      <!-- Build an executable JAR -->

(Pick a <version> appropriate to your project.)

For Ant , the snippet below should help:

<jar destfile="build/main/checksites.jar">
  <fileset dir="build/main/classes"/>
  <zipfileset includes="**/*.class" src="lib/main/some.jar"/>
    <attribute name="Main-Class" value="com.acme.checksites.Main"/>

Credits Michael Niemand -

For Gradle :

plugins {
    id 'java'

jar {
    manifest {
                'Main-Class': 'com.mypackage.MyClass'