How can I make spark jar file?

ant -f E:\spark2.5.1\build\build.xml

I used the command and got startup.jar .When I run this jar file. It displayed could not find main class?

What’'s wrong?

and I want to know how to use installer4j to build an .exe file?

ant -f E:\spark2.5.1\build\build.xml installer.win

It displayed " Path to Install4j not set, see build.properties.template file"

why ?Anybody can help me?